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2017 Summer Disease Management Review

By: Bryan Hed

As we move into the post-bloom period, we are reminded that the immediate pre-bloom spray and the first post bloom spray are the most important you’ll make all season. These two sprays protect the nascent crop during its most vulnerable period and are essential to a fruit disease management program for control of the four major grape diseases; powdery and downy mildew, black rot, and Phomopsis. Use ‘best’ materials, shortest intervals, best coverage, etc., for those two sprays, EVERY YEAR! No matter what varieties you grow, those two sprays are the most important for protection of your crop. For growers of Vitis vinifera and many of the French hybrids, the second and perhaps third post-bloom sprays are also of critical importance, especially in a wet year and in vineyards that have already developed some observable level of disease this season. That said, let’s review these major diseases.

First, there’s Black rot caused by the fungus Guignardia bidwellii. This fungus can infect all immature green parts of the vine: fruit, shoots, leaves, and tendrils. On leaves, infections start out as small light green spots visible on the upper surface gradually turning brown to reddish-tan as infected tissue dies (Figure 1). Small, black, pimple-like bodies (pycnidia) develop inside the spot or lesion, usually arranged in a loose ring just inside the dark brown edges of the spot (Figure 1). Spores of the fungus are formed within pycnidia, and are released and splashed around during rainfall periods. Leaves remain susceptible as long as they are expanding and the size of leaf lesions indicate when, during expansion, the leaf was infected. For example, small lesions result when leaves become infected near the end of their expansion. Large lesions indicate the leaf was infected early in expansion. However, numerous small lesions, when clustered, may coalesce to damage large portions of the leaf. The death of large portions of the leaf blade may cause the entire leaf to die and abscise, but this is rare. On petioles, black, elongated lesions may induce wilting or abscission of leaves. Infections on berries initially appear as small, tan spots that develop a dark outer ring and expand rapidly to rot the entire berry. The brown berry shrivels into a hard, black, wrinkled mummy studded with spore producing pycnidia (Figure 2). Once the caps come off during bloom, berries of most varieties are highly susceptible for about 3-4 weeks, gradually developing resistance 5-6 weeks after capfall. Infections that take place during peak susceptibility generally show symptoms within 10-14 days. As berries develop resistance to black rot, the time for infections to become manifest takes longer, and infections that occur toward the end of the susceptibility period (second half of July?) may not develop symptoms until veraison.

Fig. 1 Development of black rot lesions on grapevine leaf (Concord).

 

Fig. 2 Development of black rot lesions on grape berry (Concord).

On shoots, lesions appear as elongated or elliptical brown cankers. Pycnidia may be clumped in the center of the lesion and/or line the margins of the lesion (Figure 3). These pycnidia produce spores during the current season and can be a source of further infection to fruit. These lesions remain on the shoots after they have “hardened off” and can survive over winter to release spores again the following spring. Large shoot lesions may render the shoots susceptible to breakage by wind, but this is rare.

Fig. 3 Black rot shoot lesions (Concord).

As berries develop resistance, the appearance of new infections may change: circular lesions are black, expand more slowly, and may remain small, often failing to affect the entire berry (Figure 4). Likewise, leaf infections that take place at the very end of the susceptibility/expansion period may become manifest as small dark pinhead size spots that do not expand (Figure 4).

Fig. 4 Limited black rot lesion development from infections occurring toward the end of the susceptibility period (Concord).

Cultural and chemical control:

The black rot pathogen survives the winter in infected grape tissue (primarily fruit mummies) which serves as a source of inoculum (spores) the following season.  Inoculum that remains in the trellis poses a much greater risk than inoculum dropped to the ground. Therefore, one of the most important methods of cultural control of black rot is removal of infected material, particularly fruit and cluster material, from the trellis. Once on the ground, mummy viability is reduced to further improve control. To take matters a step further, row middles can be plowed and hilling up under the row can bury mummies directly under vines. Maintaining an open canopy where fruit and other susceptible tissue dry out as quickly as possible after rainfall, will also help reduce this disease and improve fungicide penetration and coverage of the fruit.

Chemical control options for black rot mostly include two modern active ingredient classes like the strobilurins (azoxystrobin, kresoxim-methyl, pyraclostrobin, trifloxystrobin) and the sterol inhibitors (tebuconazole, tetraconazole, difenoconazole, myclobutanil) as well as the old standards like captan, mancozeb, and ziram. All are quite effective. The strobilurins and sterol inhibitors are more rainfast than the old standards and the sterol inhibitors have the capacity to stop the progress of an existing infection if applied within about 3 days after the infection period.

Scouting can be an important part of a black rot control program. The presence of pre-bloom leaf infections, especially those in the fruit zone, may indicate the presence of an over-wintering source of inoculum in the trellis and high risk of fruit infection after capfall. Fruit infections can occur during bloom and anytime up to 5-6 (native varieties) to 7-8 (Vitis vinifera) weeks after bloom.

In most parts of Pennsylvania, downy mildew first became active during the second half of May; at about the 5-6 leaf stage of grapevine development. Up here along the southern shore of Lake Erie, our first infection period occurred on May 25 (rainfall with temperatures above about 52 F) and first symptoms were observed at our farm on unprotected suckers of Chardonnay on June 1 (about 6-7 days after infection). On leaves, the first infections of downy mildew appear as yellowish ‘oil spots’ on the top of the leaf that coincide with a white, fluffy or downy patch of sporulation on the lower surface. On young shoots and clusters, early symptoms may first cause cluster rachises and shoots to thicken and curl (Figure 5).  As the pathogen, Plasmopara viticola, aggressively colonizes young, expanding grape tissue, infected shoots, clusters, and leaves may turn brown and die. When berries are infected later in the season their development is hindered and they fail to soften at veraison, turning a pale mottled green (white varieties) to red or pink (red varieties, Figure 6). Inflorescences and fruit clusters are most susceptible from about 2 weeks pre bloom to about 2 weeks post bloom. Highly susceptible varieties will require protection through 3-4 weeks post bloom because cluster stem tissue may remain susceptible until later in the season (after fruit have already become resistant) and cluster stem infections can still result in fruit loss. Young leaves and shoots are very susceptible, but become somewhat more resistant as they mature.

Fig. 5 Infection of downy mildew on young cluster and shoot showing curling and thickening of diseased tissue (Chancellor). The white sporulation after a warm humid night can be striking.

 

Fig. 6 Berries of red varieties (Concord (left) and Chancellor (center) at harvest) often turn red or pink after infection and fail to soften and develop properly. Late season leaf infections (far right photo) are yellowish to reddish brown and appear angular or blocky.

Cultural and chemical control:

Because the first inoculum arises from the vineyard soil, cultivation in early spring can help to bury over-wintering inoculum in old leaves and clusters on the ground, reducing primary inoculum in spring (much like with black rot). The first infections in spring often occur on shoots and sucker growth near or on the ground, and prompt elimination of this tissue can delay the occurrence of the first infections in the canopy. Also, the maintenance of an open canopy, where fruit and other susceptible tissue dry out as quickly as possible after rainfall and dew, will help minimize disease development.

There are many chemical options for downy mildew control and the best materials should be applied around and shortly after bloom. Active ingredients found in Ridomil, Zampro, Presidio, and Revus (and Revus Top) have been most effective on downy mildew in our trials. Where strobilurins are still working on this disease (no resistance yet), Abound (except in Erie county), Pristine, and Reason have been very effective too. The phosphorus acid formulations like Phostrol, Prophyt, and Rampart to name a few, have also been very effective against downy mildew, but generally cannot be expected to provide good control beyond 10 days after application, especially under high disease pressure. A tank mix of Ranman (cyazofamid) and phosphorus acid has been shown to be very effective on downy mildew in many university trials. All these aforementioned materials are very rainfast. In addition to these fungicides are the old standards that are strictly surface protectants and are more subject to removal by rainfall. A mancozeb product is probably the best among this group, but fixed copper fungicides can also be quite effective against downy mildew on varieties that are not sensitive to copper. Ziram and captan can also be part of an effective downy mildew program, but are somewhat less effective than mancozeb.

Powdery mildew is caused by the fungus Uncinula necator.  Infection on leaves appears mainly on the upper surface as white, powdery patches, though the undersides of leaves can also become infected (Figure 7). As the leaf surface becomes covered with the fungus, leaf function (and photosynthesis) is impaired, with varieties of V. vinifera and highly susceptible French hybrids being most severely affected. Infection by U. necator can stunt growth of new tissues and severe infection of young expanding leaves often results in cupping and distortion of leaves. Cluster infections around bloom may lead to poor fruit set, while later infection can cause berry splitting.

Fig. 7 Powdery mildew on young, developing ‘Concord’ berries.

Though primary infections in spring (at least 0.1″ rainfall and greater than 50 F) require rainfall for spore release, secondary disease cycles that result from primary infections, do not require rainfall.  Under optimum weather conditions (temperatures in the mid 60s to mid 80s F) secondary disease cycles can be repeated every 5 to 7 days, allowing for explosive increase of disease in the vineyard, especially in highly susceptible wine varieties. Note that optimum temperatures for the fungus are the norm through most of the summer in Pennsylvania and that starting around bloom, nearly every day is an infection period, rain or shine.

In most grape varieties, berries are highly susceptible to infection from the immediate pre-bloom stage until about 2-3 weeks after fruit set, and efforts to protect fruit with fungicides should concentrate on this critical period with timely applications every 7-14 days. Cluster rachises and leaves remain susceptible until harvest and their need for continued protection depends on varietal susceptibility, crop size, and weather. For example, after the fruit susceptibility period, further management of leaf and rachis infections may not be necessary on Concord and other native juice varieties unless vines are heavily cropped or ripening conditions are poor.  On the other hand, V. vinifera and susceptible hybrids, may require management of foliar mildew until at least veraison or beyond.

Cultural and chemical control:

There are cultural considerations that can reduce opportunities for powdery mildew disease development.  Most involve limiting humidity and promoting sun exposure to all parts of the vine. For example, a training system that improves air movement through the canopy, prevents excess shading and humidity and promotes fungicide penetration to the cluster zone which will help reduce powdery mildew development. Sunlight is lethal to powdery mildew and regular exposure of leaves and fruit can greatly reduce mildew development. Good weed control can also minimize humidity levels that contribute to mildew development.

Unfortunately, cultural measures can only serve as an enhancement to a chemical control program in Pennsylvania and other parts of the northeast. However, we have many effective fungicides for powdery mildew that can provide high levels of control through the critical period around bloom: Vivando, Quintec, Luna Experience, Endura, and now Aprovia. Aprovia is also labeled for black rot control, but our recent tests have indicated that Aprovia’s black rot efficacy is limited especially under high disease pressure on susceptible varieties. The difenoconazole products (Revus Top, Quadris Top, Inspire Super) can also be very effective on powdery mildew, though they may best be used outside the critical two spray period around bloom. Be aware that difenoconazole has been found to cause injury to Concord and a few other varieties (read the label). Sulfur can be an effective powdery mildew material too (on sulfur tolerant varieties) and many wine grape growers rely heavily on it, especially as a tank mix pre-bloom with mancozeb for all diseases. However, it is not recommended as a ‘stand-alone’ material during the critical fruit protection period for powdery mildew control.

There are lots of ‘alternatives’ for powdery mildew control that may be appropriate for late season sprays (to maintain a clean vineyard) that may gradually be used to replace the sulfur and/or synthetics or rotate with synthetics, particularly for reds where late sulfur applications can create wine quality issues. These are materials for which there is little risk of the development of resistance. In fact, these materials can be used to manage the development of resistance to our more risky synthetic fungicides mentioned earlier. Petroleum based oils like JMS Stylet-oil are very effective at 1-2 % solution, but excessive use late in the season (do not apply around or after veraison) may limit sugar accumulation and fruit maturity.  And, oils should not be tank mixed with sulfur or applied within 14 days of a sulfur-containing fungicide application. Copper, is moderately effective on powdery mildew and generally applied with lime to reduce the risk of phytotoxicity (read the label). Like sulfur, copper fungicides should not be applied under slow drying conditions as this increases the chance for plant injury. Other materials include potassium bicarbonates such as Kaligreen, Armicarb O, and Milstop.  These materials generally produce modest results, and are most effectively applied at short intervals (7 days) to achieve satisfactory control on susceptible varieties.  Again, these materials are not appropriate for the critical fruit protection period, but are best integrated during the early season when disease pressure is low OR after the critical fruit protection period to help control leaf infections.

Phomopsis cane and leaf spot is caused by the fungus, Phomopsis viticola. Earlier this spring, growers in many parts of Pennsylvania experienced problems with Phomopsis development on new shoots and leaves. Prolonged wetting/rainfall during the first week of May led to widespread infection by this pathogen on Concord in the Lake Erie region; virtually every shoot of every vine in every Concord vineyard we have examined has some level of Phomopsis development on the first one or two internodes. The infection period(s) occurred when shoots were in the 1-3″ range and inflorescences were just becoming exposed. In some cases, heavy infection of inflorescences is likely to result in problems with fruit rot after veraison (months after the infection period took place!). Fruit are generally at risk of new infections until a couple weeks or so after bloom, but infections of the cluster stem tissue that occur in the early pre-bloom period can move into berries during ripening and cause fruit to rot and shell before harvest. The concentration of heavy infection at the base of the oldest internodes, may result in large scabby areas that weaken the shoot (Figure 8) and green shoots that are severely infected are more apt to break under windy conditions. Leaf infections appear as pinhead sized black spots surrounded by a yellow halo (Figure 9). These infections appear to be of little consequence, other than revealing the presence of the pathogen. Lesions on cluster stems are black and sunken, and can girdle parts of the cluster rachis causing the cluster or parts of the cluster to break off or shrivel.

Fig. 8 Numerous lesions concentrated at the base of the oldest internodes result in larger scabby areas that weaken the shoot.

 

Fig. 9 Leaf infections of Phomopsis cane and leaf spot on Concord grape.

When berries are infected, they can remain symptomless until ripening when they turn brown and become studded with small pimple-like fruiting structures of the fungus (Figure 10) often resembling black rot infected berries.

Fig. 10 Phomopsis fruit rot on ripe Vignoles and Niagara grapes.

However, even though direct fruit infection by both pathogens can occur during the same peak susceptibility period (bloom through 3-4 weeks after bloom), black rot fruit rot symptoms become observable while berries are still green, whereas Phomopsis fruit infections lay dormant until after ripening. Also, leaf symptoms of these two diseases are very different from each other and can be used to determine which pathogen(s) are present and most likely to have caused disease on nearby fruit.

Cultural and chemical control:

Hand pruning to remove dead wood and pruning stubs from the trellis removes much of the over-wintering inoculum of Phomopsis. For this reason, cane pruning can reduce the disease compared to a cordon system that retains a maximum amount of older wood. Trellis systems that train shoots upward also reduce infections on the oldest shoot internodes and clusters. And of course, the maintenance of an open canopy where fruit and other susceptible tissue dry out as quickly as possible after rainfall, will help minimize disease development.  For wine grapes, fruit zone leaf removal and shoot thinning reduce canopy density, hasten drying after rainfall, and improve fungicide penetration and coverage of the fruit.

Phomopsis management with fungicides should continue through the first or second post bloom spray, after which inoculum of the fungus is generally spent. Strobilurins, mancozeb products, Captan, and Ziram are generally the only effective materials for Phomopsis control. Some formulations of sterol inhibitor fungicides claim Phomopsis control, but their level of efficacy is still under question and would not be recommended for management of this disease.

 

Much of the information in this blog can be found in the 2017 New York and Pennsylvania Pest Management Guidelines for Grapes. Be sure to get your copy through Cornell University press. You can also read the publication; Disease Management Guidelines for Organic Grape Production in the Lake Erie Region found online at http://agsci.psu.edu/research/ag-experiment-station/erie/research/plant-pathology/organic-grape-disease-management-trials/DiseaseMgmtGuidelines07.pdf which contains much of the information discussed in this blog.

 

References:

2017 New York and Pennsylvania Pest Management Guidelines for Grapes. Edited by Tim Weigle and Andy Muza. Cornell and Penn State University Cooperative Extension.

Hoffman, L.E., W.F. Wilcox, D.M. Gadoury and R.C. Seem. 2002. Influence of grape berry age and susceptibility to Guignardia bidwellii and its incubation period length. Phytopathology 92:1068-1076.

Hoffman, L.E., W.F. Wilcox, D.M. Gadoury, R.C. Seem, and D.G. Riegel. 2004. Integrated control of grape black rot: Influence of host phenology, inoculum availability, sanitation, and spray timing. Phytopathology 94: 641-650.

Grape Leafhoppers

By: Andy Muza, Penn State Extension – Erie County

There are several species of leafhoppers in the genus Erythroneura that feed on grape foliage. Research conducted in New York showed that the eastern grape leafhopper Erythroneura comes (Say) is the most common on American varieties (e.g., Concord, Niagara) while E. bistrata/vitifex complex were more common on Vitis vinifera and interspecific hybrids. Other species found in commercial grapes included E. tricinta, E. vulnerata and E. vitis. (1). Regardless of which of these species is prevalent, their life cycles are similar and the injury caused by these leafhoppers and their management is the same.

Life Cycle and Description

The various Erythroneura leafhoppers overwinter as adults in leaf litter in the vineyard or in plant debris around the vineyard. As temperatures increase in the spring, adults begin feeding on a variety of weeds, bushes and trees. Adults then migrate into vineyards to feed when leaves emerge (2). Eastern grape leafhopper adults are small (only about 1/8”), white-pale yellow, with darker lemon colored markings on the wings, and 3 black spots towards the posterior portion of the wings (Figures 1 & 2).  Other Erythroneura species have varying coloration and markings (3).

 

Figure 2. Adult grape leafhoppers on underside of Concord leaf. Photo: Andy Muza, Penn State.

Initial feeding occurs on sucker growth and basal leaves on shoots in the trellis. Females lay eggs on the undersides of leaves just below the leaf surface. Nymphs of the first generation hatch in mid-late June. Immatures are wingless, pale yellow in coloration with tiny wing pads (Figure 3). Nymphs develop through 5 instars with wings fully developed after the fifth molt (2). Nymphal development to adulthood takes about 30 days or less depending on environmental conditions. In northwestern Pennsylvania nymphs of the second generation can be found in vineyards in mid-late August. There are 1.5 – 2 generations/season in the Lake Erie Region, depending on seasonal temperatures, and in the southwestern portion of the state likely 2.5 – 3 generations.

Grape leafhopper (GLH) adults and nymphs have piercing – sucking type mouthparts and feed on the underside of leaves extracting the contents of leaf cells resulting in white – yellow spotting of the foliage (stippling). Moderate – Heavy feeding causes yellowing and browning of tissue while severe injury can result in premature defoliation (Figure 4).

Figure 4. Concord leaf with stippling and browning of leaf tissue caused by GLH feeding. Photo: Andy Muza, Penn State.

Management

The greatest risk for economic losses due to grape leafhopper (GLH) feeding occurs during hot, dry years in vineyards with heavy crop loads and high leafhopper populations (4). In most years, the majority of vineyards in Pennsylvania should not require an insecticide treatment specifically for management of grape leafhopper. Therefore, routine, prophylactic insecticide treatments for leafhoppers are unnecessary and not recommended. Insecticide applications should be based on scouting information and threshold levels.

Scouting – Tim Martinson at Cornell designed a scouting procedure for leafhoppers which corresponds to the timings when sampling for grape berry moth injury are conducted (5).

10 Days Postbloom – Usually population levels and feeding is minimal at this time of the season. If however, early in the season, high numbers of adult leafhoppers migrate into the vineyard this can result in enough leaf feeding to reduce bud fruitfulness in the following year (4). Scouting should be conducted to look for leaf feeding on interior leaves in the canopy. If leaf stippling is noticeable throughout the vineyard then an insecticide application is recommended.

Third week in July – Check 4 different areas in the vineyard (2 exterior and 2 interior). At each area look at lower leaves on shoots and check for leaf feeding. If no – minimal injury is observed, proceed to the next sampling site (Figure 5). If moderate-heavy leaf stippling is observed then begin counting nymphs on the undersides of leaves (Figure 6). Examine 5 leaves (leaves 3-7 from base of shoot)/shoot on 5 different shoots at each location. If a threshold of 5 nymphs/leaf is reached then an insecticide application is recommended.

Figure 5. Minimal GLH stippling on Concord leaf. Photo: Andy Muza, Penn State.

 

Figure 6. GLH nymphs, cast nymphal skins and adults on underside of leaf. Photo: https://ecommons.cornell.edu/bitstream/handle/1813/43102/grape-leafhopper-FS-NYSIPM.pdf?sequence=1&isAllowed=y

Late August – The scouting protocol at this time follows the same procedure as the July sampling. However, the threshold for the August sampling period is 10 nymphs/leaf before an insecticide application is recommended.

Based on scouting data, if an insecticide application becomes necessary during the season, there are a number of options available. Consult the “2017 New York and Pennsylvania Pest Management Guidelines for Grapes” (6) for a list of insecticides which are effective for grape leafhopper management.

Shoot and leaf removal practices conducted in many wine grape vineyards may reduce leafhopper population levels, if the removed leaves are harboring nymphs of this pest. In addition, these practices will open up the canopy for better spray penetration.

A number of predators (e.g., spiders, green lacewings, lady beetles, etc.) and egg parasitoids (Anagrus species) which occur in vineyards contribute to reducing leafhopper population levels (7). Therefore conserving these beneficial insects, by avoiding unnecessary applications of broad spectrum contact insecticides, is advised. Good weed control in the vineyard and the prevention of overgrown areas around the vineyard will also reduce leafhopper overwintering sites.

References

  1. Martinson, T. E. and T. J. Dennehy. Varietal Preferences of Erythroneura Leafhoppers (Homoptera: Cicadellidae) Feeding on Grapes in New York. Environ. Entomol. 24:550-558 (1995). https://academic.oup.com/ee/article/24/3/550/2394852/Varietal-Preferences-of-Erythroneura-Leafhoppers
  2. Grape Leafhopper. Grape Insect IPM Insect Identification Sheet No. 4 (1984). NYS. Ag. Exp. Station, Cornell University. https://ecommons.cornell.edu/bitstream/handle/1813/43102/grape-leafhopper-FS-NYSIPM.pdf?sequence=1&isAllowed=y
  3. Leaf- Stippling Leafhoppers (Ontario GrapeIPM). Ontario Ministry of Agriculture Food & Rural Affairs, Canada http://www.omafra.gov.on.ca/IPM/english/grapes/insects/ls-leafhoppers.html
  4. Martinson, T. E., et al. Impact of Feeding Injury by Eastern Grape Leafhopper (Homoptera:Cicadellidae) on Yield and Juice Quality of Concord Grape. Am. J. Enol. Vitic., 48:291-302 (1997). http://www.ajevonline.org/content/ajev/48/3/291.full.pdf
  5. Martinson, T. E., et al. Risk Assessment of Grape Berry Moth and Guidelines for Management of the Eastern Grape Leafhopper. New York’s Food and Life Sci. Bull. 138. 10 pp. (1991). http://nysipm.cornell.edu/publications/grapeman/files/risk.pdf
  6. Weigle, T. H., and A. J. Muza. 2017. “2017 New York and Pennsylvania Pest Management Guidelines for Grapes”. Cornell and Penn State Extension. 150 pp. https://store.cornell.edu/p-197039-2017-new-york-and-pennsylvania-pest-management-guidelines-for-grapes.aspx
  7. Williams, L., III, and T. E. Martinson. 2000. Colonization of New York Vineyards by Anagrus spp. (Hymenoptera:Mymaridae): Overwintering Biology, Within-Vineyard Distribution of Wasps, and Parasitism of Grape Leafhopper, Erythroneura spp. (Homoptera: Cicadellidae), Eggs. Biol. Control 18:136-146.   https://pubag.nal.usda.gov/pubag/downloadPDF.xhtml?id=43140&content=PDF

Early season grapevine canopy management, Part II: Early leaf removal (ELR)

By:  Maria Smith and Dr. Michela Centinari, Dept. of Plant Science

In the previous post, we discussed shoot thinning as a method to achieve vine balance and improve the canopy microclimate (Part I: Shoot Thinning). In this post, we will discuss the use early leaf removal (ELR), a canopy management practice implemented around bloom.  ELR primarily serves to reduce the severity of Botrytis bunch rot infection in susceptible varieties (Wines and Vines:  Benefits and Costs of Early Leaf Removal), but may also be an effective practice for reducing crop yield.

ELR is currently considered an experimental canopy management practice for vineyards.  While it shows great promise within the research and Extension literature (1, 2, Cornell Cooperative Extension 2016), Penn State Extension does not currently recommend implementing ELR as a replacement for traditional methods (i.e., cluster thinning, fungicide sprays) for yield and rot control. However, growers curious about the effects of ELR may find it useful as a supplementary canopy management practice, especially for disease management and crop reduction.

Throughout this post, we will discuss the effects of ELR on:

  • Crop level in highly-fruitful varieties that produce a high number of clusters (3-4 per shoot) or large clusters such as vinifera cvs. Grüner Veltliner, Sangiovese, and Barbera.
  • Botrytis bunch rot infection.
  • Fruit and wine composition.

What is Early Leaf Removal (ELR) and how does it work?

ELR is the removal of basal leaves of the main shoots and, optionally, lateral shoots developed from the basal nodes (http://gph.is/2r3ZLc0; Figure 1).

Screenshot 2017-06-01 12.31.36

ELR is typically performed shortly before (pre-bloom) or at the beginning of bloom (trace-bloom; Figure 2A). In some cases, however, it has been performed later during full-bloom or at the onset of fruit-set (Figure 2B).

Screenshot 2017-06-01 12.31.48

Before and during bloom, the oldest basal leaves have a major role in providing carbohydrates (e.g., sugars) to support the growing shoot and inflorescence (i.e., flower clusters). In contrast, young leaves on the middle and top part of the shoot are still developing and not very photosynthetically ‘active’ at this time (3).  Literature suggests the removal of basal leaves at bloom may starve the inflorescence for a carbohydrates food source (4).  The lack of carbohydrate resources reduces fruit-set (i.e., the percentage of flowers that will develop into berries), which likely reduces the number of berries per cluster at harvest (5). When ELR is performed later, at the onset of fruit-set, removing basal leaves may induce a reduction in berry size and an increase in berry abscission due to carbohydrate limitation at the onset of fruit development (6). Therefore, yield reduction achieved with ELR is the result of reduced cluster weight (reduced number of berries per cluster and/or reduced berry weight). In contrast, yield reduction achieved by cluster thinning is the result of a reduced number of clusters per vine.

Why are ELR practices currently under research investigation?

An increased number of studies is investigating the use of ELR as a potential alternative to cluster thinning techniques used for crop yield control in highly-fruitful wine grape varieties (5, 6, 7). As opposed to traditional cluster thinning, ELR can be more easily mechanized. (Author’s note:  for more information on mechanization, see Additional Resources at the bottom of the post.) ELR may additionally confer benefits such as:

  1. Reduced severity of Botrytis rot infection

Cluster compactness, or the tightness of berries on the cluster, has been positively related to the severity of Botrytis bunch rot infections (8). It is suggested that more compact clusters experience more rot. ELR decreases cluster compactness by reducing the number of berries per cluster and/or the berry size. Decreased cluster compactness through implementing ELR has reduced Botrytis rot infections in several tight-cluster varieties such as Pinot Noir, Riesling, Chardonnay, and Vignoles (1, 9, 10, 14). As an additional benefit, the removal of basal leaves increases sunlight penetration and air movement in the fruiting zone, which is important for improving spray penetration within the canopy (2016 Post Bloom Disease Management Review).

  1. Improved fruit and wine composition

ELR has consistently been reported to alter fruit composition, particularly for red Vitis vinifera varieties in Mediterranean climates (Tempranillo, Sangiovese, Barbera, etc.; 2, 5, 6, 12). In several instances, fruit harvested from ELR vines had higher levels of total soluble solids (TSS, °Brix), phenolic compounds (e.g., flavonols), and total anthocyanins compared to un-defoliated vines (2, 11, 12). ELR can also reduce methoxypyrazines, ‘herbaceous’ aromas found in higher concentrations among immature grapes at harvest, and may contribute to improved wine color intensity (13).  ELR may alter three important parameters associated with berry development and ripening (2):

  • Decreased berry size – Smaller berries tend to have greater skin-to-pulp ratio and higher concentrations of desirable phenolic and aroma compounds which are mainly present in the skin.
  • Increased leaf area-to-yield ratio on a per shoot basis – A greater leaf area-to-yield ratio may translate into higher sugar produced per shoot. More sugar availability could contribute to better fruit ripening.
  • Improved canopy microclimate – ELR, like traditional leaf removal, improves the microclimate of the fruiting zone through decreased leaf density and increased sunlight penetration to the fruit. Higher temperatures coupled with increased sunlight exposure in the fruiting zone can be especially important under cool or cloudy ripening conditions, as they may accelerate berry ripening, resulting in higher TSS, decreased malic acid, increased anthocyanin concentration, and degradation of green volatile aroma compounds such as methoxypyrazines that may mask fruity or floral aromas. Higher ultraviolet (UV) radiation in the fruiting zone in response to increased sunlight penetration may increase production of flavonols, as flavonols biologically act to protect berries from UV exposure (3, 11). Flavonol compounds along with anthocyanin influence red wine color and are used as determinants of quality in fruit (11).

It is important to keep in mind that yield reduction is not desirable in all grape varieties. The use of ELR with varieties that do not typically over-crop may result in under-cropped situations with potential negative effects on fruit quality and vine health, in addition to unnecessary yield reductions and thus revenue loss.

How many leaves should be removed to induce yield reduction?

Unfortunately, there is no “one size fits all” number of leaves to remove when implementing ELR as a vineyard management practice.  The required number of leaves removed to significantly reduce yield through reduced fruit-set depends on several factors, including shoot length and the shoot leaf area at the time of removal. For example, by pulling 5 basal leaves on a shoot with only 8 leaves at trace-bloom, we would remove about 63% of the total number of leaves.  The percentage of leaf area removed would be even higher as the remaining leaves at the top of the shoot are much smaller than those removed from the bottom of the shoot. In contrast, a longer shoot with 15 leaves total will only lose 33% of the leaf area when 5 basal leaves are pulled. Thus, removing 5 leaves from a short shoot would have a more severe effect of depriving the inflorescence of sugar resources than removing the same number of leaves on long shoots (Figure 3).

Screenshot 2017-06-01 12.32.01

Sometimes the degree of ELR is severe in order to induce a yield reduction commensurate with the more traditional cluster thinning technique. For example, Pinot Noir grown in southwestern Michigan showed a reduction in yield from 6.1 tons per acre in non-defoliated vines to 3.6 tons per acre when about half (8 out of 15) of the leaves on the shoots were removed (1). This was a 40% reduction in yield. Comparatively, when 4 or 6 leaves were removed from the Pinot Noir, no significant effect was found in crop yield (1).

With the high potential for crop yield reduction, Dr. Michela Centinari’s lab has been experimenting with ELR for the past two years. We have been examining the effects of ELR at trace-bloom on Grüner Veltliner (V. vinifera) grown in Central Pennsylvania. Grüner Veltliner is highly fruitful, typically producing 2-3 large clusters per shoot. In our experimental practices, we removed 5 basal leaves at trace-bloom. Our objective was to compare the use of ELR to cluster thinning for crop yield reduction. Our first year of data found that the implementation of ELR decreased yields by only about 15% (10.7 tons per acre in the non-defoliated control to 9.3 tons per acre in defoliated vines). In comparison, vines thinned to 1 cluster per shoot had a 45-50% reduction in yield compared to the un-thinned control (10.7 tons per acre to 6.5 tons per acre).

This suggests that a greater leaf removal intensity may be needed for this variety to produce yield reduction comparable to cluster thinning, and we are currently testing different intensity levels of trace-bloom ELR to evaluate if the amount of leaf area removed correlates with reduction of fruit-set and yield at harvest.

Again, ELR is still considered an experimental canopy management technique. For those growers growing high yielding varieties and looking to reduce crop level, cluster thinning is still the recommended practice. For more information on how to implement appropriate CT techniques, please see Cornell Cooperative Extension Fruit thinning in wine grapes and Crop thinning: cluster thinning or cluster removal.

Considerations regarding ELR

Other factors to consider if you are interested in applying ELR:

  • Fruit-set percentage – One of the factors facing the unpredictability of ELR is the weather conditions between bloom and fruit set. Since weather can have a large effect on the percentage of fruit-set (Fruit set in grapes 101), ELR may potentially exacerbate ‘poor’ fruit-set if extended periods of wet, cool (< 59°F), overcast, or very hot (> 90°F) weather conditions occur following leaf removal.  Additionally, berry sunburn may be a potential concern with ELR when performed under chronic high light and temperature intensity.
  • Bud Fruitfulness – While it is generally acknowledged that increased sunlight exposure is positive for bud development, a potential reduction in bud fruitfulness (number of clusters per shoot) may occur in the following season as a result of bud damage from ELR (14). Although still uncertain, bud damage may be the result of physical damage during leaf removal and/or reduction of carbohydrate supply during bud development.
  • Carbohydrate Storage in Cool Climate Grown Vines – Carbohydrates are the main energy source for grapevine growth, stress defense, and fruit ripening. Post-harvest carbohydrate storage in perennial tissues is a determinant of vine overwinter survival and is fundamental for shoot development in the following season. Removing leaves during ELR may alter the amount of carbohydrates produced by the leaves over the season and how carbohydrates are distributed among the vine organs. Currently, limited information is available on how ELR affects carbohydrates storage in perennial tissues and how this relates to dormant tissue (buds and canes) cold hardiness. This is a point of current interest to Centinari’s lab at Penn State, with current research being conducted in vinifera and hybrid wine grape varieties.
  • Crop Estimation – Yield predictions based on ELR use is currently not available. In this regard cluster thinning is a more conservative approach. Unlike ELR, which is performed very early in the season, cluster thinning severity can be decided upon estimation of final yield.

 

Summary

ELR holds potential as a way to reduce yield and Botrytis rot infection for some grape varieties grown in the Mid-Atlantic and other cool-climate regions. However, more research is needed to better understand the consistency of ELR practices on vine physiology, yield reductions, and fruit quality. Current efforts are on-going by the Centinari lab and Bryan Hed at the Lake Erie Grape Regional Extension Center (LEGREC) to evaluate the use of manual and mechanized ELR in hybrid and V. vinifera varieties across Pennsylvania.

Additional Resources

PSU Wines and Grapes blogs:  An Overview of Cluster-Zone Leaf Removal Strategies for Cool Climate Vineyards and 2016 Post Bloom Disease Management Review

Intrieri C, Filippetti I, Allegro G, et al. 2008.  Early defoliation (hand vs mechanical) for improved crop control and grape composition in Sangiovese (Vitis vinifera L.).  Aus. J. Grape Wine Res. doi: 10.1111/j.755-0238.2008.00004.x

References Cited

  1. Acimovic D, Tozzini L, Green A, et al. 2017. Identification of a defoliation severity threshold for changing fruitset, bunch morphology and fruit composition in Pinot Noir.  J. Grape Wine Res. doi:  10.1111/ajgw.12235
  2. Bubola M, Sivilotti P, Janjanin D, and Poni S.   Early leaf removal has larger effect than cluster thinning on cv. Teran grape phenolic composition.  AJEV.  doi: 10.5344/ajev.2016.16071
  3. Illand P, Dry P, Proffit P, and Tyerman S. Photosynthesis. In The Grapevine, from the science to the practice of growing vines for wine. pp. 91-107.
  4. Coombe BG.   The effect of removing leaves, flowers and shoot tips on fruit-set in Vitis vinifera L. J. Hortic. Sci. 37:1-15.
  5. Poni S, Casalini L, Bernizzoni F, et al. 2006. Effects of early defoliation on shoot photosynthesis, yield components, and grape composition. AJEV. 57: 397-407.
  6. Tardaguila J, Martinez de Toda F, Poni S, and Diago MP. 2010. Impact of early leaf removal on yield and fruit and wine composition of Vitis vinifera Graciano and Carignan. AJEV. 61(3):372-381.
  7. Silvestroni O, Lanari V, Lattanzi T, et al. Impact of crop control strategies on performance of high-yielding Sangiovese grapevines. AJEV. doi: 10.5344/ajev.2016.15093
  8. Vail ME and JJ Marois. 1991. Grape cluster architecture and the susceptibility of berries to Botrytis cinerea. Phytopathology 81:188-191.
  9. Sternad Lemut M, Sivilotti P, Butinar L, et al. Pre-flowering leaf removal alters grape microbial population and offers good potential for a more sustainable and cost-effective management of a Pinot Noir vineyard. J. Grape Wine Res. doi: 10.1111/ajgw.12148
  10. Hed B, Ngugi HK, and Travis JW.   Short- and long-term effects of leaf removal and gibberellin on Chardonnay grapes in the Lake Erie region of Pennsylvania. AJEV.  66(1): 22-29.
  11. Moreno D, Vilanova M, Gamero E, et al. Effects of preflowering leaf removal on phenolic composition of Tempranillo cv. in semi-arid terroir of western Spain.  AJEV. doi: 10.5344/ajev.2014.14087
  12. Risco D, Pérez D, Yeves A, et al. Early defoliation in a temperate warm and semi-arid Tempranillo vineyard: vine performance and grape composition. Aus J Grape and Wine Res. doi: 10.1111/ajgw.12049
  13. Sivilotti P, Herrera JC, Lisjak K, et al. 2016. Impact of leaf removal, applied before and after flowering, on anthocyanin, tannin, and methoxypyrazine concentrations in ‘Merlot’ (Vitis vinifera) grapes and wines. J. Agric. Food Chem.  64:4487-4496.
  14. Sabbatini P, and Howell GS. 2010. Effects of early defoliation on yield, fruit composition, and harvest season cluster rot complex of grapevines.  HortScience 45(12):1804-1808.

Maria Smith is a viticulture PhD candidate with Dr. Michela Centinari in the Department of Plant Science.  She specializes in cold stress physiology of wine grapes.  She was the previous recipient of the John H. and Timothy R. Crouch Program Support Endowment, an endowment founded and funded by the Crouch brothers, original owners of Allegro Winery in Brogue, PA.  She is currently funded by the Northeast Sustainable Agriculture Research and Education (NE-SARE) program, a program from the USDA National Institute of Food and Agriculture (NIFA).

 

Early season grapevine canopy management, Part I: Shoot thinning

By: Maria Smith and Dr. Michela Centinari, Dept. of Plant Science

This is the first of two posts on grapevine canopy management in the early growing season from bud burst to bloom.  The second in the series will be post in two weeks and will focus on pre- or trace-bloom leaf removal for crop level and disease pressure control.

This week, our blog post will focus on shoot thinning, the first canopy management practice of the growing season.  As seen in the pictures below, we spent last week shoot thinning Grüner Veltliner (V. vinifera) vines in a central Pennsylvania vineyard (Figure 1).

Figure 1. (A) Andrew Harner, graduate student at Penn State in the Centinari lab, is shoot thinning Grüner Veltliner (V. vinifera) vines, May 10, 2017, Lewisburg, PA. (B) Grüner Veltliner shoot length at the time of thinning (pencil as a reference for shoot length).

In the following sections, we will highlight the benefits and costs associated with shoot thinning while providing a few general shoot thinning guidelines for both V. vinifera and hybrid cultivars in the Mid-Atlantic region.

Benefits of Shoot Thinning Grapevines

While dormant pruning (https://psuwineandgrapes.wordpress.com/tag/dormant-pruning/) is the primary tool used by grape growers to maintain vine structure, canopy architecture and regulate crop level, shoot thinning provides an additional canopy management tool to bring vines into vegetative and fruiting balance by reducing shoot density and the number of clusters per vine. Cluster thinning later in the season may be needed in order to balance highly-fruitful vines.

In addition to improving balance between vegetative growth and fruit biomass, other benefits of shoot thinning include:

  • Reduction of canopy density and fruit shading: through removal of selected shoots, shoot thinning reduces overcrowding of shoots in the canopy thus reducing the number of leaf layers and improving sunlight exposure to fruit (1).
  • Reduction of disease pressure: reducing canopy density improves air circulation and sunlight penetration that promotes quicker drying of leaves and fruit, as well as increases spray penetration.

Timing of Shoot Thinning

Shoot thinning should be done early in the growing season, when shoots are approximately 5-6 inches long and not more than 10-12 inches long. Shoot thinning should be timed after the date of last ‘expected’ frost, such that secondary or non-damaged primary shoots can be retained in the event of a late spring frost.

When shoot thinning is performed before inflorescences are visible (shoots 0.8 inch to 4 inches), increased vigor of the remaining shoots and lateral shoot growth may occur as a response, negating the benefits of shade reduction (1). When performed too late (shoot longer than 10 inches), shoots become lignified at the base and difficult to remove.  If performing late thinning, pruning shears should be used if there is risk of damaging the arm of the vine. It also takes longer to thin longer shoots, potentially decreasing the cost-effectiveness of this practice.

Shoot Spacing and Density Recommendations

Generally, shoot thinning on cane-pruned vines is easier, faster, and more straight-forward than spur-pruned vines, which require substantially more decisions regarding what shoots to retain or remove, and where shoots should be spaced along the cordon (2; Figure 2).

Figure 2. Before shoot thinning: spur-pruned (left) vs. cane pruned (right) in Grüner Veltliner, May 26, 2016, Lewisburg, PA.

Plant genotype, soil, and climate are all factors influencing vine vigor potential and capacity to fully ripen a crop.  Therefore, these factors indirectly affect the appropriate number of shoots to retain at thinning.  Many Cooperative Extension websites provide recommendations on range of optimal shoot density based on cultivars grown in their region. [Author’s note: for the eastern US see the additional resources section at the bottom of the post.]

Shoot density targets for Pennsylvania regions:

  • For vinifera cultivars it is recommended to leave 3 to 5 shoots per linear foot of canopy (3, 4; Figure 3). The general rule of thumb is to retain fewer shoots in red varieties and more in white varieties. However, other factors (i.e., cultivar disease susceptibility) must be taken into consideration.

Figure 3. Suzanne Fleishman, graduate student at Penn State in the Centinari lab, is shoot thinning spur-pruned Grüner Veltliner vines (May 26, 2016). Note the differences shoot density between the cordons on the right (thinned) and on the left (unthinned) cordons.

  • For most of the hybrid cultivars it is recommended to leave 4 to 6 shoots per linear foot of canopy (5).
  • For Concord and other native cultivars, as many as 15 shoots per linear foot of canopy can be retained (4).
  • In divided canopies trellis systems, the same shoot density along each cordon should be retained (Figure 4).

In addition to the number, the position of the shoots along the cordon is important.  Ideally, the shoots retained should be equally spaced to promote a uniform, balanced canopy.

Figure 4. Proper shoot density at harvest on Gewurtztraminer vines trained on divided Scott-Henry system in Andreas, PA.

What types of shoots should you remove?

  • Weak, non-fruitful shoots especially if they grow in crowded areas of the canopy.
  • Secondary and tertiary shoots, if a primary healthy shoot has emerged.
  • Shoots arising from the trunk that are not retained for renewal wood (e., new trunks and canes or cordons).

Does shoot thinning improve fruit composition and wine sensory perception?

The associated costs with manual labor and labor shortages are reasonable considerations before implementing vineyard management practices.  This is also true for implementing shoot thinning techniques into a vineyard.  Nonetheless, it is also important to consider the potential benefits from implementing a new practice.

The effects of shoot thinning practices on hybrid varieties are a bit unclear. A previous study on shoot thinning found that shoot thinned Marechal Foch (red interspecific hybrid of Vitis) vines exhibited higher total soluble solids (ᵒBrix) and berry anthocyanin concentrations as compared to un-thinned vines (6). The increase in berry anthocyanin, however, did not translate into higher anthocyanin concentration in the final wine, and furthermore, shoot thinning did not impact the sensory perception of “fruitiness” of the wines (6). In contrast, a study focusing on Corot noir (red interspecific hybrid of Vitis) implementation of shoot thinning provided inconsistent results in grape and wine quality across a two-year (2008-2009) evaluation, which was determined by ᵒBrix, pH, titratable acidity (TA), wine anthocyanin, berry and wine tannin content (7).  Shoot thinning increased berry ᵒBrix, wine alcohol concentration and anthocyanin content only in second year of this study.  While berry TA at harvest was lower (e.g., 2008, un-thinned = 8.6 g/L, shoot thinned = 7.6 g/L), there were no differences in the TA of wine in either year (7).  Shoot thinning also decreased berry seed tannin in 2008 and berry skin and wine tannin in 2009, which could have negative implications for final wine, considering generally low tannin concentrations in hybrid red wines (7).  In an effort to compensate for costs associated with shoot thinning and yield loss, this study on Corot Noir suggested growers increase the price of grapes by 11 to 20% per ton, depending on the average annual market price and yield loss (7).

A study in Fayetteville (Arkansas) on three highly-fruitful French-American hybrid cultivars (Aurore, Chancellor, and Villard noir) found that shoot thinning increased fruit sugar accumulation (ᵒBrix) only in Chancellor and without changes in pH or TA, while a more intense juice color was associated with shoot thinned vines of both red cultivars (Chancellor and Villard noir; 8). In addition, shoot thinning favorably decreased the Ravaz index (yield to pruning weight ratio) for all three cultivars, improving vine balance (8).

The results of these studies suggest that in some situations the costs of shoot thinning may not outweigh the benefits, especially for hybrids that do not command a high market value (Finger Lakes Grape Prices 2016).  However, none of these studies account for potential reduction in disease infections, which may help justify the implementation of shoot thinning in a given vineyard.  For example, it has been found that higher shoot density may contribute to the increased incidence of Botrytis rot infections in susceptible cultivars such as Seyval Blanc (9) and Vignoles (4).

In other cases, shoot thinning improved fruit composition in Pinot Noir and Cabernet Franc for two consecutive vintages (1), and also increased color intensity, phenolic content, and total anthocyanins of Cabernet Franc berries (1). Benefits of shoot thinning on fruit quality and wine sensory perception have been reported for other vinifera cultivars, such us Barbera (10) and Sauvginon blanc (11).

Unless your vineyard is located in a low or moderate vigor site, shoot thinning is strongly recommended for vinifera cultivars growing in the Mid-Atlantic region.

If you want to assess the effects of shoot thinning on fruit composition, plan to leave half of a row of vines un-thinned and thin the remaining half to a consistent number of shoots per foot (e.g., 4 shoots per foot). Alternatively, use two rows (of the same variety and cultivar) to assess the impact of shoot thinning in your vineyard: one row thinned and the adjacent row un-thinned.  These two methods should help evaluate the effect of shoot thinning on berry composition at harvest and if possible, on wine chemistry and sensory perception assuming that the lots of berries can stay separated through wine production.

Effects of shoot thinning on vine physiology

Impacts of shoot thinning on vine physiology and performance are complex.  A study conducted in Italy evaluated the whole-canopy photosynthetic response to shoot thinning using spur-pruned Barbera vines (V. vinifera; 10). Vines were thinned to 5 shoots per foot, reducing the total shoot number by 50% as compared to un-thinned control.  In this study (10) shoot thinning significantly improved grape sugar content, color, and phenolics. Despite the benefits provided by shoot thinning on fruit composition, which has been already reported by other studies, what makes this study unique and interesting it that they investigated the mechanisms behind the improvement in grape quality through the measurement of whole-canopy net carbon assimilation.  Although the shoot-thinned vines had initially lower photosynthesis (carbon assimilation) than un-thinned vines due to the removal of photosynthetic source (leaf), they had regained photosynthetic capacity to levels similar to the un-thinned vines within 17 days of treatment.  This occurred as a result of a substantial increase in both main leaf size and amount of lateral leaves as a result of shoot thinning (10).  Therefore, individual shoots of thinned-vines had a higher supply of assimilates (e.g., sugar) per unit of crop, which can increase sugar accumulation during ripening. This may explain why shoot thinning improved grape composition in Barbera under these growing conditions.

Additional Shoot Thinning Resources

 

References Cited

  1. Reynolds AG., et al. 2005. Timing of shoot thinning in Vitis vinifera:  impacts on yield and fruit composition variables.  56, 343-356.
  2. Intrieri, C and Poni, S. Integrated evolution of trellis training systems and machines to improve grape and vintage quality of mechanized Italian vineyards.  AJEV.  46, 116-127.
  3. Fiola, J. 2017. Canopy Management – Shoot thinning and positioning. “Timely Vit” from UMD Extension.
  4. Walter-Peterson, H. 2013.  Shoot thinning:  Good for the vines, but good for the wines?  Finger Lakes Vineyard Notes.
  5. Martinson, T and Vanden Heuvel, J. Shoot density and canopy management for hybrids. CCE. http://www.fruit.cornell.edu/grape/pdfs/Canopy%20Management%20for%20Hybrids%20-2007.pdf
  6. Sun Q., et al. 2011. Impact of shoot thinning and harvest date on yield components, fruit composition, and wine quality of Marechal Foch.  AJEV. 62:1, 32-41.
  7. Sun Q., et al. 2012. Impact of shoot and cluster thinning on yield, fruit composition, and wine quality of Corot noir.  AJEV. 63:1, 49-56.
  8. Morris, JR. et al. 2004. Flower cluster and shoot thinning for crop control in French-American hybrid grapes.  AJEV. 55:4, 423-426.
  9. Reynolds, AG et al. 1986. Effect of shoot density and crop control on growth, yield, fruit composition, and wine quality of ‘Seyval blanc’.  J. Amer. Soc. Hort. Sci. 111, 55-63.
  10. Bernizzoni, F. et al. 2011. Shoot thinning effects on seasonal whole-canopy photosynthesis and vine performance in Vitis vinifera L. cv. Barbera. Aus. J. Grape Wine Res. 17, 351-357.
  11. Naor et al. 2002. Shoot and cluster thining influence vegetative growth, fruit yield, and wine quality of ‘Sauvignon blanc’ grapevines.  J. Amer. Soc. Hort. Sci. 127(4), 628-634.

 

Maria Smith is a viticulture PhD candidate with Dr. Michela Centinari in the Department of Plant Science.  She specializes in cold stress physiology of wine grapes.  She was the previous recipient of the John H. and Timothy R. Crouch Program Support Endowment, an endowment founded and funded by the Crouch brothers, original owners of Allegro Winery in Brogue, PA.  She is currently funded by the Northeast Sustainable Agriculture Research and Education (NE-SARE) program, a program from the USDA National Institute of Food and Agriculture (NIFA).

Three Phases to Managing Grape Berry Moth

By: Andy Muza, Penn State Extension – Erie County

As the season begins, growers should be prepared to manage a serious pest which can cause substantial economic losses. The grape berry moth (GBM) is a prevalent pest of grapes throughout Pennsylvania and the eastern United States. The larval stage feeds on berries and causes yield losses due to consumption and shelling of berries and by providing entry sites for fungi that can cause cluster rots.

I consider management of this pest to be a three phase process which includes: 1) PRE –TREATMENT  Phase; 2) TREATMENT  Phase;  3) POST – TREATMENT  Phase.

1) PRE-TREATMENT PHASE

Sprayer Maintenance

Follow maintenance procedures outlined in your sprayer manual. Check pump, hoses, filters, nozzles, etc. to be sure that everything is in good working order before your first pesticide application.  Also practice routine sprayer maintenance during the season such as lubrication of bearings and cleaning and flushing of the sprayer after each use.

Calibration of Sprayer

Sprayers should be calibrated early in the season well before any insecticide or fungicide spraying is required. Calibration of sprayers ensures that the appropriate amount of spray material is being applied where it is needed to manage pests. The sprayer should be calibrated in the vineyard under conditions in which the sprayer will be operated. Ideally, sprayers should be calibrated 2-3 times during the season as canopy growth increases.

Classifying a Vineyard Using the GBM Risk Assessment Program 

The GBM Risk Assessment Program was developed by Hoffman and Dennehy (Cornell University), (“Bulletin 138, Risk Assessment of Grape Berry Moth and Guidelines for Management of the Eastern Grape Leafhopper”  –  http://nysipm.cornell.edu/publications/grapeman/files/risk.pdf).  It is a method of classifying vineyard blocks for risk (e.g., High, Low or Intermediate) of receiving damage from grape berry moth. The criteria used for assigning risk include: Value of the varieties being grown; Surrounding Vineyard Habitat; History of GBM injury; Climatic factors related to the region where grapes are being grown.

High Risk Classification  

Value of the varieties being grown – if higher value varieties such as Vitis vinifera, many hybrids, or table grapes are being grown then these vineyards should automatically be assigned a High Risk Classification. Therefore most vineyards in Pennsylvania, outside of the Lake Erie Region, should initially be classified as High Risk. This classification can be adjusted later if scouting history reveals that GBM injury is consistently low at your vineyard site.

Surrounding Vineyard Habitat – if wooded edges or hedgerows/weedy areas are present around vineyards.

History of GBM injury – if scouting reveals that damage is often above 6% cluster damage in July and /or above 15 % cluster damage (2% berry damage) at harvest. These injury levels were developed with processed juice grape varieties in mind and injury levels may be lower for varieties that command a higher value/ton.

Climatic factors related to the region – if a region has prolonged winter snow cover or mild winter temperatures.

Low Risk Classification

Value of the varieties being grown – if lower value varieties (e.g., juice grapes) are being grown.

Surrounding Vineyard Habitat – if no wooded edges or hedgerows/weedy areas are present around vineyards.

History of GBM injury – if vineyards seldom have problems with GBM. The history of GBM injury for each site is acquired by maintaining scouting records of vineyards over the years.

Climatic factors related to the region – if permanent snow cover is rare and site is prone to severe winter temperatures.

Intermediate Risk Classification – is a catch all classification.  If it isn’t High or Low risk then site is classified as Intermediate risk.

Life cycle and description of GBM

Knowledge about the life cycle and ability to identify the pest and injury caused is important for successful management. Moths emerge from the overwintering pupal stage in spring. Emergence in Erie County, Pa. occurs in late May but in other areas of the state this may occur 2 -3 weeks earlier. These moths are small (about 6 mm), brownish with grey-blue coloration at the base of wings (Figure 1). Unless pheromone traps are used it is unlikely that moths will be observed. Adults are active around dusk and have a distinctive zig zag pattern in flight. Mated females lay eggs singly on flower clusters or berries. Eggs are very small (< 1mm), scale-like and whitish, opaque (Figure 2). Due to their size, eggs are difficult to observe without a hand lens. Early in the season larvae hatching from eggs will web together small berries to feed. However, when berries reach about 5 – 7 mm in size, larvae will bore directly into berries to feed. Newly hatched larvae are tiny with white bodies and black head capsules. Later stages are brownish to purple in coloration (Figure 3). Upon completing development larvae exit berries and either drop to the ground to pupate in leaf litter or some will pupate in the canopy in a semicircular leaf flap. Pupae which are encased in leaf sections are light brown to greenish in coloration (5 mm). Leaves with pupae will remain underneath the trellis if there is poor weed control or will be moved by the wind and collect along wood edges, or in brushy areas. Adults will emerge from pupae to begin the next generation. There are usually 3 – 4 generations of GBM per year in Pennsylvania, depending on temperatures during the growing season.

Figure 1. Grape Berry Moth adult on Concord leaf. Photo by: Andy Muza, Penn State

 

Figure 2. Grape berry moth eggs on Concord cluster. Photo by: Andy Muza, Penn State

 

Figure 3. Grape berry moth mature larva on berry. Photo found at: Grape Berry Moth fact sheet http://nysipm.cornell.edu/factsheets/grapes/pests/gbm/gbm_fig3.asp

Scouting                                                                                                                                                                                           

Regular scouting throughout the season (at least weekly) is critical in determining if and where applications should be applied for GBM.  A scouting protocol for GBM is described in “Bulletin 138, Risk Assessment of Grape Berry Moth and Guidelines for Management of the Eastern Grape Leafhopper” .

This protocol recommends selecting four different areas in your vineyard to be sampled during each scouting event. Two different areas should be checked in the interior of the vineyard and two different areas along the exterior (border) portions of the vineyard. At each of the four sampling sites, randomly select 5 vines and examine 10 clusters/vine for GBM injury. Determine separate injury levels (# injured clusters/100 clusters = % injured clusters) for the interior and exterior portions of the vineyard. It is important to keep separate injury levels for the interior and exterior areas because border areas near woodlines/hedgerows will usually have higher levels of injury. Therefore, border areas may need an insecticide application while interior areas may not.

When scouting early in the season look for webbing in the clusters (Figure 4). Until berries are large enough to enter, larvae will web together multiple berries and feed from inside webbing sites. Some varieties (e.g., Concord) may exhibit a distinct reddening of portions of the berry if injury occurs before veraison (Figure 5) while other varieties do not (Figure 6). Later in the season look for holes, splits, webbing or dark tunneling underneath berry skin (Figure 7).  If injured berries are broken open then larvae may be found.

Figure 4. Webbing in cluster from GBM larva. Photo by: Andy Muza, Penn State

 

Figure 5. Reddening of Concord berries caused by GBM injury. Photo by: Andy Muza, Penn State

 

Figure 6. GBM entry holes in Niagara berries. Photo by: Andy Muza, Penn State

 

Figure 7. Late season GBM injury on Concord berries. Photo by: Andy Muza, Penn State

Map vineyards and keep scouting records – Develop detailed maps of your vineyards and surrounding topography. Keep records of GBM injury levels for each scouting date and vineyard sections checked. These records will provide a GBM history per site.

Pheromone Traps – GBM flight periods can be monitored using commercially available pheromone traps (Figure 8). Traps and pheromone caps can be purchased from a number of sources such as at Great Lakes IPM, Inc.  and  Scentry Biologicals, Inc.  Monitoring traps are baited with small rubber lures impregnated with GBM female sex pheromone for attracting male moths. Pheromone traps may provide an idea of population levels at your vineyard site and can be used as a scouting tool to indicate flight periods. However, trap data are not used for timing of spray applications due to ambiguity concerning correlation of capture numbers and berry injury levels.

Figure 8. Pheromone trap for monitoring GBM flight periods. Photo by: Andy Muza, Penn State

Cultural Practices

Cultural practices are integral for any integrated pest management program. Therefore, maintain good weed control under the trellis. Poor weed management resulting in excessive vegetation under the vines can harbor grape berry moth (GBM) pupae.

Viticultural practices that promote a more open, less dense canopy resulting in better exposure of clusters to sunlight (e.g., shoot thinning, leaf removal, judicious use of nitrogen) will not only improve quality of fruit but will enable better spray coverage.

Vineyard area maintenance such as preventing overgrown, weedy areas around the vineyard will reduce overwintering sites for GBM pupae. If possible, removal of wild grapevines near the vineyard will decrease potential reservoir sites.

2) TREATMENT PHASE

Spray Timing

To accurately time insecticide applications it is recommended that the Grape Berry Moth Degree-Day Model be used. The GBM DD Model is a temperature-driven developmental model developed by Tobin and Saunders at  Penn State. This model is incorporated into Cornell’s Network for Environmental and Weather Applications (NEWA).  Collaborative research at Penn State, Cornell and Michigan State Universities has shown that use of this developmental model can improve GBM management. For a comprehensive explanation concerning the development and use of this forecasting model consult   “Focus on Females Provides New Insights for Grape Berry Moth Management” , Issue 14, May 2013.

Use of the GBM DD Model:

  • CHECK the NEWA weather station closest to your vineyard. There are a number of NEWA weather stations located throughout Pennsylvania.  However, the majority of vineyards outside Erie County, PA will probably not be close enough (i.e., within a few miles) to a NEWA station for this option to be useful. But you can still use the GBM DD Model by recording daily maximum and minimum temperature data on your own. Options include either purchasing a max/min thermometer or weather station for your site. The RainWise AgroMET & IP-100 Package   http://www.rainwise.com/  is the authorized choice for participation into the NEWA network.
  • MONITOR and RECORD the date of wild grape bloom (i.e., when approximately 50% of flowers open) for each vineyard site. Research has shown that egg laying by females that emerge in the spring (first generation) is closely associated with bloom of wild grapevines. Therefore, the majority of eggs from this generation are laid on wild grape clusters and not in cultivated vineyards. NOTE: If using a NEWA site then enter the date of wild grape bloom into the model. If you do not record a wild grape bloom date for your site then the model does provide an estimated date for the weather station that is used.
  • TRACK GBM degree days using a NEWA station closest to your vineyard site OR keep a running total throughout the season of GBM degree days [(Daily MAX + MIN Temperatures)/2) – 47.14 F] starting on the recorded date of wild grape bloom.
  • SCOUT to determine injury levels.
  • SPRAY (if needed) as close to the designated degree day timings as possible.

The model recommends an insecticide treatment in high and possibly intermediate risk sites when: 810 GBM degree days are accumulated for the second generation; 1620 GBM degree days for the third generation; and 2430 GBM degree days (if harvest has not yet occurred) in years that a fourth generation occurs. Insecticides such as Intrepid, Altacor, and Delegate are suggested for these timings.

If using broad spectrum contact insecticides (e.g., pyrethroids) then applications should be delayed about 100 GBM degree days for each generation (i.e., 910, 1720, 2530 GBM degree days).

Insecticide Choices/Application Practices

There are numerous insecticides effective for GBM which are registered for use in Pennsylvania. Consult the 2017 New York and Pennsylvania Pest Management Guidelines for Grapes (https://store.cornell.edu/p-197039-2017-new-york-and-pennsylvania-pest-management-guidelines-for-grapes.aspx).

Rotate insecticides with different modes of action into your GBM spray program to prevent/delay insecticide resistance. Read the label to determine if a spray adjuvant and/or pH adjustment to spray water is required. Also, incorporate more selective insecticides (e.g., Intrepid, Altacor, Delegate) into your spray program which will aid in conserving natural enemies.

Good spray coverage on clusters is critical. Therefore, spray every row and use appropriate gallonage, speed, pressure, and nozzles for good cluster coverage as the size of the canopy increases throughout the season.

3) POST-TREATMENT PHASE

Evaluate efficacy of applications

Don’t assume that because an insecticide was applied that GBM was controlled. After an insecticide application check areas that were sprayed to determine the effectiveness of the application. High Risk sites in Erie County, PA have benefited from back to back applications (about 10 days apart) per generation due to extremely high population levels at these sites.

Continue to Scout                                                                                                                                                                        

Monitoring your vineyard(s) not only for GBM but also for other insects, diseases and weeds should continue through harvest.

Keep Accurate Records

Accurate records should be kept each season for: scouting (e.g., dates, pests observed, vineyard location where observed, injury levels); pesticide applications (e.g., pesticides used, rates/acre, gallons/acre applied, etc.) and weather data.

Re – examine management practices

At the end of the season, especially if GBM was not adequately controlled, re – examine management practices by reviewing your records. A few factors to consider that contribute to poor control include: Inadequate Spray Coverage; Inaccurate Spray Timing; Too Few Applications; and Choice of Insecticides.

Change/Fine Tune management practices

The results of re-examining your practices may reveal flaws in your management strategy. If flaws are identified then be prepared to make the necessary changes in the future. Fine tuning your pest management strategy is an ongoing process which should evolve as long as you continue to farm.

2017 Pre-Bloom Disease Management Review and Discussion

By Bryan Hed

Another season of grape growing is upon us and it’s a good time to review important disease management principles and be aware of some of the tools to consider integrating into your vineyard management programs this spring.

First is your annual reminder to check out the NEWA website (Network for Environment and Weather Applications) found at http://newa.cornell.edu. On the home page is a map of the Northeastern U.S. marked with the locations of hundreds of weather stations where historical and ‘up to the hour’ weather data can be viewed. Although is provided free on the internet, it is funded through the New York State IPM program. Click on a weather station near enough to you (denoted by a leaf/rain drop icon) to get weather, insect pest, and disease information you need to make important management decisions that could save you time and money. Clicking on ‘grapes’ under ‘crop pages’ will give you access to forecasting models for all the major diseases, as well as the grape berry moth degree day model that will improve your timing of grape berry moth insecticide sprays later this summer. Each model forecast is accompanied by helpful disease management messages and explanations.

Next, let’s move our minds into the upcoming pre-bloom disease management season. It’s important to recognize that the threat of disease this spring (pre-bloom) is largely determined by the amount of overwintering inoculum in your blocks. The amount of overwintering inoculum is dependent on the amount of disease that developed in your vineyard last year or in previous years. In other words, if you have kept diseases well under control in the past, especially last year, then there will be relatively little for pathogen populations to build on and cause damage, at least initially, this year. Some very practical research by Wayne Wilcox at Cornell nicely illustrates this point with powdery mildew (pm) development in susceptible wine varieties. In blocks where pm was well controlled all season, fewer overwintering structures of the fungal pathogen (chasmothecia) were available the following spring to jump start disease cycles. Early disease pressure was relatively low and early sprays were less critical to good commercial control than in blocks where disease control was poor the previous year. Where there was poor control the previous year, more of the pathogen overwintered to start disease cycles the following spring and early sprays were critical to maintaining successful commercial control. This is not to say that a bad year of pm will automatically be followed by another bad year. But it certainly tilts the odds in favor of the pathogen, especially if for some reason, you can’t manage the timely application of your early disease control program (stuff happens). It also doesn’t mean you can slack off this year if you had good control last year. Remember, there’s the weather. The weather ALWAYS plays an important role too. A good illustration of this is an experience by an organic grape grower who, in an extremely wet season, developed a serious, economically damaging case of black rot. In conventionally managed vineyards there are several very effective chemistries to control black rot, but in organic production there are no real effective fungicides, and control of this disease in organic vineyards must rely heavily on cultural measures that reduce the pathogen’s overwintering population. Of course, the grower did everything he could to sanitize the trellis of overwintering fruit mummies and bury mummies that had fallen to the ground to reduce overwintering inoculum. But fortunately, the following year was bone dry during the fruit susceptibility period and black rot was not even an issue. Had the previous wet season been followed by another wet one, I’m quite certain, the battle for control of black rot in that organic vineyard would have required ‘the kitchen sink’ to avoid losses. Unfortunately, we have no control over the weather and accurate forecasts, especially long term, are not something to rely on. But, we can (and should) strive to control overwintering inoculum levels every year and the best way to do that is good, practical, season-long disease control.

So, begin to wrap your minds around the campaign ahead. If you had poor disease control in some blocks last season, have you reviewed your spray records where control failed AND where it worked well? Where it failed, did you use the wrong material at a critical time?  I’ve had growers discuss their control failures with me only to discover that their timing was fine, but their choice of material did not cover the disease(s) they intended to control. The number of spray materials, what disease each one controls, and how well each one controls each disease, can be bewildering at times…and the list keeps growing and changing. Also, materials that used to be good choices may have become ineffective due to the development of resistance by the pathogens. For example, materials like the strobilurins (Abound, Sovran, Flint, Pristine) are no longer effective at controlling powdery and downy mildew in many parts of the east. In vineyards where this has occurred, using them during the critical fruit protection period (which used to be a great idea!) can now prove disastrous. The sterol inhibitor fungicides (Rally, Elite, Orius, Mettle, Tebusol, Tebustar, Procure, Viticure, etc) are also exhibiting the effects of resistance by the powdery mildew fungus. Though in most cases they still work on powdery to some extent, they are not appropriate for the critical fruit protection period anymore, around and shortly after bloom (products that include the more active difenoconazole are an exception on less susceptible varieties). However, they may be acceptable for maintaining a clean vineyard outside the critical period. Do you have an accurate grasp on that?

Do you have a firm grasp on the critical fruit protection period? The critical period for fruit protection from all diseases generally extends from ‘just before bloom’ to about 4 weeks later. This is the period when you need to be especially vigilant about minimizing spray intervals, using your best materials that cover all the major diseases (Phomopsis, black rot, powdery and downy mildew), focus on good coverage, etc. It is never profitable to try to cut corners during the critical period. However, if you had heavy amounts of black rot in your vineyard the year before, you should assume you have an unhealthy dose of overwintering inoculum in your vineyard this spring, and prevention of leaf lesions in the fruit zone (which would need to be addressed during the first 3-12” of shoot growth, well before the fruit protection period) would also prove to be critical. This goes for other diseases as well (refer back to the previous example with Wayne Wilcox’ powdery mildew experiment). The pre-bloom presence of visible disease in the fruit zone is a big red flag; it means you’ve got potential for serious fruit loss ahead, especially if weather conditions favor the pathogen (wet, warm, humid, calm, cloudy) during the fruit protection period that follows.

Did you record the relative levels of disease that developed in years past for each of your blocks? In order to do this, you need to be able to identify the various diseases and then scout regularly for them. This takes up valuable time but you can streamline your scouting efforts in many ways. Do you know when you would expect to first see each disease? Downy mildew doesn’t become active until about the 5-6 leaf stage. So, you know you can’t expect to see it until about that time or shortly after that. In which blocks are diseases most likely to occur first? Your block or rows next to the woods would be a good place to start, or perhaps your most susceptible variety. Blocks with the most disease last year would be a good place to start. On which parts of the vine do you expect to see diseases appear first? Can recent weather data help you to determine where to look for the disease? For example, if a black rot infection period occurred 2 weeks ago (and you can find this out easily by searching the NEWA website), would you examine the newest growth, the oldest growth, or would you look for lesions on leaves that were currently expanding and most susceptible 2 weeks ago? The answers to these questions can help you streamline your scouting efforts, save time, and improve your expertise.

Do you fully comprehend the susceptibilities of all the varieties you’re growing? You cannot spray premium Vitis vinifera like the hybrids or natives and expect the same results. What are you going to change this year to address disease control breaches in your vinifera? If you had good control last year, are you ready to do it again this year? OR, do you feel lucky and plan to back off until close to bloom to apply your first spray? I always plan for the worst when it comes to the weather and assume it’s going to be wet, cloudy, and warm; ideal for fungal disease epidemics. Consider that here in the east we are growing a highly vulnerable, susceptible host (wine grapes) on the pathogen’s ‘turf’ (the wet, humid eastern U.S.). The good news is that disease control during the pre-bloom period is generally easier (good spray coverage not a problem, low initial disease/inoculum levels, etc.) and cheaper (can use lower fungicide rates, lower spray gallonage, less expensive materials, less time, etc) than in the post bloom period, and a well prepared pre-bloom disease management program will provide extra insurance against problems during bloom and early fruit set, when your fruit ($) is most vulnerable. Now let’s review the common diseases with some of these questions and concepts in mind.

Phomopsis cane and leaf spot is often the first disease problem we face in the pre-bloom period, particularly where trellis systems maintain lots of old and/or dead wood. That’s because old and/or dead wood is where the pathogen overwinters. Therefore, the more old wood you have in your trellis, the more inoculum you can expect to be battling with this spring. Conversely, cane pruned systems have fewer problems with Phomopsis, and cane pruning/minimizing older wood is an important cultural control for this disease. Fortunately, many areas of PA and other parts of the east experienced a relatively dry spring in 2016, helping to minimize new overwintering infections on year-old wood. But, older cordons and especially dead wood and pruning stubs, can carry overwintering inoculum into many subsequent springs. So, if there was little opportunity for new Phomopsis infections to occur last year, you can still be carrying a fair amount of overwintering inoculum in old cordons and pruning stubs.

During early spring rains, Phomopsis spores flush from lesions on wood and are splashed about to invade any new shoot, leaf, and inflorescence they land on…provided the wetting period/temperature combination falls within a minimum range for infection. The basal-most (oldest) internodes of new shoots are the most susceptible to shoot infections simply because they are closest to the inoculum source; wood. In every trial where I have rated shoot infection of Phomopsis, the most severe lesion development was ALWAYS found (on average) on the first (oldest) internode region of the shoot. Lesion development typically got less severe as my rating progressed through internodes 2, 3, 4, and 5. However, once these internodes become fully expanded after the first few weeks in the season, they are no longer susceptible to lesion development. I rarely see Phomopsis lesion development beyond the fifth internode region. That’s why this disease is best dealt with preventatively, very early, during the first few inches of shoot growth. Infections that occur on the first few internodes of new shoots are not only the most likely to occur, but also the most critical; infections of inflorescences (generally on nodes 2-5) can lead to crop loss early (parts of the inflorescence may be ‘bitten off’ by the pathogen) or later during ripening (cluster stem infections in spring move into berries and cause fruit rot and shelling after veraison). And, infections that occur on the basal-most internodes, can’t all be eliminated by judicious hand pruning during the dormant season. So, in blocks where you suspect any risk of early Phomopsis infections, applications of a fungicide (mancozeb or captan are good choices) at no later than 3-6” of shoot growth are a good investment, particularly if you are not cane pruning. Following up with fungicides at 8-12” shoots and immediate pre-bloom are also important pre-bloom applications. Below are some pics from last year’s blog (Figures 1, 2) to help you get a handle on the appearance of lesions on year-old canes. Unfortunately, determining the presence of Phomopsis on older wood generally involves more than just a visual assessment.

Figure 1. Dark brown lesions on the first few internodes on these Chancellor canes are from Phomopsis infections that occurred during early shoot growth in the previous year (when these were green shoots). The buds present are just ready to burst open with new shoot growth that will be very vulnerable to infection during subsequent rain periods.

Figure 2. Although the 1” shoot stage can be vulnerable to damage from this pathogen, the more critical stage is at 3-6” shoots, when more shoot, leaf, and cluster tissue is exposed and is highly susceptible (below). Note the inflorescence in the upper right picture from which Phomopsis has “bitten off” whole branches, dramatically limiting yield potential for that cluster.

Pre-bloom fungicide applications for Powdery mildew are also prudent during early shoot growth for Vitis vinifera cultivars and highly susceptible hybrids, especially in vineyards where control of this disease may have slipped last year (again, because of lots of overwintering inoculum). The primary inoculum for this pathogen generally comes from overwintering structures of the fungus that are lodged within cracks in the bark of cordons and trunks. Spring rain periods of at least 0.1” of precipitation and temperatures of 50 F or more, are the requirements for release of primary inoculum (ascospores) from the overwintering structures. The more mildew that was allowed to develop the year before, the larger the release of spores in early spring, the more primary infections that are likely to occur, and the more critical the need to control the disease early. Sulfur, oils, monopotassium phosphate, and potassium bicarbonate materials can be good choices for mildew management early on. All of these materials can eradicate small existing powdery mildew infections on leaves and cluster stems. Most do not generally offer any protection from future infections and therefore work best if applied often. Sulfur is an exception, and has the added benefit of providing a week or more of protection against future infections. Many of the more experienced growers like to utilize a mancozeb/sulfur combination to control all diseases during the pre-bloom period. This combination is relatively inexpensive, there are no resistance issues, and it works. Remember to read labels and be aware that you can’t mix sulfur and oils, or oils and captan. The tebuconazole products can be used during early pre-bloom to control powdery mildew as well, especially at the 8-10” shoot stage. These materials are very inexpensive and generally provide enough powdery mildew control to keep vines healthy until the immediate pre-bloom spray (they will also nicely control early black rot infections). At immediate pre-bloom and first post bloom, you want to apply your best powdery mildew chemistries like quinoxyfen (Quintec), difenoconazole (Revus Top), metrafenone (Vivando), fluopyram/tebuconazol (Luna Experience), etc. For native juice grapes, powdery mildew is rarely a concern during the early shoot growth stages, especially in the cooler Lake Erie region of Pennsylvania.

A note about fungicide resistance management and powdery mildew: It’s important to plan your powdery mildew management choices ahead of time with resistance management in mind. The easiest way to do this is to become familiar with FRAC (fungicide resistance action committee) codes listed prominently on the first page of fungicide labels. Fungicides with the same FRAC group number can be considered similar enough in their mode of action/chemistry that resistance to one is resistance to all others within that group. Therefore when you rotate fungicides for resistance management, you’re essentially rotating FRAC groups. Some good rules to remember are to avoid using the same FRAC group consecutively, or more than twice in a given season. The development of powdery mildew resistance is always a concern when using materials like the strobilurins (FRAC 11), the sterol inhibitors (FRAC 3), Quintec (FRAC 13), Vivando (FRAC U8), Luna Experience (FRAC 7, 3), Torino (FRAC U6), and Endura (FRAC 7) to name a few. Resistance is generally not a concern for uses of sulfur, oils, bicarbonates, and the potassium salts (mentioned above), or copper.

Next, black rot: One of the best ways to reduce overwintering inoculum of black rot is to scout your vineyard for old fruit mummies and eliminate them from the trellis. Black rot infected fruit mummies that have overwintered in the trellis are the most potent source of inoculum for infections the following spring. No matter how cold it gets over the winter, the pathogen survives just beautifully in colonized fruit remaining in the trellis. But, dropping this inoculum source to the soil, allows microbial degradation/weathering to reduce the potential for mummies to release spores the following spring. It also places the inoculum source much farther from new, susceptible plant tissue up in the trellis. The best time to ‘sanitize’ the trellis is during dormant pruning; weathering has already accomplished some of the removal of last season’s infected fruit from the trellis, and what remains is relatively easy to see and remove by hand. Experiments we conducted several years ago clearly showed that the earlier the mummies are knocked to the ground during the dormant period, the more time for decomposition to break them down before the next season, and the fewer spores released from the ground the following spring to start new disease cycles. Nevertheless, some inoculum on the ground will survive to release spores in spring, and burial of mummies with cultivation will go a step further to eliminate the threat. Removal of ALL old cluster material from the trellis before bud break is important to maintaining good control of this disease.

It may not be necessary to apply a fungicide for black rot at early shoot stages IF good control of this disease was achieved the previous year AND conscientious scouting and trellis sanitation has been implemented. However, the importance of early shoot infections should not be underestimated as I mentioned above, especially if they result in leaf lesions in the fruit zone. For example, inoculations we performed from early May to early June (simulating wet weather and an overwintering inoculum source (mummies) in the trellis) resulted in leaf and shoot lesions in the cluster zone (Figure 3). Those lesions went on to release spores during the critical fruit protection period, resulting in crop loss of 47-77% on those shoots with infected leaves!

An application of mancozeb, ziram, or captan for Phomopsis will also provide control of early black rot infections. The sterol inhibitor fungicides and strobilurins are also good materials for black rot that are more rainfast than mancozeb, ziram, and captan. The sterol inhibitors also provide excellent post infection activity that can be very useful at terminating an infection that has already occurred (but not yet manifested itself).

Figure 3. Early (pre-bloom) black rot leaf infections in the cluster zone provide inoculum that can add to problems with controlling fruit infection after capfall. The two small tan lesions on the leaf at node 2 are just inches from the developing inflorescence found at node 3 (picture on the right). These lesions will release spores during rainfall periods that could easily be splashed to highly susceptible cluster stems pre-bloom, and developing fruit after capfall. Resulting fruit infections will lead to crop loss.

Downy mildew and the 5-6 leaf stage: This stage marks the point at which the downy mildew pathogen first becomes active and is capable of releasing primary spores from inoculum sources that have overwintered on the ground (leaves and other plant material that was infected during the previous season). As with all other diseases, vineyards that developed a fair amount of downy mildew leaf/cluster infection last year will be at higher risk this spring than vineyards that were kept clean. However, overwintering structures of the downy mildew pathogen can survive more than one season in the soil.

Periods of rainfall with temperatures of at least 52 F meet the requirements of spore release and the first infections; plant surfaces must be wet for infection to occur. While scouting for this disease, expect to see it first in wetter areas of your acreage and pay close attention to leaves near the ground (sucker growth, grape seedlings that germinated from shelled berries last fall) which are most likely to become infected first. Therefore, keeping such low growth to a minimum in spring is a prudent control measure that can delay the development of the disease. It also suggests that if you’re planning vine trunk renewal from sucker growth, you will need to apply fungicides to protect that growth from the ground up as the pathogen becomes active.

Spring leaf infections are identified by the yellow ‘oil-spots’ seen on the tops of leaves (Figure 4), coinciding with white, downy sporulation of the pathogen on the undersides of leaves. Inflorescences can be blighted and show sporulation as well. Sporulation occurs during darkness under high relative humidity, and can typically be seen during a morning scout of the vineyard following a wet/humid night. Under optimum temperatures (70-75F), only an hour or two of plant surface wetness may be required for infection to occur, and new infections can produce their own spores with just 5 days.

Many parts of the northeast experienced drought conditions last year, which severely inhibited the development of this disease. Up in Erie County PA, the disease basically took a vacation in 2016, and I could barely find a handful of lesions on unsprayed ‘Chancellor’ leaves and fruit near the ground all summer: it was the perfect year to start renewal trunks! It wasn’t until later in August that rains finally returned and we began to see a few more infections, but for the most part the disease literally could not get off the ground in Erie county PA in 2016. What does this mean for 2017? The great lack of downy mildew in drought hit areas last year means that pre-bloom disease cycles this year will have to rely on overwintering inoculum from previous years (although spores of downy mildew can travel long distances between vineyards, the first infections will arise from inoculum within your vineyard). I have not found any detailed information as to how long the pathogen can survive in the soil, but I guarantee that if you’ve had downy mildew before, then it’s still there. Whether your area was wet or dry last spring, the principle described earlier still applies: vineyards devoid of downy mildew last year (whether from drought or just plain good control) will be easier to keep ‘clean’ in the pre-bloom period this year.

Mancozeb products are good options for the first downy mildew, Phomopsis, and black rot sprays in the pre-bloom period. Ziram and Captan have a similar spectrum of control, but Ziram is a little weaker on downy mildew, and Captan a little weak on black rot.  However, these may be a viable option if these diseases are not a huge threat early on (that is if you had good control last year). These materials are all surface protectants subject to wash-off by rainfall, which means that under heavy, frequent rainfall conditions, application intervals will need to be minimized (7-10 days?) especially for highly susceptible varieties. For that more critical ‘immediate pre-bloom’ spray (and the first post bloom spray), there are other materials like Presidio, Revus, Revus Top, and Zampro that are quite rainfast, very effective, and will provide longer range protection under wet conditions (when you need the protection most and are least likely to be able to stick to shorter spray intervals). However, products like Presidio also require a second active ingredient (like mancozeb) in a tank mix for resistance management purposes (which isn’t a bad idea at this critical spray timing in any case). Other materials like the phosphonates, Ranman, and the strobies /Reason, are probably best utilized outside the critical two sprays around bloom (especially for V. vinifera and highly susceptible hybrids), unless they’re used as tank mix partners with other effective materials. They’re very good materials, but they’re just not the ‘best of the best’.

Figure 4. Yellow oil-spot symptoms of downy mildew on young spring leaves.

One more time for emphasis: the immediate pre bloom and first post bloom (7-14 days later) fungicide applications are the most important you’ll make all year, regardless of variety grown and disease pressure. These two sprays protect your fruit from all the major fungal diseases (Phomopsis, black rot, downy and powdery mildew). Make sure sprayers are properly calibrated and adjusted for best coverage on a bloom-period canopy, spray every row at full rates and shortest intervals, and NEVER extend the interval between these sprays beyond 14 days.

‘Newer’ Fungicides: Aprovia (solatenol) may be worth a try for powdery mildew control (received federal registration in 2015). The active ingredient is related (same FRAC group) to Boscalid (found in Endura and Pristine) and Fluopyram (found in Luna Experience). It also has activity against black rot, but should not be expected to control this disease under high pressure on a susceptible variety.

***Lastly, to help you with all your grape management decisions this year, you should have…

New York and Pennsylvania Pest Management Guidelines for Grapes. An inexpensive, excellent source of research based information for commercial growers; some information in this blog was gleaned from it and it is revised every year to include the newest information. Copies can be purchased at the Cornell Store at https://store.cornell.edu/c-875-pmep-guidelines.aspx. It sells for about $31.

 

Will The Brown Marmorated Stink Bug Be A Problem In Wine And Juice?

By: Jody Timer, Research Technologist

The brown marmorated stink bug (BMSB), Halyomorpha halys (Stal) is an invasive species that has become a major pest in the eastern United States. This pest originally became a sizable problem in Mid-Atlantic vineyards, including southwestern Pennsylvania, during the 2010 growing season and continues to be a large-scale problem. The Lake Erie grape belt is the largest Concord grape growing region in the world. The recent appearance of the brown marmorated stink bug in Lake Erie vineyards has the potential to become problematic. After the mild winter of 2015-2016, the numbers of BMSB in this area began to increase rapidly. This winter, frequent complaints have been received from homeowner concerning the presence of BMSB in their houses.

BMSB have been found in both grape foliage and grape clusters; they seek the moisture, sugar, and warmth on the inside the clusters (especially overnight) and they often migrate to the cluster’s interior close to harvest. This makes the possibility of BMSB inside the cluster very likely when these grapes are mechanically harvested and transported to the processor.

Brown Marmorated Stink Bug in a Grape Cluster

All BMSB life stages (5 instars) have been observed in vineyards indicating that grapes are a suitable crop for BMSB development, and all stages have been found to cause direct damage to grapes (Bernon 2004). At the Lake Erie Grape Laboratory, we have maintained an adult BMSB colony on a diet of Concord grapes with no apparent development problems. It has also been estimated that the presence of 5 BMSB per grape cluster may lead to 37% loss in grape yield as a result of BMSB damage (Smith et al. 2014). With the yearly increase of numbers of BMSB in the Pennsylvania vineyards, the possibility of BMSB tainting the juice produced in this area is becoming a primary concern to processors, growers, marketers, and consumers.

Life stags of the Brown Marmorated Stink Bug. Photo from: http://www.mda.state.mn.us/plants/insects/stinkbug.aspx

Insects produce small, volatile molecules that may be imparted to juice and wine during crush. Humans are able to detect these molecules at extremely low concentrations. For example, 2-isopropyl-3-methoxypyrazine (IPMP) from Multicolored ladybeetles (ladybug taint) is detectable at 0.30 ng/L concentrations in Concord grape juice (Pickering et al. 2008). BMSB have a distinctive odor which has been described as green, cilantro-like, which may or may not be off-putting within grape juice aroma. BMSBs produce taint associated compounds as allomones, alarm pheromones, aggregation pheromones, and kairomones. These compounds are mainly released from the dorsal abdominal glands in nymphs and paired metathoracic glands in adults (Baldwin et al. 2014). When BMSBs are crushed along with grape clusters, release of these compounds could potentially taint in the juice.

Multidimensional gas chromatography mass spectrometry (MDGC-MS) analysis of stressed BMSB, adults and nymphs, has been used to identify more than 39 compounds. The volatile compounds in the taint are tridecane, dodecane, trans-2-decenal and trans-2-undecen-1-ol. Tridecane and trans-2-decenal together constitute at least 70% of BMSB taint (Baldwin et al. 2014; Solomon 2013). Trans-2-decenal, is the major irritant and is believed to be responsible for the potent stink odor from BMSB. However, being an extremely unstable compound it can easily break down, and its degradation products lack the distinctive BMSB odor (Baldwin et al. 2014). When trans-2-decenal was added to red wine (Pinot Noir) the morning of testing, the detection threshold was in the low microgram per liter (ug/L) range (Mohekar et al 2015). However, because trans-2-decenal is unstable, this may not reflect what happens when juice is processed and stored. Joe Fiola from University of Maryland, reported that while 5-10 BMSB per 25 pound lug of white grapes imparted a perceptible taint in raw juice for up to four months in some cases, the taint was not perceptible in the wine after fermentation (Fiola 2011).  Mohekar and colleagues, from Oregon State, reported that trans-2-decenal, has a detection threshold in the ug/L range in Pinot Noir wines, and was able to be detected by tasters (Mohekar et al 2016).

Informal sensory testing with the on-site staff was performed at the Lake Erie Regional Grape Research laboratory. Small batches of grape juice were produced using a residential Kitchen Aid® juicer, and increasing numbers of BMSB were added. Batches of juice containing the equivalent of 0, 2, 10, and 25 BMSB per lug (~35 lbs. of Concord grapes) were tasted raw and after high-temperature, short-time pasteurization (HTST) by five staff members. In blinded triangle tests (2 blanks and 1 spiked sample), 5 of 5 individuals correctly identify the spiked sample of the 25 BMSB/lug juice (both raw and pasteurized); for the 10 BMSB sample, 4 of 5 correctly identified the spike in raw juice, and 5 of 5 identified the spiked sample for the pasteurized juice. The following month the pasteurized juice was re-tasted by 10 individuals and similar results were obtained.  These tests suggest 25 BMSB/lug are sufficient to induce a perceivable flavor change in Concord grape juice. Following this testing, a set of samples were processed at the Food Science laboratory of Penn State, using industrially relevant methods (equivalent to Welch’s Corporation processing techniques), to assess if the odor-causing compounds secreted by BMSB were stable enough to transfer through the juicing, processing, pasteurization, and storing of grape juice and therefore cause it to be rejected by consumers. Large scale sensory tests were then run with regular grape juice consumers to quantify rejection thresholds for BMSB-spiked, processed grape juice.

Grape clusters, with varying amounts of BMSB (0, 4, 8, 16, 24, and 32 BMSB, per 35 lbs), were crushed and destemmed; the juice was pasteurized, clarified and blended. Following storage for 8 weeks (2 months after initial processing), sensory testing was performed with grape juice consumers in the controlled sensory testing facility to determine rejection thresholds for different levels of BMSB. Sensory testing was then repeated 8 weeks later (4 months after initial processing).

Despite the use of BMSB levels that clearly caused a noticeable change in the flavor of processed juice in pilot testing, we were unable to find a level of BMSB that caused rejection in consumers following processing and storage at either time point.

As the area’s BMSB population increases, this research will be notably important for processor to determine threshold levels at harvest. This research suggest that taint from BMSB at high but realistic doses for the Lake Erie grape-growing region will not influence consumer acceptability. Conversely however, our results may not generalize to smaller producers in the area who make grape juice using exclusively from Concord grapes. Typically, this juice is sold as fresh juice with a limited shelf life. These smaller growers and producers should be aware of the possibility of taint in their juice especially with the increasing numbers of BMSB in the region. Pre-harvest scouting for BMSB should be conducted to determine if a pre-harvest BMSB insecticide spray should be applied.

https://youtu.be/VzIpLHatLHc

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Bernon, G. (2004) Biology of Halyomorpha halys, the brown marmorated stink bug (BMSB) Final Report—USDA APHIS CPHST Project T3P01. USDA APHIS.

Fiola, J.A. (2011) Brown Marmorated Stink Bug (BMSB) Part 3-Fruit Damage and Juice/Wine Taint. Timely Viticulture. University of Maryland extension,

http://www.grapesand fruit.umd.edu. Accessed October, 2016

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