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.
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.
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).
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.
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.
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.
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.
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.
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.
By: Dr. Michela Centinari
In cool climate vineyards labor (hours/acre) employed for canopy management operations (e.g., shoot positioning and thinning, cluster thinning, leaf removal, hedging) is estimated to be much higher than for floor management practices (approximately 32% vs. 11% of total labor hours, excluding harvest) . Canopy management practices are critical for optimizing crop load, improving microclimate conditions in the fruiting zone and reducing disease pressure on the leaves and fruit. However, we tend to forget that floor management also has profound implications for the vineyard ecosystem, productivity and indirectly wine quality . The main goals of vineyard floor management span from weed control, soil conservation, soil nutrient and water management, and biodiversity improvement . Among many factors, the best floor management strategy for a given vineyard site depends on the age of the vine, growing region, soil type, and production goals of the grower . Environmental regulations and public perceptions may also influence growers’ choices toward a specific floor management practice .
The conventional floor management practice for mature vineyards in the eastern U.S. and other temperate regions around the world is a cover cropped inter-row combined with a vegetation-free area directly beneath the vines to reduce competition for soil resources (i.e., water and nutrients). The under-trellis area is kept bare using herbicides and in some cases by soil cultivation (Figure 1).
Why explore alternative under-trellis management options?
- Seeking environmentally responsible and (potentially) affordable alternatives to the use of herbicides
Herbicides are the most widely used pesticides in the U.S.; they are commonly used in vineyards because they effectively suppress weed growth and are easy to apply . However, repeated herbicide use increases the risks of resistance development . Also, bare soil left exposed after herbicide use or tilling is susceptible to erosion, soil structure degradation and crusting as well as increased water runoff and leaching of nitrates and pesticides .
- Reducing excessive vine growth and the need for expensive canopy management practices
Despite the presence of cover crops between the rows (inter-row area), grapevines can still exhibit excessive vegetative growth in regions with deep,fertile soils and ample precipitation during the growing season (Figure 2). Large and dense canopies with heavily shaded fruit may contribute to reduced fruit and wine quality as well as an increase in disease pressure . In addition, excessively vigorous grapevines are more expensive to train and manage: main and later shoot thinning, multiple passes of fruit-zone leaf removal and hedging are costly management practices  often required to improve clusters light environment.
What are the alternative under-trellis options?
One alternative option to the under-trellis herbicide-treated strip is to establish cover crops directly beneath the vines (intra-row) in addition to between the rows (inter-row) (i.e., complete floor cover) (Figure 3). Under-trellis cover crops could serve multiple purposes depending on grower’s needs and the cover crops species used. Cover crops species have different degrees of competition with vines for soil resources (e.g., water and nutrients). For example, annual cover crops tend to be less competitive for soil nitrogen resources than perennial plants because of their shorter growth cycle and less root development . Furthermore, fine fescues (e.g., Festuca ovina) tend to be less competitive than other perennial grasses such as tall fescues (Festuca arundinacea Shreb) .
Several studies have been conducted in the eastern U.S. over the last 10 years to test if and which under-trellis cover crops species could be used as an environmentally responsible means to suppress the use of herbicide and as a proactive measure to reduce excessive vine grow through competition with the grapevine root system for soil resources.
Do under-trellis management strategies impact leaching of nutrients and pesticide?
Yes, under-trellis management strategies can impact leachate composition [4;9]. For example dissolved organic carbon (DOC) leaching was reduced by maintaining a green cover under the trellis (white clover or native vegetation) as compared to conventional under-trellis strategies, as herbicide (glyphosate) application or soil cultivation . Thus, not only herbicide application but also soil cultivation can increase carbon loss from the soil in addition to increasing its erosivity. Also, total nitrogen (N) concentration was higher in leachate samples collected from under-trellis glyphosate and white clover plots as compared to those from native vegetation or cultivation plots.
What cover crops can growers use to suppress excessive vine growth and increase crop load?
Cool season perennial grasses have been planted under the trellis in vineyard located in Virginia, North Carolina (Dr. Tony Wolf lab, Virginia Tech University) and in Long Island (NY) (Alice Wise, Cornell Cooperative Extension) to impose competition for moisture and nutrients early during the growing season, when grapevines grow vigorously (at least in the Eastern U.S.) [8;9;10].
Compared to an herbicide-treated soil strip, complete vineyard floor cover cropping reduced excessive vigor of Cabernet Sauvignon vines in a wet and humid region (NC) over a six-year-period . Among the perennial grasses tested Festuca arundinacea cv. Elite II, a turf-type tall fescue, and cv. KY-31, a forage-type tall fescue, were the most effective in reducing vine vigor and increasing light available to the fruit with minimum impact on crop yield .
Creeping red fescue (Festuca rubra) planted under Cabernet Sauvignon vines in the fall of the second year of vineyard establishment reduced vine size in a favorable way (average of 26%) and increased sunlight fruit exposure by 35% over a 7-year-period as compared to herbicide-treated strip .
(Note: This study was conducted at the Virginia Tech’s AHS, Jr. Agricultural Research and Extension Center, in a ‘research’ vineyard with high vigor potential. We don’t suggest using under-vine cover crop in young vineyards without knowing the history and vigor potential of the site.)
Interestingly, the growth suppressive effect of the under-trellis fescue decreases over the years suggesting that the vines may be able to adapt to the presence of under-trellis cover crops by, for example, relocating absorptive roots to a deeper soil profile .
Chicory (Chicorium intybus) annually planted under the trellis of mature, vigorous vineyards in the Finger Lakes region of NY resulted in considerably diminished vine size, up to 35 % (Figure 3) [Dr. Justine Vanden Heuvel lab, Cornell University; 12; 13]. Furthermore, chicory effectively suppressed weed pressure underneath the grapevine canopy.
When vine growth is vigorous, the balance between vegetative and reproductive growth tend to be below the recommended Ravaz index (yield /pruning weight) ratio ranging from 4 to 10 for high-quality wine production . The devigorating effect of the under-trellis cover crops often translated to an increase in crop load (i.e., Ravaz index) toward the ‘optimal’ values. Although the reduction in vegetative growth/vine size is usually greater than that of crop yield, growers should take into consideration a potential yield penalty associated with the use of under-trellis cover crops .
Can under-trellis cover crops impact fruit composition?
In several studies the use of under-trellis cover crops did not significantly impact, either positively or negatively, juice chemistry [total soluble sugar (°Brix), pH, titratable acidity (TA)] [4;9;15;16;17] or total phenolics or anthocyanins . In other cases an increase in juice °Brix or reduction in TA (1 g/L) was attributed to the devigorating effect and increased fruit sunlight exposure brought on by the presence of under-trellis cover crops [ 10;12].
What causes the reduction in vine size associated with the use of under-trellis cover crops?
It depends on, among other factors, the seasonal weather conditions, soil resources available and nutritional requirements of the cover crop. Vines can also compete with cover crops for multiple resources at the same time making it in some situations very difficult to separate the effect of moisture vs nutrient competition. In most of the studies conducted in upstate NY, NC and VA vine water status (stem, pre-dawn water potential) never reached what we define a ‘stressful’ value indicating that under-trellis cover crops were not overly competitive with grapevines for soil moisture under the specific weather conditions of those regions and during the years studied [4;10;12;13]. However, during consecutive seasons of summer drought in Long Island, vines with under vine green growth exhibited more symptoms of water stress than those with an herbicide-treated strip 
At several sites, cool-season grasses depressed grapevine nitrogen [4, 10; 12] levels relative to the under-trellis herbicide strip suggesting that under-trellis cover crops can affect vine nitrogen status and thus vine capacity .
What about leaving native vegetation growing under the trellis instead of planting cover crops?
At several research sites in upstate NY, native vegetation was allowed to grow under the vines (Dr. Vanden Heuvel lab, Cornell University). Compared to an herbicide-treated strip, native vegetation had a variable impact on vine size across sites, from nil effect at one site  up to 57% reduction in pruning weight in a young vineyard . Site characteristics, plant material and age in addition to diverse weed populations at the research sites may explain the variable impact of native vegetation on reducing vine size.
Growers in Long Island (NY) have been experimenting with under-trellis mowing (i.e., native vegetation mowed several times throughout the season). Costs of under-trellis mowing compare well to the herbicide regime (approximately $120/acre) . A. Wise pointed out that, while more growers are interested in under-trellis mowing, a deterrent for its adoption may be “the price of suitable mowers, which go from $3,500 for a single head to over $15,000 for two mowing heads with a row middle mower” (Figure 5). Wise also noted that “under vine mowing is a viable option for under vine management though it is best suited to mature, laser planted vineyards because of the risk of trunk damage to young vines and crooked trunks”.
Can under-trellis cover crops be used to eliminate the use of herbicide while maintaining vine size?
Planting annual cover crops, such buckwheat (Fagopyrum esculentum) or annual ryegrass (Lolium multiflorum) under the vines may eliminate the need for herbicide with little impact on vine size or fruit composition. Most of the work on under-trellis annual cover crops has been conducted in the cool and humid Finger Lakes region, upstate NY, at Cornel University by Dr. Vanden Heuvel lab [4; 15; 16; 17]. In the Northeastern U.S. perennial cover crop species are not suitable for the under-trellis area due to the need to mound soil from the under-vine row around the graft union for insulation to protect scion budwood from low winter temperature. For example, buckwheat planted in late-May in in mature vineyards in upstate NY (seeding rate is approximately equal to 350 lbs/acre) was found to compete extremely well with weeds pressure without compromising vine size [13; 16] or fruit composition  (Figure 6).
How much will establishing and maintaining under trellis cover crops cost?
A partial budget analysis was developed for one of the studies on under-trellis cover crops using information gained from the research trial and grower cost estimates (Table 1). In this study establishing and maintaining white clover or native vegetation was a cheaper under-trellis groundcover options than repeated soil cultivation or glyphosate applications. However, vines maintained with herbicide (glyphosate) generated the highest revenue because of their higher yield. Thus, yield penalty associated with vines growing with under-trellis cover crops was the cause of reduced grower’s income. Outcomes could definitely change if crop yield is maintained or only slightly reduced, or if other cover crops are used. Compared to white clover (seeding rate: 5 lbs/acre), creeping red fescue can be more expensive to establish because of its higher seeding rates, as much as 220 lbs/acre . However, fescue can persist for more than four years, while white clover would need to be reseeded every 2-3 years .These figures should be used only as an example because there are many variables that could change the outcomes and growers interested in experimenting with under-trellis cover crops should develop their own cost analysis . Also, vigor suppression associated with under-trellis cover crops may result in reduction of costly canopy management operations.
For grape growers managing vigorous vineyards and interested in reducing pesticide input, complete vineyard floor cover could be a viable option. However, to avoid an undesirable decline in pruning weight, vine nutrient deficiency or water stress it is recommended to monitor pruning weight and Ravaz index on sentinel vines. It is also important to annually assess vine nutrient status and be prepared to efficiently apply fertilizer if needed. In a dry season growers should look closely for visual symptoms of vine water stress. To avoid over-devigorating the vines it may be possible to start with an ‘aggressive’ cover crop and switch after a few years, when vine balance is achieved, to a less competitive cover crops species.
- Yeh AD, Gomez MI, White GB. 2014. Cost of Establishment and production of vinifera grapes in the Finger Lakes region of New York-2013. Cornell University Department of Applied Economics, 716 Ithaca, NY. 717.
- Guerra B, Steenwerth K. 2012. Influence of floor management technique on grapevine growth, disease pressure, and juice and wine composition: a review. Am J Enol Vitic 63:149–
- Skinkis P. Overview of Vineyard Floor Management. eXtension.org.
- Karl A. 2015. Impact of under-vine management in a Finger Lakes Cabernet Franc vineyard. MS thesis, Cornell University, Ithaca, NY.
- Holt JS. 1992. History of the identification of herbicide-resistant weeds. Weed Technol. 6:615–620.
- Landry D, Dousset S, Andreux F. 2006. Leaching of oryzalin and diuron thorugh undisturbed vineyard soil columns under outdoor conditions. Chemosphere 62:1736–1747.
- Austin CG, Grove GG, Meyers JM, Wilcox WF. 2011. Powdery mildew severity as a function of canopy density: associated impacts on sunlight penetration and spray coverage. Am J Enol Vitic 62: 23–31.
- Giese G, Velasco-Cruz C, Roberts L, Heitman J, Wolf TK. 2014. Complete vineyard floor cover crops favorably limit grapevine vegetative growth. Scientia Hortic. 170:256-266.
- Wise A. 2015. Innovative undertrellis management for vineyards. Available at: http://mysare.sare.org/sare_project/lne12-322/?page=final.
- Hickey CC, Hatch TA, Stallings J, Wolf TK. 2016 Under-Trellis Cover Crop and Rootstock Alter Growth, Components of Yield, and Fruit Composition of Cabernet Sauvignon. Am J Enol Vitic. doi: 10.5344/ajev.2016.15079.
- Klodd AE, Eissenstat DM, Wolf TK, Centinari M. 2016. Coping with cover crop competition in mature grapevines. Plant and Soil 4:391–400.
- Jordan LM. 2014. Evaluating the effects of using annually established under-vine cover crops in northeastern Riesling vineyards. MS Thesis, Cornell Univ., Ithaca, NY.
- Karl A, Jordan L, Vanden Heuvel JE. 2015. Investigating annual under-vine cover crops as an enviromentally sustainable alternative to herbicides in northeastern vineyards. SARE Final report.
- Kliewer WM, Dokoozlian NK. 2005. Leaf area/crop weight ratios of grapevines: Influence on fruit composition and wine quality. Amer. J. Enol. Vitic. 56:170–181.
- Centinari M, Vanden Heuvel JE, Goebel M, Smith MS, Bauerle TL. 2016. Root-zone management practices impact above and belowground growth in cabernet franc grapevines. Aust J Grape Wine Res. 1: 137–
- Jordan LM, Björkman T, Vanden Heuvel 2016. Annual under-vine cover crops did not impact vine growth or fruit composition of mature cool-climate ‘Riesling’ grapevines. HortTech 26: 36–45.
- Karl A, Merwin IA, Brown MG, Hervieux RA, Vanden Heuvel JE. 2016. Impact of undervine management on vine growth, yield, fruit composition, and wine sensory analyses of Cabernet franc. Am J Enol Vitic. doi: 10.5344/ajev.2016.1506.
By: Lee Stivers, Penn State Extension Educator – Washington County
June 2015 is certainly shaping up to be one of the rainiest on record for many parts of Pennsylvania. During growing seasons like this, when it seems that every day brings another shower or thunderstorm, most Pennsylvania crop producers start to think about applying supplemental nitrogen to their field, forage and vegetable crops. But what about grapes—should wine grape growers be concerned about nitrogen losses in a rainy year?
Nitrogen is a critically important nutrient for any plant to grow and thrive. However, managing nitrogen in the vineyard can be tricky because vine growth and fruit quality are affected when nitrogen is available in excess amounts as well as when it is deficient. Too much nitrogen can stimulate excessive vegetative growth, throwing the vines out of balance. This is especially true under rainy, wet conditions. That extra vine growth may need to be pruned out later in the season in order to get sufficient air and light penetration into the canopy for proper fruit ripening. Yields can also suffer from excessive nitrogen uptake.
We don’t want to provide too much nitrogen to wine grapes, nor do we want to provide too little. Insufficient nitrogen can reduce crop yield through a reduction in clusters, berries, or berry set. Nitrogen deficiency in wine grapes is not easily recognized, but a typical symptom is a uniform light green color of leaves, compared to the dark green of healthy grape leaves. Typically, soil organic matter decomposition supplies much of the nitrogen needed by grape vines. Nitrogen depletion will occur most rapidly in soils with low organic matter. If soils are not supplying enough nitrogen, then a supplemental fertilizer application may be needed. Soils with adequate organic matter will not necessarily lose much nitrogen during a rainy growing season since organic matter is not soluble.
How do you know if your vines need supplemental nitrogen fertilizer? There is no simple answer to this question, but Tony Wolf provides a very useful set of observations and measurements for assessing the nitrogen status of a vineyard in the “Wine Grape Production Guide for Eastern North America” (page 159-160). By making observations over time of canopy fill, leaf size and color, shoot growth rates and fruit quality, and also measuring yields, cane pruning weights, and bloom-time petiole nitrogen concentrations, you can determine if your vines have a nitrogen status of deficient, adequate, or excessive. In addition to these factors, it is also important to test your soil periodically to monitor soil organic matter levels, as well as other plant nutrients.
How to collect and submit a petiole sample for plant tissue analysis. It’s easy to collect and submit a petiole (leaf stem) sample to Penn State’s Agricultural Analytical Services Laboratory, and you don’t even have to visit an Extension office to purchase a kit. Full instructions can be found here: Penn State Plant Tissue Analysis Submission Instructions and you can download the proper form here: Penn State Plant Tissue Analysis Submission Form.
For routine analyses, petiole samples must be taken at bloom, or at veraison, at least 70 days after full bloom, as these are the only times of year when nutrient levels in the plant are relatively stable. If samples taken at other times of the year are submitted, faulty interpretations could result due to incorrect sampling technique.
To collect the sample, remove 50 to 75 first fully-expanded leaves. Use the higher leaf number for varieties which have small petioles. Samples should be taken from fruiting shoots located halfway between the ground and highest trellis wire. After removing leaves from vines, separate petioles from leaf blades. Send only petioles (leaf stems) for analysis. Loosely wrap the petioles in a dry paper towel. Fill out the form completely, and attach a check, payable to Penn State University, and mail to Penn State Agricultural Analytical Services Laboratory, Tower Road, University Park, PA 16802.
How to take a soil sample and submit it for nutrient analysis and recommendations. Penn State’s Analytical Laboratory also offers soil testing services for commercial growers. This important soil management tool aids in monitoring soil fertility and determining optimum lime and fertilizer requirements for all types of crops, including wine grapes. Full instructions can be found here: Penn State Soil Analysis Instructions and you can download the proper form here: Penn State Soil Analysis Submission Form.
To collect the sample, you will need a trowel, shovel or auger, and a clean bucket. Obtain thin slices or borings from 13-15 randomly selected places in the vineyard. Sample to approximately 12 inches in depth. Collect the samples in the bucket, and mix thoroughly into one composite sample. Spread the soil on newspaper in a warm room to air dry overnight. Do not heat. Take 1 cup of the sample and place it in a sturdy bag or plastic container.
Fill out the form completely and attach a check, payable to Penn State University. Note that there is an additional fee for the test for organic matter. Mail the sample and the form to Penn State Agricultural Analytical Services Laboratory, Tower Road, University Park, PA 16802.
By: Michela Centinari
Denise Gardner, Penn State Enology Extension Associate, and I visited the Lake Erie region, Northwest of Pennsylvania, on June 25 and 26, 2015. We first visited the Lake Erie Regional Grape Research and Extension center (LERGREC) and later met with wine grape growers and winemakers at the South Shore Wine Company. The second day I visited three vineyards with our hosts Andy Muza, the horticulture Extension agent in Erie County, Bryan Hed and Jody Timer, research technologists at Penn State that focus on plant pathology and entomology, respectively.
Regional visits are always a great opportunity to connect with growers and winemakers, discuss production issues, gather information on topics of interest for future educational workshops, and also to learn about grower/winery relationships.
The wine industry in the Northwest region of Pennsylvania is growing, both in size and reputation. Most of the growers I met are experienced juice grape growers transitioning to wine grapes. One of the growers pointed out that he chose, among his 200 acres of existing Concord vineyards, the very best location to plant and grow his Vitis vinifera wine grapes. He had a clear understanding of how site selection is critical to successful cultivation of V. vinifera varieties, and site selection is one of the key areas we discuss with growers upon entering the wine grape industry.
During the two-day visit, most of the discussion focused on winter injury sustained by V. vinifera, inter-specific hybrids and also V. labrusca/native grapevines (mostly Niagara) over the past two winters. The last two years provided record low temperatures in Erie area during the 2013-2014 and 2014-2015 winters, which have proved challenging for farmers (Figure 2). Variation in cold hardiness among grape genotypes, the impact of a diversified crop, and vineyard management practices to reduce/minimize future winter injury losses were discussed to great length.
Growers have been busy assessing the extent of winter injury, training suckers to be used as new trunks and cordons (Figure 3) and making re-planting decisions. One industry member pointed out that winter injury losses have forced growers to make strategic decisions in terms of variety selection. It was recommended that growers use this opportunity to substitute varieties that did not produce well with others that are more suited for the region and individual vineyard sites. In terms of crop diversification, the use of cold-hardy hybrid varieties released by the University of Minnesota may be a viable option for growers, but wineries should be consulted with regards to their interest in those varieties. Local market opportunities still need to be explored in Pennsylvania with regards to cold-hardy hybrid variety sales in the tasting room.
From a research prospective, these two consecutive severe cold winters provided a good opportunity to evaluate the cold hardiness of V. vinifera and inter-specific hybrid wine grape varieties at the variety evaluation planting established at LERGREC in 2008, as part of the NE-1020 multistate project. For more information about the NE-1020 trial, please refer to the article “NE-1020… What? The Top 5 industry benefits affiliated with the NE-1020 variety trial” by Denise Gardner.
During our visit we noticed, as expected, further damage to the cold tender V. vinifera varieties. Among the V. vinifera, Grüner Veltliner and Cabernet Franc are recovering better than Pinot Grigio and Pinot Noir, which are either dead to the ground or showing a weak recovery (Figure 4a, b). Very good bud survival was observed in Chancellor (Figure 4c) which produced about 3-4 clusters per shoot despite the extremely cold events recorded over the last two winters. Overall, Marquette, a cold-hardy hybrid variety released by the University of Minnesota, has shown encouraging results. In addition to the cold sensitive V. vinifera varieties, a poor survival was observed in the NY81.0315.17 (Riesling x Cayuga White) selection (NE-1020 vineyard) and in Traminette at several vineyards within the Erie region (Figure 4d).
Protecting vines and fruiting potential from winter injury
Growers had several questions about best practices to protect trunks and the fruiting potential of the vines against winter injury.
Hilling up the soil around the vines in the fall and taking out hills in the spring is the most common practice used by growers to protect the graft union and some of the scion tissues above the graft union against low winter temperatures. A few growers showed concerns about the wet conditions of the soil in the fall/spring which makes this operation difficult. Heavy, wet soil may be thrown up under the trellis in large clods which can result in imperfect burial of the vine trunk, and makes the take-out operation difficult . Other growers mentioned using straw, or hay, or plowing snow (if there is sufficient snowfall) around the vines to insulate vine tissues. In the spring, it is critical to remove the soil around the graft union to avoid scion rooting, which defeats the purpose of rootstock and may result in vine decline .
Burying sucker canes under the soil or straw in the fall is a method that can be used to avoid winter injury and insure the retention of a ‘marketable’ crop the following year. A comprehensive description of the ‘burial cane’ technique can be found in: Winter Injury to Grapevines and Methods of Protection, Extension bulletin available for $15. Growers in Ontario and in New York State used this technique to protect some fruiting potential of the vines. As a brief explanation, shoots are grown on wires near the ground during the growing season and they are covered with soil or straw in the fall (Figure 5). Another option is to place canes near the ground after the vines go dormant. “A wire on the ground that is tensioned either permanently or temporarily is very helpful to hold canes near the ground” . The buried canes need to be extracted from the soil as soon as the risk of low winter temperatures is past.
The cane burial technique and its effects on vine bud survival and production have been examined at Cornell University with the help of cooperating growers of V. vinifera varieties. For detailed information on the study please check Understanding and Preventing Freeze Damage in Vineyards: Workshop Proceedings (21-38) .
The main finding in this study was:
- Sucker canes buried in the fall do avoid the freeze injury suffered by the aerial canes of the vines.
- After canes were unburied, buds appeared to suffer injury unrelated to freezing. Buried canes showed more “blind nodes,” they were less productive (e., significantly fewer clusters) than canes not buried. Buried canes also showed a delayed bud and shoot emergence compared to aerial, not buried canes.
- Cane burial is not a cheap operation: “typical extra costs per acre for cane burial in the Finger Lakes Region is about $400 to $500. This includes labor needs for laying out ground wire, wrapping them with suckers, hilling, and buried cane extraction, pruning, and tying in spring” .
- “In normal or warm years, burying cane can result in production and economic losses. However, in extremely cold winters, buried canes allow a “half crop” and no dead vines” .
- Zabadal, TJ, Dami, IE, Goiffinet, MC, Martinson, TE, and Chien, ML (2007) Winter Injury to Grapevines and Methods of Protection. Extension Bulletin E2930. Michigan University Extension.
- Goffinet, MC (2007). Grapevine Cold Injury and Recovery After Tissue Damage and
Using Cane Burial to Avoid Winter Injury. In: Understanding and Preventing Freeze Damage in Vineyards, Workshop Proceedings. University of Missouri Extension. 21-38.
By Michela Centinari
It seems like yesterday we were looking at the weather forecast and worrying about cold winter temperature events and the potential for grapevine injury. Now that it is finally starting to get warmer here in Pennsylvania, we may be faced with another threat: spring frost. A grape grower is never bored!
It was another cold winter in Pennsylvania, particularly harsh in the Lake Erie region (Figure 1). At the Penn State Lake Erie Regional Grape Research and Extension Center (LERGREC) temperatures bottomed out at about -21 °F (-30 °C) on February 16, 2015. Unfortunately several cold events (-13, -14 and -15°F) were recorded over the following ten days. On a ‘positive’ note, the week before these extreme cold events, temperatures were lower than normal, with daytime temperature highs well below freezing, except for one day (34°F). These temperatures may have provided a positive, reinforcing maintenance of the vines’ mid-winter cold hardiness . Bryan Hed and the LERGREC’s crew have been checking the extent of bud and trunk damage on Concord and other hybrid varieties.
Information available on cold winter injury on grapevine
At the 2015 Mid-Atlantic Fruit and Vegetable Convention I reviewed the factors that can affect grapevine cold hardiness, explained how to assess bud, cane and trunk cold damage, as well as how to manage cold-injured vines. For information on grapevine cold injury you can refer to the Grapevine cold injury, end of the season considerations blog post and references within.
If you are looking for specific information on winter injury to vine phloem you can check this recent and comprehensive review: Viticulture and Enology Extension News, spring 2015, Washington State University written by Michelle Moyer (Assistant Professor and Viticulture Extension Specialist at Washington State University).
Percentage of winter injury does not equal percentage of crop loss
In March, I attended The Northern Grapes Project Symposium in Syracuse, NY. Tim Martinson (Senior Extension Associate at Cornell University) and Imed Dami (Associate Professor and Viticulture Extension Specialist at Ohio State University) highlighted that the percentage of bud cold damage does not always equal percentage of crop loss. The answer often lies in the pruning adjustment strategies adopted by growers. Dami reported that, despite 40% of bud winter damage, Marquette produced about 5 tons/acre in Ohio last year. Those vines were pruned to 5 bud-spurs (‘hedge pruning’) to compensate for winter injury . .
Tim Martinson reported that last year many growers in the Finger Lakes region (NY) left more buds to compensate for winter injury experienced during the 2013-2014 winter. The growers left up to five-fold more buds than they would have done in a normal year. Many cane-pruned VSP vineyards were spurred to 5-6 bud spurs. It was a pleasant surprise that in 2014 widely planted V. vinifera varieties such as Riesling, Chardonnay, and Cabernet franc, came through better than was expected based on bud mortality estimates. I know that many growers prefer cane pruning, and I understand the reasoning behind that, but please take into consideration that cane pruning is not recommended following winter injury .
How to train suckers of cold injured vines?
Imed Dami recommends that growers “actively” train vines back to their original training system in the same season in order to resume production quicker. Therefore, instead of training suckers vertically (they can become extremely vigorous!) they should be trained horizontally along the fruiting wire. With extremely vigorous vines, four shoots should be selected and then two can be laid horizontally on the fruiting wire. With less vigor, two shoots can be selected and laid horizontally, one to each side. Then, shoots should be tipped to stimulate lateral shoot growth. Lateral shoots growing vertically and upward will become the future spurs next season . Latent buds on the lateral shoots will develop like buds from primary shoots. As long as they are exposed to sunlight and clean from disease and insects, they should have the same cold hardiness as any other buds.
Here is a valuable video regarding pruning with regards to cold injured vines: https://www.youtube.com/watch?v=r1Yhv8Rw38o
A few words on spring frost
As we get close to bud-break, the threat of spring frost is approaching. In the spring of 2014, no frost damage was recoded in grapevines in Pennsylvania and hopefully we will have another frost-free spring. If you would like to get information about frost protection strategies you can check the following websites and newsletters. Unfortunately, there is no new exciting or infallible frost protection method. Site selection remains the best way to protect vines from frost injury.
- Frost Injury, Frost Avoidance, and Frost Protection in the Vineyard, eXtension website, by Ed Hellman, Texas AgriLife Extension
- The ABCs of Frost Management by Robert Evans, Supervisory Agricultural Engineer with the USDA-ARS (retired)
- Viticulture Notes Vol.30, April 2015 by Tony Wolf, Professor and Viticulture Extension Specialist at Virginia Tech University
- Comprehensive presentations on active and passive frost protection strategies can be found at the University of California, Davis Cooperative Extension website
To the often asked question: If my vine gets frosted, should I remove the injured shoots?
The answer is: “There’s not much of a point,” according to Tony Wolf, Professor and Viticulture Extension Specialist at Virginia Tech University. A detailed explanation on how to handle damaged shoots and potential consequences on yield production can be found at Viticulture Notes, Vol.25, May-June 2010
Testing the cryo-protectant properties of KDL
KDL (potassium dextrose lactose; Agro-K corporation, Minneapolis, MN, USA) is a potassium based fertilizer. According to the manufacturer’s literature, spraying KDL shortly before a frost event (24-48 hours) would increase the potassium and sugar levels within the plant and reduce the frost injury on young vine tissue. Although attractive to growers, there is not scientific literature that supports the effectiveness of this product in preventing/reducing frost damage. Numerous grower testimonials are available, but growers usually do not leave an ‘untreated’ control area where the material is not applied, which is critical in order to evaluate the efficacy of KDL as cryo-protectant.
A large scale study coordinated by Tim Martinson (Cornell University) and in collaboration with the Agro-K company (KDL manufacturer) has been set up this spring to evaluate the effect of KDL at several vineyard sites located in NY and PA. Penn State is a collaborating university that is helping to work with six commercial growers that agreed to participate in the study in addition to the Penn State LERGREC in North East, PA.
Although, I’m hopeful there will not be a spring frost that growers have to deal with, if we do end up with a spring frost during the 2015 growing season, this study will hopefully provide some useful recommendations for grape growers.
- Wolf T.K., 2015. Viticulture Notes. Vol. 30 supplement, 17 February 2015
- Dami, I.E. , Ennahli S., Zhang Y. (2012). Assessment of winter injury in grape cultivars and pruning strategies following a freezing stress event. American Journal of Enology and Viticulture, 63: 106-111.
- Dami, I.E. 2009. Ohio Grape-Wine Electronic Newsletter Vol.3: 2-5, 6 Feb 2009.
- Dami I.E., 2014.Ohio Grape-Wine Electronic Newsletter, Vol.25, 3 July 2014.
By: Andy Muza
Penn State Extension – Erie County
Last week Bryan Hed discussed pre-bloom disease management. This week I will provide a preview of insect pests that may cause problems in the vineyard from bud swell through the immediate pre-bloom period. I will not be providing choices of insecticides registered for use in Pennsylvania for each pest but instead strongly suggest that each grower purchase a copy of the 2015 New York and Pennsylvania Pest Management Guidelines for Grapes. This guideline provides a wealth of information on insect, disease and weed management with specific pesticide recommendations, as well as, a chapter on sprayer technology. Growers interested in organic management of pests can download a copy of Cornell’s 2014 Production Guide for Organic Grapes.
Another valuable, compact resource that can be taken along in the vineyard as you are scouting is A Pocket Guide for Grape IPM Scouting of Grapes in North Central & Eastern U.S. This guide provides concise information along with color photographs on insect/mite pests, natural enemies, diseases and disorders.
Grape flea beetle – beetles are small (3/16”) and metallic blue in color. Beetles overwinter in the adult stage and emerge as grape buds begin to swell. The most significant injury caused by this pest is due to adults feeding on swollen grape buds, often consuming enough tissue to destroy the developing bud. By about 1/2” growth the threat of economic loss from this pest is over. Larvae feed on leaves but the extent of injury is usually negligible.
The largest populations of flea beetles are most often around wooded or overgrown edges of vineyards. Scout vineyard rows bordering these areas frequently during the bud swell stage. Look for injured buds along canes and presence of adults. Beetles will jump like fleas when disturbed. Warm, sunny days are usually the best opportunity to observe adults. Areas with bud injury of 2% or greater would warrant an insecticide treatment.
Climbing Cutworm – several species of cutworm larvae feed on grape buds during the swell stage. The injury to buds can be confused with grape flea beetle damage. The larvae are immature stages of noctuid moths. Larvae have a brown to gray coloration with darker stripes or dots along the body. Larvae hide under stones or weeds beneath vines during the day and climb vines to feed at night. Vineyards with weed cover under the trellis and areas with sandy soils are at greater risk for injury. Scout frequently during the bud swell stage. If bud injury is detected when scouting then examine weeds/soil beneath vines for presence of larvae. Areas with bud injury of 2% or greater warrant an insecticide treatment.
3 – 12 INCH SHOOT GROWTH
Banded Grape Bug and/or Lygocoris inconspicuous – both of these insects have piercing and sucking type mouthparts and are in the same family (Miridae) as tarnished plant bug. Banded grape bug nymphs have antennae with black and white bands, green/brown bodies and are <1/2”. Lygocoris inconspicuous nymphs are slightly smaller with light green antennae (no bands) and light green bodies. Nymphs (immature stage) of both insects feed on developing flower clusters by piercing florets, pedicels and rachises. Although these insects are occasional pests, research by Greg Loeb (Cornell) showed that population levels >1 nymph/10 shoots can cause economic yield losses.
Begin scouting when shoots are 3 – 5” in length and continue until shoots are at least 12”. According to Loeb, flower clusters should be checked on 100 shoots per block with an emphasis near vineyard edges. Due to their body coloration these insects are difficult to see. To determine nymph numbers, hold a white paper plate beneath clusters then tap clusters to dislodge insects. If levels are >10 nymphs/100 shoots an insecticide application is suggested. See scouting video – Banded Grape Bug LERGPvids https://www.youtube.com/watch?v=FrEJ6IJB_is
Grape Phylloxera (leaf form) – phylloxera are native to the eastern U.S. and cause galls on both leaves and roots of grapevines. The life cycle is different for the foliar and root forms of this insect. The root form is the most destructive of the 2 forms but is managed by grafting susceptible varieties (e.g., Vitis vinifera) to phylloxera-resistant/tolerant rootstocks.
Nymphs (crawlers) emerge in the spring and move to shoot tips to start feeding on the upper leaf surface of newly developing leaves. Feeding initiates the formation of galls on the lower leaf surface. Females can lay hundreds of eggs within galls throughout their life. Crawlers hatch from galls on the upper leaf surface, move to and feed on developing leaves, initiating new galls. This cycle continues throughout the season.
Grape varieties vary widely in their susceptibility to leaf galling by phylloxera. Some varieties (e.g., Chambourcin, Seyval, Vidal) can suffer severe leaf galling which reduces leaf function and can affect shoot growth.
Begin scouting early in the season, especially in highly susceptible varieties or newly planted vineyards. Galls may become evident as soon as the 3-5 leaf stage so carefully examine the undersides of terminal leaves for warty looking, green to reddish growths. An insecticide application can be applied when first galls are forming. Additional sprays may be needed 10 -14 days later if galls are present on new leaf growth. Correct timing of sprays is important because nymphs (crawlers) must be active and feeding on leaf surfaces for insecticides to be effective. The most reliable method to determine if crawlers are active is to cut galls open and observe for presence of nymphs. Crawlers are extremely small so a good hand lens is needed.
Additional Insect Pests – During this time period a number of other insects (i.e., grape plume moth, grapevine epimenus, 8 – spotted forester, tumid/tomato gallmaker, grape cane gallmaker, and grape cane girdler) may also be present in the vineyard. Although injury from these insects may look alarming, damage is usually cosmetic and insecticide applications are rarely needed. (See sites for fact sheets below).
Rose Chafer – rose chafer beetles are about 1/2” long, with tan colored bodies and long, spiny legs. These beetles feed on a wide variety of hosts including grape. Large numbers of beetles often emerge from the soil at the same time (about 10 days before grape bloom) and begin feeding on tender flower clusters and leaves. Infested areas can lose extensive numbers of flower clusters if beetles are not detected early and treated.
Vineyards with a history of this pest or blocks with sandy soils should be scouted daily beginning at least 10 days before bloom. A fact sheet on Rose Chafer from Ohio State ( http://www.oardc.ohio-state.edu/grapeipm/rose_chafer.htm ) recommends an insecticide application if a threshold of 2 beetles per vine is reached.
Fact sheets on grape insect pests can be found at the following sites:
Please click on the links below for more fact sheets specifically on insect pests found in the vineyard:
By: Bryan Hed
Well spring is here, and with a new season of grape production soon upon us, a review of pre-bloom disease management topics is in order. In addition to adjusting and carefully calibrating sprayers, take some time now, before bud-break, to acquaint yourself with the NEWA website (Network for Environment and Weather Applications) found at http://newa.cornell.edu . This website gives you easy access to a wealth of weather and pest forecast information from an extensive network of weather stations positioned all over the Northeast…and it’s free. When you first access the site, you’ll see a map of the northeastern U.S. You can use your cursor to navigate the map and click on the weather station nearest you (denoted by a leaf/rain drop icon) to tap into daily and hourly weather (temperature, rainfall, leaf wetness duration, wind speed, etc) near your vineyard or any location you choose (hmm, we had 21 below zero on February 16, I wonder how badly southern PA was hit…). Clicking on ‘grapes’ under ‘crop pages’ will give you access to disease forecasting models for the ‘big four’ like Phomopsis cane and leaf spot, black rot, and powdery and downy mildew. You can also access the grape berry moth degree day model that will help to take a lot of the guesswork out of timing your berry moth insecticide sprays later this year. Each model forecast is accompanied with disease management messages and explanations. For example, at our present stage of development, ‘dormant’, the website has this to add about Phomopsis control: ‘Dead and diseased canes, arms, and pruning stubs should be pruned out to reduce inoculum. Dead canes and stubs can produce extremely high levels of Phomopsis spores over several years. In particular, growers seeking to minimize fungicide use should pay strict attention to the removal of infected wood from within the canopy’. This is a great way to educate yourself on the challenges ahead as we strive to make the most effective and cost worthy decisions in our efforts to grow healthy grapes. Check it out!
For many of us, Phomopsis cane and leaf spot will be the first fungal disease we encounter during the early shoot growth stages in late April (?) and May. I have included several pictures below to help reacquaint you with symptoms on shoots, canes, and leaves. This fungus is often a threat during those long rain periods in May. Young shoots are capable of becoming infected as soon as they emerge and inflorescences ($) can be impacted by this pathogen around the 3-6” shoot stage (basically when they become visible). Infections on newly emerged inflorescences can literally ‘bite off’ whole sections of the cluster and reduce crop potential very early in the season. Early infections on flower stems can move into berries later in the season, during ripening, and cause fruit drop or even fruit rot (either way, you lose). So, If weather is wet at this stage (3-6” shoots), an application of mancozeb, ziram, or captan will limit these infections that can lead to early destruction of clusters or sections of clusters, fruit rot, and ultimately, reductions in yield. Work by Wayne Wilcox has shown that this fungicide application can significantly increase yields and easily pay for itself (sprays at this time are generally pretty inexpensive). This spray can also protect against early shoot infections that become a source of inoculum (canes) in the following year. So, fungicide applications at the 3-6” shoot stage double as an insurance policy against crop loss in subsequent years.
For symptoms on wood (below), look for scabby lesions on the first 2-4 internodes of year-old canes (from last year’s infections in early May), and/or an abundance of old pruning stubs and older and dead wood.
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).
Sprays for powdery mildew will likely be necessary at very early shoot growth stages for highly susceptible Vitis vinifera cultivars and/or where control of this disease was lacking the previous summer. Research at Cornell has shown that vineyards harboring high overwintering inoculum levels may require that control measures commence earlier the following season to avoid epidemic development and crop loss. A tenth of an inch of rain with temperatures above 50 F constitute a primary infection period for powdery mildew. Materials like sulfur, oils, Nutrol, and potassium bicarbonate materials may be good first choices for mildew at this stage. Keep in mind that you can’t mix sulfur and oils, or oils and captan (read the labels!). For juice grapes like Concord and Niagara, powdery mildew control is generally not a concern at this time.
For black rot, old fruit mummies and clusters (infected from the previous season) are prime sources of inoculum in spring and early summer, and thorough removal of all this material from the trellis during dormant pruning is essential to maintaining good control of this disease. Once on the ground, mummies can be buried with cultivation or mulch, reducing or eliminating their capacity to fuel new infections in spring. A fungicide application for black rot may not be necessary at these early shoot stages if good control of this disease was achieved the previous year and conscientious trellis sanitation has been implemented. On the other hand, inoculations we performed at these early shoot growth stages (simulating wet weather and an overwintering inoculum source in the trellis) can produce leaf and shoot infections in the cluster zone, that go on to release spores during early berry development stages, and that result in fruit infection and crop loss. An application of mancozeb, ziram, or captan for Phomopsis will also provide control of early black rot infections.
At about 10-12” shoot growth or the 5-6 leaf stage, a fungicide application at this time will limit infections of Phomopsis on shoots, and cluster and berry stems, especially in vineyards at high risk. Black rot control may not be critical for juice grapes at this time if excellent control of this disease was maintained in previous years and conditions are dry. However, it would be advisable to apply a fungicide for black rot if conditions are wet and warm, especially to Vitis vinifera and susceptible hybrids. As mentioned earlier, black rot leaf and shoot infections at this time can increase inoculum levels in the cluster zone, making black rot control more problematic during the fruit protection period (after capfall). If scouting reveals black rot lesions on leaves in the cluster zone, this is a great big red flag! Make sure your subsequent black rot sprays are effective and timely, especially during the fruit protection period. Downy mildew becomes a concern at this stage as well and fungicide sprays for this disease will be necessary for susceptible varieties, especially if conditions are wet. Mancozeb products offer one of the best control options for all three diseases. Ziram is a little weaker on downy mildew, and Captan a little weak on black rot, but these may also be an option if these diseases are not a priority at this time.
Powdery mildew is less of a concern at this time for juice grapes than for wine grapes, but may be necessary if susceptibility and risk of disease is high, especially for growers of Vitis vinifera and sensitive hybrid wine grapes. Sulfur is an inexpensive option for powdery on non-sensitive varieties. The sterol inhibitor fungicides may also be good choices at this time, providing they are still effective in your vineyard. Note that the sterol inhibitor and strobilurin fungicides have been in use for many years in Pennsylvania vineyards and are considered at high risk for the development of resistance by the powdery mildew fungus, that is, they may not be as effective as they used to be, or are ineffective. If you suspect powdery mildew resistance to these materials in your vineyard, either apply them in a tank mix with another active ingredient for mildew (like sulfur) or discontinue their use and use an alternative active ingredient. This is even more critical for the next two fungicide application timings; the immediate pre-bloom/first post bloom sprays.
Immediate pre bloom/first post bloom fungicide application.
These next two sprays – immediate pre bloom (just before the beginning of capfall) and first post bloom – are critical for every vineyard, every year, for control of every disease!!! Young fruit of every variety are most susceptible to all the major diseases (Phomopsis fruit rot, black rot, downy and powdery mildew) during the period from bloom to about 2-3 weeks after bloom. Apply your most effective materials (Strobies (if no resistance issues), Quintec (powdery only), Manzates/Ziram/Captan (for Phomopsis, black rot, downy mildew)). This is also the perfect time to consider some of the newer products like Vivando or Torino (for powdery mildew only), Revus Top (for powdery and downy mildew and black rot), Inspire Super (for powdery mildew and Botrytis), Luna Experience (wine grapes only, for powdery mildew, Botrytis, and black rot) and the newer downy mildew materials (listed below). Plan to apply for best coverage, every row, full rates, and shortest intervals (NEVER extend the interval between these sprays beyond 14 days).
Phosphorous acid products (aka phosphites, phosphonates) have become favorites for many growers as a means of controlling downy mildew. They are effective and ‘friendly’ to work with. However, if you use these materials at this time, be mindful that, although they are extremely rain-fast, they still provide only limited protection against new infections. Do not expect phosphorous acid sprays to provide more than 10 days of protection, especially under high disease pressure.
Relatively new downy mildew materials
- Revus; contains mandipropamid, registered in 08. Very effective on downy mildew in PA and NY trials.
- Presidio; fluopicolide, registered in 08. Very effective on downy mildew in PA and NY trials. Label requires that Presidio be applied as tank mix with another downy mildew fungicide.
- Reason 500 SC; fenamidone, which is a quinone outside inhibitor; same mode of action as strobies, but not technically a strobie. However, treat it as a strobie with respect to resistance management. Provided excellent control of downy mildew in Cornell trials.
- Quadris Top; azoxystrobin + difenoconozole; for downy and powdery mildew, black rot, and Phomopsis. New combination of current chemistries. Its use on grapes in the Lake Erie region will be greatly restricted: with azoxystrobin in the mix, this can’t be used in Erie county PA, and with difenoconazole in the mix, this can’t be used on Concord.
- Ranman; cyazofamid, a new chemistry for downy mildew. PA and NY trials show good to excellent efficacy against downy when applied alone and mixed with phosphorous acid.
- Zampro; ametoctradin + demethomorph. The newest of the new downy mildew materials; a combination material that is very effective on downy mildew.
A new material, Aprovia, may be available for 2015 (?), mainly for powdery mildew. Federal registration is anticipated in April of this year. This material is related chemically to Boscalid (found in Endura and Pristine) and Fluopyram (found in Luna Experience).
And finally, a short recap of some main points – in no particular order of importance – when planning your pre-bloom disease management programs…
- Overwintering inoculum control = maintaining a relatively clean vineyard through to harvest (in the previous year) and subsequently, thorough sanitation during dormant hand pruning activities.
- Good overwintering inoculum control will make seasonal disease control more forgiving (‘I can’t get a spray on because it won’t stop raining; good thing I controlled diseases well last year!!’); consider it an insurance policy. Your pre-bloom spray programs will also be more effective as they are applied to control a smaller initial pathogen population this year.
- Early spray programs are relatively inexpensive. If disease control was lacking last year, higher overwintering inoculum levels will require that you fire up your seasonal spray program earlier this year, especially if conditions are wet.
- The bloom and early post bloom periods are the most critical for protecting your crop ($) against all diseases; it is never cost effective to cut corners during those stages of crop development.
- Scout your vineyards and develop your skills at identifying diseases; know what it is you’re trying to control. Focus your scouting efforts in vineyards/vineyard areas where disease control has been most challenging (where you expect disease to show up first). Discovering disease in its earliest stages is key to controlling it, and you can’t discover it early if you don’t scout!
- Know your fungicides; their strengths and weaknesses, the specific diseases each material controls, and their rotational partners for resistance management.
- Read labels!
- Prepare yourself to make the most of the 2015 growing season with a run through the NEWA system.