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Tips for late season downy mildew control

By: Bryan Hed, Plant Pathology Research Technologist, Erie County

At this time of year, it’s so important to continue scouting leaves for the distinctive white ‘downy’ sporulation of downy mildew. Growers of susceptible varieties need to keep closely monitoring their vineyards for active sporulation and use that information in combination with the DMCast model on NEWA.

The presence of active white sporulation on the undersides of leaves means the downy mildew pathogen is capable of spreading quickly under wet conditions and can spiral out of control, strip vines of their leaves and effectively end the season (and the ripening of canes for next year’s crop).

If you find yourself trying to control this disease well into the ripening period, be aware that your list of chemical control options will start to become shorter as we get within 30 (Ranman, Reason), then 21 (Ziram, Presidio (only older stocks; can’t purchase new material anymore)), then 14 (Revus, Revus Top, Zampro) days of harvest, until in the end you’ll be left with some formulations of Captan, copper, and phosphorous acid products (0 day pre-harvest interval).

Its also important to remember that materials like Ranman, Reason, Revus/Revus Top, and Zampro contain chemistries that are prone to the development of resistance. These materials should not be used to put down an epidemic, which will speed up the resistance development process. And, although phosphorous acid products are less prone to resistance development, you will enhance the chances of losing this technology to resistance as well, by using these materials on a heavily diseased vineyard.

Also, limit your use of phosphorous acid products to three applications per season. On the other hand, fungicides like Captan or copper formulations would be least risky in terms of the development of resistance and can be an effective means of controlling downy mildew late into the growing season.

Just be mindful of varieties that may be injured by copper applications, and that copper injury will be exacerbated by application under slow drying conditions and application to wet canopies (for example, don’t make applications to dew covered canopies in the early morning). If you are protecting a non-bearing, young vineyard from downy mildew (you’re not selling/harvesting a crop), you can continue to use mancozeb products past the 66-day pre-harvest interval.

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​Viticultural considerations during bloom and early fruit development

In this week’s blog, you will find updates and information from several of our authors with an emphasis on disease and insect management and vine nutrient status.

Bloom and early fruit set disease management

By Bryan Hed, Department of Plant Pathology and Environmental Microbiology, Penn State Extension

Well, the 2018 season has gone from 0 to 100 mph over the past four weeks, and grapevine shoots are currently growing at a rate of at least an inch a day. Trying to keep grape tissue protected with pesticide sprays can be a bit of a challenge when canopies double or triple in size each week. However, now it’s time for the most critical fungicide applications of the season; the immediate pre and post-bloom sprays. This is your annual reminder. Fruit ($$) of all grape varieties are most vulnerable to infection from all the major fungal diseases at this time (black rot, Phomopsis, powdery and downy mildew), and in many places across Pennsylvania the previous 4 weeks have been warmer and wetter than average; the perfect setup for fungal disease development on fruit. There’s no more critical time to “spare no expense” than immediately before bloom to about 2 weeks (juice grapes) to 4 weeks (wine grapes) after bloom. Use best materials, apply for best coverage, and allow no more than 10-14 days between these next 2 to 3 sprays. At this time, do not rely on materials that we know are slipping in efficacy, or have already slipped in efficacy, due to the development of resistance in many parts of the East (ie, strobilurins and sterol inhibitors).  

When I hear from growers that have experienced problems with fungal fruit infection in the past, breaches in disease control are most often traced to the period of grapevine development around bloom.  Some common mistakes include: i) use of the wrong materials (there was resistance to what they used, their mix didn’t cover all diseases, their choice of materials wasn’t very effective, etc), ii) stretching of spray intervals (more than 10-14 days between the immediate pre and post bloom spray), iii) less than optimal coverage (canopies were too dense, canopy management was lacking, sprayers weren’t adjusted for maximum coverage, etc), iv) taking a vacation from farming during this period of time (all of the above?).

If you’re growing bunch rot susceptible wine varieties, fruit-zone leaf removal around or shortly after bloom, can improve coverage and create a fruit-zone environment that is less favorable for the growth of fungal pathogens (For more detailed information see: Early season grapevine canopy management, Part II: Early leaf removal). Strict pre-bloom sucker control can delay the rise of diseases like downy mildew and black rot that emanate from the vineyard floor. Pre-bloom shoot thinning, while shoots can be easily removed by hand, will not only balance canopies with yield but also improve the efficacy and value of fruit protection sprays. Proper weed control/maintenance of row middles and cover crop height can reduce humidity in the vineyard and improve drying time of plant surfaces after rainfall. Integrating these cultural practices into your pre-bloom crop management plan will greatly assist your fungicide applications toward maximizing fruit disease control during bloom.

For more details on the various diseases and how to deal with them during this critical fruit protection period, you may find it convenient to check out previous posts from April 7 and June 16, 2017:

https://psuwineandgrapes.wordpress.com/2017/04/07/2017-pre-bloom-disease-management-review-and-discussion/

https://psuwineandgrapes.wordpress.com/2017/06/16/2017-summer-disease-management-review/

Insect updates on Grape Berry Moth and Spotted Lanternfly

By Jody Timer, Entomology, Lake Erie Grape Research and Extension Station

Grape Berry Moth (GBM):  The first grape berry moth for the season usually appear at about 150 degree days from January 1st.  This year, in the Lake Erie Grape growing region, we had a late spring which resulted in a later-than-usual emergence of GBM (around May 15th). The emergence occurred much earlier for the growers in the Southeastern portion of the state. The research we have done in the past indicates that spraying for GBM prior to the first full generation (not this emerging generation) is more effective and will not adversely affect yields at harvest.  So this generation, which starts to peak at wild grape bloom and continues for about 10 days, does not in most cases need to be sprayed. Wild grape bloom in the Lake Erie Grape growing region occurred around May 30th, it was as early as May 13th in the southeastern regions of PA.  Wild grape bloom is used as the biofix for the NEWA system to start accumulating degree days. This system uses the GBM phenology model to recommend optimal spray timings for GBM   http://newa.cornell.edu. It is important that you keep track of when wild bloom occurred in your area to allow the model to precisely track the GBM phenology. If you missed the wild bloom date, the NEWA system will calculate wild bloom for your area based on historical data. The best way to determine infestation of your vineyard is to scout for damage. This generation of GBM produces webbing on the flowers and clusters. This webbing, although harder to scout for than later berry damage, is a good indication of severity in the ensuing generations. If your vineyard has high GBM consider spraying more often during the upcoming generations.  Grape berry moth can cause considerable damage to vineyards through berry damage and late season rots.

Screenshot 2018-06-09 06.21.31

Spotted Lanternfly (Lycorma delicatula): This new invasive insect was first discovered in Bucks County in 2014, the affected area was placed under quarantine to prevent the movement of the insect and its egg masses. Prior to its discovery in the fall of 2014, the spotted lanternfly had not been found in the United States. This fall, when the adults were flying and laying eggs, the quarantine area saw considerable increases and movements of the population. As a result, the quarantine area has been expanded to include all of the counties in southeastern PA. There has also been a colony found in Virginia.  Spotted lanternfly host plants including fruit trees, ornamentals, hardwood trees, and grapevines. These insects are exhibiting a preference for tree of heaven (Ailanthus altissima) and vines including grapevines.  Spotted lanternfly has the potential to cause substantial damage. Some have estimated potential crop losses, which includes Pennsylvania apples, grapes, and hardwoods, at $18 billion dollars. While feeding on and damaging their host plants, spotted lanternfly also ejects a liquid called honeydew which causes sooty mold and attracts secondary insect pests. Spotted lanternfly overwinter as egg masses, which are small (about 1-4”) and greyish white. They somewhat resemble a dirt splatter.

Screenshot 2018-06-08 19.46.04

The first nymphs began to hatch in late April or May and complete four instars.  These nymphs are 4-9 mm long and wingless with black with white spots. The fourth instar develops red patches, and then emerge into adults in late summer.  This time of the season it is important to scout for egg masses, which although hatched, would indicate an infestation in your area. The black and white nymph stage will be present now.Screenshot 2018-06-08 19.47.35

There is a team of state, federal, and local public officials, academic researchers, and extension personnel working on the problems dealing with this insect. It is important to report findings of spotted lanternfly is you are not in the quarantine area. The website: https://extension.psu.edu/spotted-lanternfly as well as the PDA website has important information on this insect and includes numbers to call if you find insects outside of the quarantine area.

Assessing vine nutrient status

By Dr. Michela Centinari, Assistant Professor of Viticulture, Department of Plant Science

Proper vine nutrient management is crucial for the vineyard longevity, as it helps ensure adequate vegetative growth, fruit set and growth, and optimum wine quality. While some nutrients up-taken by the vine are recycled through fallen-leaves decomposition, the majority of nutrients leave the vineyard in harvested fruit, pruned-wood material (if the brushes are not chopped and left in the vineyard), or through leaching and runoff.  Assessing vine nutrient status should be a routine practice and used not just to confirm a suspected nutrient deficiency.

To determine vine nutrient status in an established vineyard, plant tissue nutrient concentration should be analyzed at bloom and/or later in the season around véraison. A soil test is useful and can provide clarification, but has limited benefit. It will indicate relative nutrient availability, but it does not tell what and how much the vines absorb.

What type of tissue to collect for nutrient analyses

There is a long-standing debate about what leaf tissue (blade, petiole, or the whole leaf) best reflects vine nutrient status and correlates to nutrient requirements for optimum vine growth, yield, and fruit composition. However, in the eastern US, the sufficiency range (or target value) of each nutrient concentration is only defined for petiole tissue.

When to collect grapevine petiole samples for nutrient analyses

Collecting a petiole sample at both bloom and véraison and having it analyzed will provide meaningful insight when developing a nutrient management plan. For example, if you noticed visual symptoms of nutrient deficiency in the previous growing season (Figure 1), a nutrient test at bloom will help determine if there is an actual deficiency, and you will be able to correct it in a timely manner (1).  Nutrient concentrations in leaf tissue tend to be more stable as the season progresses, so taking a sample at véraison is typically recommended compared to taking samples at bloom, especially for routine analysis (1).

Screenshot 2018-06-07 10.50.09

How to collect grape leaf tissues for nutrient analyses

A comprehensive and illustrated guideline on how to collect whole leaf samples (which can also be used for petiole sampling) is on page 12 of the Vineyard nutrient management in Washington State extension bulletin. Be sure to sample each variety separately and to collect 50 large petioles or 100 small ones per variety.

Where to send the samples

Use a reliable lab in your area that has experience in vineyard tissue testing, and use the same lab each year so that the analysis is consistent. If you are in Pennsylvania you can send your plant tissue sample to the Penn State Agricultural Analytical Services Lab.  Please be sure to provide all the information required to interpret the lab results (e.g., type of tissue, time of the year the sample was collected). Lab results will report the concentration of each nutrient analyzed and if its level is low/deficient, sufficient, or too high/excessive. If you need assistance with interpreting your report, contact your local extension for further assistance.  You can find the contact information for your local Penn State Country Office by entering your zip code in the search field on this site: bit.ly/2J9yCPr

Reference: 

  1.  Moyer M., Singer S., Hoheisel G., and Davenport J. Vineyard Nutrient Management in Washington State, EM111e (Bulletin) Washington State University

Comments concerning insect and disease management at this time of the season (Immediate Prebloom – Early Postbloom period)  

By Andy Muza, Penn State Extension – Erie County

I’ll begin by stating that every commercial grape grower in Pennsylvania should have a copy of the 2018 New York and Pennsylvania Pest Management Guidelines for Grapes: https://store.cornell.edu/p-201631-2018-new-york-and-pennsylvania-pest-management-guidelines-for-grapes.aspx   This guideline provides a wealth of information on insect, disease and weed management with pesticide options, rates, and schedules, as well as, a chapter on sprayer technology.

Also, monitoring your vineyard(s) at least weekly throughout the season is critical for managing pests. Frequent scouting will alert you to problems developing in the vineyard and provide the information needed to make informed decisions concerning pesticide applications. (You won’t know what’s out there if you’re not).

Diseases – When thinking about disease management the first thing that commonly comes to mind are fungicide applications. However, cultural practices (e.g. shoot thinning, leaf removal in the fruit zone, etc.) are integral components of a disease management strategy and should be used whenever applicable.

As Bryan Hed mentions and deserves repeating, The Immediate Prebloom (just before blossoms open) through early post-bloom/fruit set period is a critical time for managing fruit infections caused by phomopsis, black rot, powdery mildew and downy mildew. Fungicide protection for botrytis on tight – clustered varieties at bloom (when 80 – 90% of caps have fallen) can also be important in wet seasons.

Insects – Two important insect pests that Jody Timer is covering are grape berry moth and spotted lanternfly. (For additional information on grape berry moth see: Three Phases to Managing Grape Berry Moth  https://psuwineandgrapes.wordpress.com/2017/04/28/three-phases-to-managing-grape-berry-moth/ and Grape Berry Moth: Answers to questions you should be asking about this native pest  https://psuwineandgrapes.wordpress.com/2015/05/15/grape-berry-moth-answers-to-questions-you-should-be-asking-about-this-native-pest/ ).

I will briefly mention 2 of the more widespread, leaf-feeding pests that you are likely to see sometime this season which are grape leafhopper and Japanese beetle.     

Grape Leafhopper – There are several species of leafhoppers in the genus Erythroneura that feed on grape foliage. 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. The greatest risk for economic losses due to grape leafhopper feeding occurs during hot, dry years in vineyards with heavy crop loads and high leafhopper populations. In most years, the majority of vineyards in Pennsylvania should not require an insecticide treatment specifically for management of grape leafhopper.  However, the decision to apply an insecticide should be based on scouting information and threshold levels. (For more detailed information see: Grape Leafhoppers https://psuwineandgrapes.wordpress.com/2017/06/09/grape-leafhoppers/ ).

Japanese Beetle – Adult beetles feed on over 300 species of plants including grape. They prefer smooth, thinner types of grape leaves which are characteristic of many wine grape varieties (e.g., Chardonnay, Traminette, and Vidal Blanc). Feeding injury, depending on severity, can result in leaves having a skeletonized appearance due to consumption of the soft leaf tissues between veins. Research has shown that grapevines can tolerate a fair amount of leaf area loss without detrimental effects. However, no economic threshold level has been established for leaf injury on grapes caused by Japanese beetle.  Since young vineyard blocks, vines in grow tubes and many wine varieties are vulnerable to serious leaf loss by Japanese beetle feeding consistent monitoring is important. (For more detailed information see: Japanese Beetle: A Common Pest in the Vineyard                                                      https://psuwineandgrapes.wordpress.com/2016/07/09/japanese-beetle-a-common-pest-in-the-vineyard/).

GRAPE DISEASE CONTROL 2018, Part 1

Bryan Hed, Department of Plant Pathology and Environmental Microbiology, Penn State Extension

As the new grape growing season commences, this is a good time to revisit some of the fungicide updates that were discussed at grower meetings earlier this year. While these materials are available to growers in most states, some of them have not yet cleared the extra hurdles required for legal use in New York, and in those instances, I make specific mention of that. I hope this blog will be useful for growers in the 2018 season.

FUNGICIDE CHANGES, NEWS, & REVIEWS

First, Aprovia/Aprovia Top. The active ingredient in Aprovia is solatenol (benzovindiflupyr), and while it does not represent a new chemical class for us grape growers (succinate dehydrogenase inhibitor or SDHI) it is a new and improved chemistry. The SDHI fungicides belong to FRAC Group 7, which also includes chemistries in products like Endura and Pristine (boscalid) and Luna Experience (fluopyram). Aprovia was available for use in most states last year but has now been labeled for use in New York as well. As a solo product, Aprovia is very effective for the control of powdery mildew as trials in NY over several years have shown. Trials at Penn State over the past couple of seasons have also revealed some efficacy on black rot, but I would consider it more in line with “suppression” of this disease and I cannot recommend it for black rot control, especially on susceptible varieties. Also, it should not be relied on for significant control of Botrytis, unlike other SDHIs. The label also lists control of Phomopsis and anthracnose, but I have not seen any real proof of that. Penn State has tested this product over two years on Concord, to examine it for any potential crop injury issues to that variety. in comparison to Revus Top, a standard spray program, and an untreated check, there were was no injury to Concord grape from Aprovia, while, as expected, Revus Top caused severe damage to leaves developing at the time of application.

Aprovia Top, on the other hand, is a mixture of two active ingredients: i) solatenol, the active ingredient in Aprovia and ii) difenoconazole, a DMI fungicide with very good to excellent activity against powdery mildew, black rot, and anthracnose. Aprovia Top is also labeled for control of Phomopsis, but again, local experience and published results of trials with Phomopsis is lacking. The label rate for Aprovia Top is 8.5 to 13.5 fl oz/A; 13.5 fl oz of Aprovia Top provides about the same amount of solatenol as 10.5 fl oz of Aprovia; it also provides about the same amount of difenoconazole as 18 fl oz of Inspire Super, but falls a little short of that found in 7 fl oz of Revus Top. Aprovia and Aprovia Top have a 12 hr REI and a 21-day PHI. As with all the products containing difenoconazole, Aprovia Top should not be applied to Concord grape and other varieties on which difenoconazole injury has been reported. This includes Brianna, Canadice, Concord Seedless, Frontenac (minor), Glenora, Noiret (minor), Skujinsh 675, St. Croix (minor), and Thomcord.

Intuity. The active ingredient in Intuity is mandestrobin, and if that sort of sounds familiar, it’s because this is another strobilurin fungicide (FRAC group 11).  Intuity offers protectant and antisporulant activity against Botrytis, for which it is exclusively recommended, though it will provide suppression of powdery mildew, at least where strobilurin resistance has not yet developed. In limited NY and PA trials, Intuity has provided good to fair control of Botrytis equivalent to current standards like Elevate, Vangard, Scala, and Switch. The label rate is 6 fl. oz/A with a maximum number of three applications (two is recommended) and 18 fl oz per season. Do not make sequential applications; rotate with non-FRAC 11 materials (Elevate, Endura, Fracture, Inspire super, Rovral, Scala, Switch, Vangard) and allow at least 20 days between Intuity applications. Intuity is at risk for resistance development by the Botrytis fungus and it is essential that its use is limited to rotations with other, unrelated Botrytis fungicides both within and between seasons to reduce the development of resistance.  Intuity is rainfast within 2 hours of application, has an REI of 12 hours and PHI of 10 days. Do not use Intuity on V. labrusca, V. labruscahybrids or other non-viniferahybrids. Avoid mixing with organosilicone surfactants. Intuity has not yet been cleared for use in New York.

PresidioPresidio has been with us for about 10 years now and is used for downy mildew control, for which it has been very effective. Unfortunately, Valent has pulled the grape use from the Presidio label and any new product will not be legal for use on grapes this year. However, grape growers will be able to legally use up old stock of Presidio with the grape use pattern on the label.

FLINT ExtraA new formulation of an older material, FLINT Extra is a liquid (500SC) formulation that replaces Flint 50WG. The use rate of the new product is the same (in terms of active ingredient) as the old product. In other words, 2 fl oz of FLINT Extra 500SC = 2 oz Flint 50WG. But the new product is labeled to increase the application of active ingredient per acre. For example, for powdery mildew, the new product label lists a 3-3.5 fl oz rate as opposed to the 1.5-2 oz rate on the old product label. This represents a doubling of the amount of active ingredient for powdery mildew control by the new product. For Botrytis, the old 3 oz rate is now 3.8 fl oz, and for black rot, the old 2 oz rate is now almost doubled on the new label to 3.5-3.8 fl oz. Well, what does this mean then in practical terms for grape growers in the northeast? It could mean better disease control with the new product. However, if you already have powdery mildew resistance to the strobilurins in your vineyard, then increasing the amount of active ingredient probably won’t boost efficacy against that disease, and relying on the new formulation for powdery mildew control is risky. The same goes for Botrytis control, as strobilurin resistance among Botrytis isolates becomes more common. For black rot, it could represent improved control of that disease. However, I thought the 2 oz black rot rate for the old material was pretty effective already, and to my knowledge, there have been no cases of black rot resistance to the strobilurins (though I’m not aware anyone has been looking for it). And yes, it is registered for use in New York.

That’s what new. This next section borrows from Wayne Wilcox’ fungicide updates from last year. I have updated that information with new information from some of our research trials as well.

Fracture. According to Wayne’s insights last year, “Fracture is a product whose active ingredient is a fragment of a naturally occurring plant protein, and which has been registered for use on grapes for a couple of years. It has a 4-hr REI and a 1-day PHI, and the residue of its active ingredient is exempt from tolerance by the US-EPA (i. e., it is considered safe enough to humans that there is no limit on the allowable residue level in/on food products)”. We’ve now tested it for powdery mildew control over two years in Concord and Chambourcin and consider its activity against that disease to be modest. New York trial results appear similar. Trial results for bunch rot control I think are a bit more promising; we got fair to good control of bunch rot on Vignoles with this product last year (as good as a standard Botrytis fungicide program), and we’re looking forward to testing it again for that purpose this season. New York trials with Fracture have also shown control of Botrytis as good as standard materials, as well as some activity against sour rot. Fracture is expensive but may appeal to growers looking to reduce reliance on synthetic fungicides for bunch rot control, especially if used in combination with strict sanitation and cultural controls like leaf removal. We’re hoping to look at Fracture again this season, in combination with pre-bloom mechanized leaf removal, for integrated bunch rot control on Vignoles.

Polyoxin D zinc salt. Polyoxin D zinc salt (PZS) is a relatively new fungicide active ingredient with very low mammalian toxicity that has been classified by the U.S. Environmental Protection Agency (USEPA) as a “biochemical-like” pesticide. It degrades rapidly in the environment with a soil half-life of 2-3 days. Production of PZS occurs through a fermentation process using the soil bacterium Streptomyces cacaoi var. asoensis. The active ingredient inhibits chitin synthase, an enzyme essential for the production of chitin, an important component of fungal cell walls. The product is being sold as Tovano and OSO5%SC and is marketed through Certis USA. Over the past two seasons, our results with OSO on Concord and Chambourcin grapes have shown good to modest efficacy against powdery mildew, but no practical level of activity against black rot. For powdery mildew efficacy on fruit, OSO, at the 13 fl oz rate, was equal to or better than BadgeX2 (fixed copper), and equal to a standard rotational program of Quintec/Vivando/Toledo. As with most of the biopesticide type fungicides, cost per application is generally going to be higher than that of the standard synthetic fungicides.

LifeGard. LifeGard is another biopesticide approved for use on grapes in all states. It has provided really good results for the control of downy mildew in New York trials. Our past two years of testing in PA were a bust due to very dry conditions and little to no downy mildew up here in Erie County, PA. However, maybe we’ll get a good test of this product this year. LifeGard works by triggering a plants’ natural defense mechanisms against pathogens so the product may perform best after the vine has been ‘primed’ by an initial spray a few days before it is challenged with the pathogen. The label states that “initial triggering of plant defense response occurs within minutes of application, but 3-5 days are required to attain maximum level of protection”. This may be the reason our greenhouse inoculation trials with LifeGard were largely unsuccessful; we applied the pathogen just a few hours after application of the material instead of allowing ample time for the vine’s natural defense mechanisms to build up. Grapevines do not generally tend to respond to efforts to induce resistance, but the results from New York trials are encouraging and testing should continue.

There are several products also worth mentioning that have recently been made available to New York (and hence all) grape growers. Here is a brief recap of those materials.

  • Luna Experience: a combination product consisting of two unrelated active ingredients, tebuconazole, (a very familiar sterol-inhibitor (FRAC 3)) and fluopyram, a newer SDHI (FRAC 7). Luna Experience is labeled for powdery mildew control at 6.0–8.6 fl oz/A, and for Botrytis and black rot control at 8.0 – 8.6 fl oz/A. Trials in New York have obtained excellent control of powdery mildew with the 6 fl oz rate. For Botrytis, New York trials suggest the 6 fl oz rate works well from bloom through bunch closure but the 8 fl oz rate would be best by veraison or later, especially if there is any pressure. The higher rate is also recommended for black rot control for the first few weeks after bloom when berries are most susceptible. The fluopyram provides most of the powdery mildew control and all of the Botrytis control, while the tebuconazole provides most of the black rot activity. For resistance management, limit the number of applications of FRAC 7 materials (SDHIs) to two per season.
  • Zampro: We tested Zampro a number of years ago and found it to be an excellent material for downy mildew control. More extensive New York trials have gotten similar results. Though it has been approved for use in New York, it still cannot be used on Long Island. Zampro is another combination product of dimethomorph (FRAC 40, same as mandipropamid in Revus) and a new chemistry, ametoctradin.
  • Rhyme: The active ingredient in Rhyme is flutriafol (sterol inhibitor, FRAC 3) and extensive powdery mildew trials in New York have shown more consistent results at the 5 fl oz rate rather than the 4 fl oz rate: Rhyme was a little better than Rally (myclobutanil) and tebuconazole, about equal to Mettle (tetraconazole), but not as good as difenoconazole (the newer, more potent sterol inhibitor in Revus Top, Inspire Super, Quadris Top). It received a registration a couple years ago and is also available for use in New York as well (except for Long Island). Rhyme has excellent activity against black rot.
  • Topguard EQ: A combination product of flutriafol (just discussed above) and azoxystrobin (the ai in Abound). Obviously, this can’t be used in Erie County, PA, but is available to New York grape growers (except Long Island). The azoxystrobin picks up downy mildew (and Phomopsis?) that the flutriafol won’t, unless of course there is a significant presence of strobilurin resistant isolates of the downy mildew pathogen in your vineyard. For powdery mildew, the azoxystrobin adds a second mode of action against that disease, unless (once again) there is a significant presence of strobilurin resistant isolates of the powdery mildew pathogen in your vineyard. So, if you’re farming grapes in areas where sterol inhibitors and strobilurins have been used for many years and downy/powdery mildew resistance is suspected/likely or known, this product may not provide adequate control of these two important diseases, especially on highly susceptible wine varieties. What this product will definitely control is black rot: the azoxystrobin has excellent protective activity and flutriafol has excellent post-infection activity against this disease.

And finally, what’s new in the pipeline?

Miravis Prime. Miravis Prime is a product with two active ingredients: a new SDHI called adepidyn (FRAC 7) and an older, unrelated active ingredient known as fludioxonil (FRAC 12). This product is not yet registered for use on grapes, but federal registration may occur later this year, which will make it available for growers in most states (New York will probably have to wait at least another year). Our tests with Miravis Prime have shown good to excellent activity on powdery mildew, Botrytis, and black rot. Adepidyn (Miravis) provided excellent control of black rot in our 2015 and 2016 trials on Concord and Niagara fruit. The fludioxonil component in Miravis Prime is an older Botrytis fungicide, (introduced about 25 years ago) that is also found in a registered product called Switch (for Botrytis control in grapes). Having two active ingredients for Botrytis control makes this product effective at controlling Botrytis bunch rot disease in wine grapes.

Part 2 of this blog post will be published next Friday, May 18, 2018.

Looking Back at the 2017 Growing Season

By Michela Centinari, Bryan Hed, Kathy Kelley, and Jody Timer

The 2017 growing season was a rewarding one for many Pennsylvania (PA) grape growers; crop quality and yields generally met or exceeded expectations. However, this season was not without its challenges. Before we start planning for next year, let’s review this past season and discuss the important issues and concerns PA growers faced in 2017. In November a link to a 10-minute Internet survey was sent via email to 110 members of a PA wine grape grower extension mailing list. The survey was designed to solicit their feedback with regards to the 2017 growing and harvest season. Fifty participants completed the survey* and their responses form the basis of this blog article. So that we have a complete accounting for growers throughout the Commonwealth, we encourage PA wine grape growers who may not have received the email to contact us (Michela Centinari; Bryan Hed) and provide their contact information so that they can be included in future surveys.

First, some information about participant demographics

Of those who provided the region where they grew grapes (44 participants), the majority (16) were located in the Southeast region, followed by South Central (9), Northwest (8), Northeast (5), North Central (3), and Southwest (3) regions.  Species of grapes survey participants grew are listed in Table 1.

Screenshot 2017-11-30 14.59.03

What did we ask the survey participants?

Participants were asked to indicate the average yield of the grapes they grew in 2017 by selecting the appropriate category: “poor,” “below average,” “average,” “above average,” or “record crop.” Although growers often adjust crop load to meet a desired level, environmental or other unexpected factors may cause final yield to differ from expected, “average” values.

Participants were also asked to rank the overall quality of the fruit from “poor” to “excellent,” and the insect and disease pressure from “below average” to “above average.”  Respondents were then directed to open-ended questions where they indicated what cultivars performed “below,” “average,” or “above average” and why.

Weather conditions during the growing season

A look at the weather conditions throughout the growing season can help to explain participants’ answers.  In Figures 1 and 2, we reported monthly, seasonal (April 1 through October 31) growing degree days (GDD; index of heat accumulation), and precipitation collected by weather stations (http://newa.cornell.edu/) at two locations: Lake Erie Regional Grape Research and Extension center (LERGREC) in North East (Erie County, northwestern PA) and in Reading (Berks County, southeast PA). We compared the 2017 data to the previous 18-year (1999-2016) average.

Screenshot 2017-11-30 15.00.21

We recognize that weather conditions might vary greatly from site to site, but some general trends were observed. For example, April GDDs were above-average in many regions of the Commonwealth. On the other hand, May was slightly cooler than the average in both the Southeast and Northwest (Figure 1). Additionally, below freezing temperatures were recorded during the early morning hours of May 8 and May 9 at the agricultural experiment station located near the Penn State main campus in State College. Some of the grape cultivars grown at this research farm, especially those that typically break bud early like Marquette and Concord, sustained crop loss due to frost damage. Fortunately, spring frost affected relatively few growers in PA and only two survey participants, one from the Southwest and another from the Northeast, reported reduced crop yield due to early May frost damage.

Growing degree day accumulations were slightly above the long-term average in June and July. However, August was noticeably cooler than the average in the Southeast and many other regions of the state, but not in Erie which remained warmer than average nearly all season (Figure 1). As the season came to a close, temperatures in September and especially October were warmer than average at both locations (Figure 1).

In most regions of the state, precipitation was abundant, particularly in June, July, and August (Figure 2 and Table 2). The one exception to this trend was in the far Northwest corner of the state where rainfall along the Lake Erie shore was well below average in July and August. September was relatively dry statewide, which was a big relief for many growers after facing a wet summer.  As the season came to an end, October saw a return to higher amounts of rainfall in some areas of the state.

Screenshot 2017-11-30 15.07.18

Survey participants’ responses 

Yield: Twenty-two respondents (44% of the participants) indicated that overall crop yield was “average,” which was close to the target values (Figure 3). Sixteen percent of the participants indicated that overall yield was “above average,” or “record crop,” while for 40% was “below average” or “poor.”

Screenshot 2017-11-30 15.01.39

“Poor” or “below average” yield was attributed to several factors, including poor or reduced fruit set, herbicide drift damage from a nearby field (for more information please refer to the newsletter article: Growth regulator herbicides negatively affect grapevine development) and/or disease issues (e.g., downy mildew, bunch rot). Two participants reported crop yield losses due to late spring freeze damage.  One respondent indicated that “above average” yield was likely related to bigger berry size.

Fruit quality: Participants were asked to rate fruit quality, with the majority of the respondents (82%) rating fruit quality as “average,” “above average” or “excellent.”  Only 18% of the respondents indicated that overall quality was “below average” or “poor,” although in some cases the rating varied depending on the cultivars grown as specified in a follow-up question.

Screenshot 2017-11-30 15.02.00

With the exception of the Northwest region, several participants across the state pointed out that despite the wet summer conditions the warm and dry fall weather favorably influenced fruit ripening, especially for late ripening cultivars.

For example, some of them commented:

  • Early cultivars were of lower quality than later cultivars due to the cold, wet weather in the August and early September time frame. The warm and dry later half of September and most of October benefited the later.”
  • Pinot Gris, Sauvignon Blanc, Viognier, Chardonnay all had excellent sugar levels and good pH and acidity. Flavors were well concentrated. Reds were average to good. Some like Merlot had low sugar levels while later varieties had better sugars like Cabernet franc and Cabernet sauvignon.  The late reds seemed to ripen more quickly than normal.”
  • “Later varieties were above average due to smaller crop size and better weather conditions.”

Disease pressure: Half of the growers who participated in the survey experienced “above average” disease pressure during the 2017 growing season, while 41% reported “average” disease pressure and only 9% reported that the disease pressure was “below average.” This contrasts markedly with results obtained in 2016 when 47% of survey participants experienced “below average” disease pressure (Looking back at the 2016 season).

Screenshot 2017-11-30 15.02.51

The major disease problem identified by the growers was downy mildew followed by bunch rot. A few respondents indicated that downy mildew pressure was particularly high in August. This is not surprising; downy mildew pressure is very dependent on rainfall and the threat of this disease would be particularly high in areas where recorded rainfall had been above average for most of the season (for example, Berks County).

It is important to note that areas of the state that experienced “above average” disease pressure may have a relatively high overwintering population of the pathogen(s), particularly if a fair amount of disease was actually observed in the vineyard. This can easily translate into higher disease pressure in 2018, especially if conditions remain wet.

In contrast to the majority of grape growing areas in PA, growers in the Lake Erie region experienced a second consecutive dry season, and disease development in many of the region’s vineyards was limited to powdery mildew in 2017. Therefore vineyards in the Lake Erie region will generally carry relatively low overwintering pathogen levels into 2018, with the exception of powdery mildew (a disease that is only dependent on rainfall for the first primary infections in early spring).

Despite the above-average wet conditions, respondents pointed out that fruit was clean from major diseases: “low fruit disease despite wet season,” and “given the weather conditions during the growing season overall our grapes were kept almost disease free.”

Several of them attributed their ability to keep disease pressure under control to a “persistent spray program,” “solid spray program and very good protective materials available,” and that “rainy season required that growers stay on top of their disease management program.  Botrytis, downy and powdery mildew could have been rampant.”

A respondent pointed out that in addition to a solid spray program new canopy management implemented likely helped to reduce Botrytis infection in susceptible varieties:  “I also started to leaf pull pre-bloom which I believe has loosened our clusters up and has allowed for better spray penetration and overall less rot.

Insect pressure: Twenty-two participants (45% of the respondents) experienced “average” insect pressure during the 2017 growing season, while 31% answered “above average” and 24 % “below average.”

Screenshot 2017-11-30 15.03.11

The majority of the growers who experienced “average” or “above average” insect pressure indicated problems with late-season insect pests, such as Spotted Wing Drosophila (SWD), wasps and hornets (for more information on those insect pests and how to manage them please refer to: Is Spotted Wing Drosophila a problem in my wine grapes?; Late season insect management)

Some of them commented:

SWD seems to be more present at the end of the season,” “Drosophila was the primary insect,” “SWD was above normal.”

Japanese Beetles were also named, although answers were divided: some respondents indicated “Japanese beetle pressure was lower than in previous years” while others answered that “Japanese beetles were the most prevalent insect” and they were “very aggressive in the vineyard.”  A respondent observed a new insect in the vineyard, the grape leafhopper.  Grapevines can tolerate fairly high populations of leaf hoppers and Japanese beetles without harm to the crop. Populations of fewer than 20 leafhopper nymphs/leaf usually does not require spraying (Japanese Beetle: A common pest in the vineyard).

In the Lake Erie region the grape berry moth was once again the most destructive insect present.  The unusually dry summer kept a potentially large population to average numbers.  Brown Marmorated stink bug damage is beginning to be noticeable in some Lake Erie vineyards (Will the Brown Marmorated stink bug be a problem in wine and juice?)

Unfortunately, the insect who made its big entry this season into southeastern PA vineyards was the Spotted Lanternfly (Lycorma delicatula).  Spotted Lanternfly (SLF) is an invasive insect first discovered in Berks County in 2014 and is now threatening parts of southeastern PA and Southern New York (Invasive insect confirmed in New York). Half of the respondents from the Southeast region (8 participants) observed the Spotted Lanternfly in their vineyards, and this was the first year for many of them.

Some of them commented:

  • At the end of the season I started seeing Spotted Lanternfly.”
  • “Lantern fly moved into my vineyard this year. Some of us believe honeydew from lantern fly is attracting yellow jackets and other bees, which were really bad.”
  • The Spotted Lanternfly in our vineyard continues to put pressure on the crop; we estimated that we killed 1/2 million adults in September.”
  • The significant increase in the adult Spotted Lantern Fly population this season in our area causes significant concern for our vineyard longevity. While many of the sprays were able to knock the populations back quickly only so many applications could be made. Within a few days of spraying and killing the adults, new adults migrated into the vineyards.”

The quarantined area for SLF at the beginning of the season included three counties of southeastern PA, but by the end of the season, SLF populations had decidedly increased causing the quarantine area to be markedly expanded.  The PA Department of Agriculture does not have the quarantine map completely updated at this time, however, they do have a search quarantine map where you can put in your location to check to see if you are included in the quarantine. (https://www.agriculture.pa.gov/spottedlanternfly; http://www.agriculture.pa.gov/plants_land_water/plantindustry/entomology/spotted_lanternfly/pages/default.aspx)

Information on SLF and measures that can be taken to stop its spread can be found at: https://extension.psu.edu/spotted-lanternfly, additional resources are listed on the Penn State Extension website. As stated in the article: “Penn State is at the forefront of education and research aimed at stopping the spread of this exotic species.” Penn State is seeking to hire an entomologist extension associate to coordinate outreach and response efforts for the SLF.

We are also planning to discuss Spotted Lanternfly management options at the Penn State Grape Disease & Insect Management Workshop, soon to be announced through the Penn State extension website and our listserv.

We would like to thank all the growers who participated in the survey. Their time spent responding to these questions provides us with valuable information that research and extension personnel can utilize to customize efforts to help the industry grow and improve. The more responses we receive, the more accurately our efforts can target the needs of our stakeholders statewide.  Despite some challenges, it was a rewarding growing season for many PA wine grape growers. We are looking forward to tasting this season’s wines!

Notes

* All procedures were approved by the Office of Research Protections at The Pennsylvania State University (University Park, PA). Upon completion of the survey, each participant was entered into a raffle to win one of three $25 gift certificates that could be redeemed toward any Penn State Extension wine or grape program fee.

 

 

 

 

Grapevine leafroll associated virus; A brief introduction to an old disease. Should Pennsylvania grape growers be concerned?

By: Bryan Hed, Michela Centinari, and Cristina Rosa

As if wine grape growers don’t have enough challenges in this day and age, the effects of grapevine viruses have been taking on greater importance in eastern vineyards over the past several years. Studies examining grapevine leafroll-associated viruses are developing a growing body of information that will be essential for vineyard managers to continue moving the eastern wine grape industry forward. Grape growers in the eastern United States need not feel they are the only ones with this disease management challenge (as is the case with many fungal diseases of grapes); grapevine leafroll-associated viruses (GLRaVs) are found in vineyards all over the world (Compendium of Grape Diseases). This group of viruses causes a disease known as grapevine leafroll disease, and the association of symptoms with grapevine leafroll viruses was recognized over 80 years ago. As is the case with so many plant pathogens, the worldwide distribution of these viruses occurred as a result of increased movement of plant material/goods across the globe; the ever widening dissemination of infected planting stock (Compendium of grape diseases). The effects of these leafroll viruses is most severe on – you guessed it – cultivars of V. vinifera, where the disease is known to greatly reduce yield, vine vegetative growth or vigor, and cold hardiness; a factor of critical importance for these cultivars grown in the northeastern United States. Grapevine leafroll disease can also delay fruit maturity, reduce color development in red grapes, and fruit quality (decreased soluble solids, increased titratable acidity) of V. vinifera grapes (Fuchs et al. 2009), which can negatively impact perceived wine quality. The severity of the effects of leafroll viruses is dependent on a great number of factors such as grapevine cultivar, virus strain, climate, soil, cultural practices, stress factors, etc. So naturally, the severity of symptoms can vary from one season to the next (Compendium of Grape Diseases). With respect to cultivar, the effects of these viruses on Vitis interspecific hybrids and Vitis labrusca are generally considered to be less serious, but are also less well defined and studied.

Infection by leafroll viruses results in the degeneration of primary phloem tissues in grapevine shoots, leaves and clusters (Compendium of Grape Diseases). As one can imagine, this can have profound effects on all parts of the vine. Symptoms of the disease, which are generally most observable on V. vinifera, consist of cupping and discoloration of older leaves in late summer and fall. On red fruited varieties, leaves of infected vines can display a distinct red coloration of the interveinal tissue, while veins remain green (Figure 1). On white fruited varieties of V. vinifera, symptoms are less striking and leaves tend to look yellowish (chlorotic) and cupped (Figure 2). Leaf discoloration generally affects older leaves first, but these symptoms are not diagnostic of the disease, as they may be due to other causes such as nutrient deficiencies, water stress, and even crown gall. Analysis of grapevine tissues in the laboratory is the only way to confirm the presence (or absence) of these viruses.

Figure 1. Grapevine Leafroll Disease on red fruited Vitis vinifera. The infected vine is on the left (Courtesy: Dr. Wendy McFadden, OMAFRA)

 

Figure 2. Symptoms of leafroll virus on white Vitis vinifera. Note the more subtle yellowing of the leaves and cupping of leaf margins. (Courtesy: Dr. Wendy McFadden, OMAFRA)

Currently, there are about seven GLRaVs found in cultivated grapes, the most common being GLRaV-3. These viruses are easily spread over long distances through the movement of infected nursery stock, but can be spread (vectored) within the vineyard by mealybugs (Compendium of Grape Diseases). Unfortunately, there are no known sources of resistance to GLRaVs among Vitis species and they have been found in many cultivated grape varieties, including V. labrusca, Vitis interspecific hybrids, and V. vinifera. Interest in grapevine leafroll disease and the extent of its effects has been growing in the eastern United States over the past ten years or so. Surveys conducted in New York, Ohio, and Virginia (Fuchs et al. 2009, Jones et al. 2015, Han et al. 2014), have provided confirmation of the presence of GLRaVs in commercial vineyards and have yielded important information necessary to the management of grapevine leafroll disease. For example, infection by GLRaVs is permanent and infected vines must be destroyed to reduce the incidence of grapevine leafroll disease. Therefore, management of the disease would naturally include planting only stock that is free of GLRaVs. Insecticides that target mealybugs and soft scales can prevent vine to vine spread (within the vineyard) of GLRaVs that are known to be vectored by these insects (Compendium of Grape Diseases). Indeed, studies have shown that applications of insecticides like dinotefuran (Scorpion) and spirotetramat (Movento) can significantly reduce mealybug counts and result in a slowing of the progress of the disease in vineyards. One study from New York (Fuchs et al. 2015) showed that insecticide applications should target overwintered and second instar mealybug crawlers from bud swell to bloom and summer generation crawlers later in mid-summer. A study with grape phylloxera as a potential vector of these viruses showed that phylloxera can acquire the virus through phloem feeding on infected vines, but there was no evidence that phylloxera can transmit it (Wistrom et al. 2017).

As was mentioned earlier, cultivars of Vitis labrusca (Concord, Niagara) can also become infected with GLRaVs, but the infections appear to remain latent or dormant (Bahder et al. 2012) and have not been shown to result in visual symptoms of the disease (Wilcox et al. 1998). On the other hand, cultivars of V. vinifera are severely affected by GLRaVs and make up a very important and growing sector of the PA wine grape industry. Surveys conducted in New York, Ohio, and Virginia (Fuchs et al. 2009, Jones et al. 2015, Han et al. 2014) have revealed the presence of GLRaVs in commercial vineyards to the north, west, and south of Pennsylvania and have led to the development of some important guidelines for management of grapevine leafroll disease.

Given the fact that grapevine leafroll disease is common worldwide and that grapevine leafroll disease can profoundly impact wine quality and grapevine health, researchers at Penn State University are initiating a project to look for GLRaVs in Pennsylvania vineyards.  As in other states, the study is targeted to help growers recognize the impact that the disease may be having on the Pennsylvania wine industry and help them to address the effects of these viruses on productivity and fruit quality, reduce their spread and impact, and thereby grow and improve the wine grape industry in Pennsylvania.

The short term, initial objectives of this project will focus on the development of an online survey to collect information from growers with regard to the presence of symptoms of grapevine leafroll disease in Pennsylvania vineyards and their interest in participating in the project. The project will then follow up with tissue sampling from participating, symptomatic and non-symptomatic vineyards throughout the state and serological analysis to determine the presence of Grapevine leafroll virus-1 and Grapevine leafroll virus-3 – the most common of the leafroll viruses – in commercial vineyards in Pennsylvania. The collection of vineyard samples across the state will map the incidence and geographical distribution of these viruses on cultivars of Vitis vinifera and Vitis interspecific hybrid grapevines. The project will also determine and compare the impact of grapevine cultivar and age on infection by Grapevine leafroll virus-1 and -3 in Pennsylvania. Once infected vines have been identified in Pennsylvania vineyards, future objectives will focus on studying the impacts of grapevine leafroll disease on grape quality and productivity in Pennsylvania, and management techniques to mitigate the economic impact of the disease on the Pennsylvania wine industry.

Vineyards will be selected from all parts of Pennsylvania, but the number of locations will favor northwestern and southeastern PA, where the majority of vineyards are located. The study will be expanded as new findings are made and the results will be made available to growers at various meetings throughout the next several years.

 

Literature cited:

Bahder, B., Alabi, O., Poojari, S., Walsh, D., and Naidu, R. 2013. A Survey for Grapevine Viruses in Washington State ‘Concord’ (Vitis x labruscana L.) Vineyards. Plant Health Progress, August 5, 2013. American Phytopathological Society (online).

Compendium of Grape Diseases, Disorders, and Pests. 2nd edition, 2015. Editors Wayne F. Wilcox, Walter D. Gubler, and Jerry K. Uyemoto. The American Phytopathological Society. Pp. 118-119.

Fuchs, M.Martinson, T. E.Loeb, G. M.Hoch, H. C. 2009. Survey for the three major leafroll disease-associated viruses in Finger Lakes vineyards in New York. Plant Disease 93:395-401.

Fuchs, M.Marsella-Herrick, P.Hesler, S.Martinson, T.Loeb, G. M. 2015. Seasonal pattern of virus acquisition by the grape mealybug, Pseudococcus maritimus, in a leafroll-diseased vineyard. Journal of Plant Pathology Vol.97 No.3 pp.503-510

Han, J.Ellis, M. A.Qu, F. 2014. First report of Grapevine leaf roll-associated virus-2 and –3 in Ohio vineyards. Plant Disease Vol.98 No.2 pp.284-285

Jones, T. J.Rayapati, N. A.Nita, M. 2015. Occurrence of Grapevine leafroll associated virus-2, -3 and Grapevine fleck virus in Virginia, U.S.A., and factors affecting virus infected vines. European Journal of Plant Pathology 142:209-222.

Wilcox, W. F.Jiang, Z. Y.Gonsalves, D. 1998. Leafroll virus is common in cultivated American grapevines in western New York. Plant Disease Vol.82 No.9 pp.1062.

Wistrom, C. M., G. K. Blaisdell, L. R. Wunderlich, M. Botton, Rodrigo P. P. Almeida & K. M. Daane. 2017. No evidence of transmission of grapevine leafroll-associated viruses by phylloxera (Daktulosphaira vitifoliae). European Journal of Plant Pathology. Volume 147, issue 4. pp 937–941.

Growth Regulator Herbicides Negatively Affect Grapevine Development: Identification of Herbicide Drift Damage, How to Prevent it, and What to do if it Occurs in your Vineyard

By: Michela Centinari

The Penn State Extension grape team has been receiving reports on herbicide drift damage in vineyards from a number of Pennsylvania wine grape growers this growing season, definitely many more than in previous years. All herbicides registered for grapes can potentially harm the vines if not applied in accordance to the pesticide label (e.g., glyphosate products) [1]. However, in many of the reported cases through the 2017 growing season the damage was caused by herbicides not registered for grapes, which drifted into the vineyards from nearby fields.

Damage from herbicide drift is, unfortunately, something that grape growers across the country are too familiar with. It represents an economic threat for the grape and wine industry and should not be underestimated. Herbicide drift damage can, indeed, result in significant crop losses which may extend to multiple seasons, and in some cases it also results in vine death. Several extension web resources are available to assist grape growers in preventing and dealing with herbicide drift damage. Some of them are listed at the end of this article, including one from Andy Muza, extension educator at Penn State (Growth Regulator Herbicides and Grapes Don’t Mix).

Due to the increase in reports of herbicide drift damage in Pennsylvania vineyards it seems appropriate to discuss some key points surrounding this issue. This article will review how to identify herbicide drift symptoms, what measures grape growers and pesticide applicators can take to prevent herbicide drift, and what steps to take if the drift occurs.

Plant growth regulators (PGR) herbicides are those most likely to injure grapevines, mainly through drift.

I will only focus on the herbicides which belong to the plant growth regulators (PGR) mode of action group. Common active ingredients of PGR herbicides are 2,4-D (2,4-Dichlorophenoxyacetic acid; phenoxy family), dicamba (benzoic acid), tricolopyr or picloram (pyridine family). A partial list of common PGR herbicides as well as other herbicides that may injure grapevines can be found at Preventing Herbicide Drift and Injury to Grapes, Table 1.

PGR herbicides are widely used for controlling broadleaf weeds in many crops, such as wheat, corn, soybean, pasture, rangeland, etc. They are also frequently utilized to control unwanted broadleaf vegetation in turf, by railroads, road ditches, fence lines, and rights-of-way. These herbicides are not registered for use with grapes. However, when applied to a nearby field, they can drift into the vineyard and cause significant injury to grapevines.

Most of the herbicide drift damage reported this season by Pennsylvania grape growers were caused by drift of PGR herbicides (Figure 1). Physiological symptoms to PGR exposure is not too surprising because grapevines are extremely sensitive to PGR herbicides, including the phenoxy, benzoic, and pyridine classes of compounds [2]. For example, herbicides containing 2,4-D can damage grapes at a concentration 100 times lower than the recommended label rate. Moreover, drift from PGR herbicides can injure grapevines located half a mile or more from the application site.

Figure 1. 2,4-D damage on Grüner Veltliner in Pennsylvania. The leaves are severely distorted, the shoot tip died, and bloom failed.

What is “drift”?

Drift is defined as “the movement of herbicides off the site where they were applied” [3]. Non-target drift can occur either as spray drift or vapor drift. Spray drift occurs during herbicide application when small droplets move off the application site under unfavorable wind conditions. Vapor drift occurs after herbicide application as the spray material volatizes or evaporates and is carried away from the application site by wind or temperature inversions. Some PGR herbicides, such as ester formulations of 2,4-D, readily volatilize, especially when used under high temperatures and low humidity conditions (high vapor pressure) [3].

How PGR damage occurs in grapevines

PGR herbicides mimic auxins, plant hormones that regulate growth and development. Applications of PGR herbicides disrupt plant hormone balance causing growth abnormalities. PGR herbicides can be absorbed by both roots and leaves, however grapevines are usually injured through foliar absorption.

How to tell if the vines have been damaged by PGR herbicide drift

Damage from PGR herbicides typically appears within 2 days of the drift occurrence. Herbicide drift can damage leaves, shoots, flowers, and fruit. Leaf symptoms are often easy to recognize, but sometimes can be mistaken with those of fanleaf degeneration, a viral disease [3]. Growers can send pictures of damaged vines to a local extension specialist for confirmation.

Typical symptoms include:

  • Distorted leaf appearance: Symptoms are typically more severe on the youngest leaves and shoot tips. Affected leaves are “smaller, narrow, deformed, and they have closely packed, thick veins that lack of chlorophyll” [4]. They may also have a distinct fan-shape appearance, and depending on the herbicide’s active ingredient, they can bend downward or cup upward (Figures 2, 3). Leaves may or may not outgrow the symptoms, it largely depends on the severity of the injury and other factors listed in the following section (“Factors affecting the severity of injury”). It is also common to see regrowth of deformed leaves after drift exposure [3].

Figure 2. Leaf cupping caused by improper application of Stinger (PGR-herbicide). Photo credit: Rob Crassweller.

Figure 3. 2,4-D injury on leaves. Photo on the left: A. Muza, Penn State.

  • Shoot growth: Damaged shoot tips rarely resume growth, but lateral shoots can keep growing giving in some cases a “bushy” appearance to the vine resulting in a highly shaded canopy and poor fruit sun exposure.
  • Flower clusters (inflorescences): symptoms can include aborted or failed flowers, and poor fruit set (Figure 4). If the injury is severe enough it can cause reduced yield at harvest and poor fruit quality, in addition to potentially illegal residues of herbicide on the exposed crop.

Figure 4. 2,4-D herbicide drift damage on Grüner Veltliner flower clusters. Photo taken on July 19, 2017 approximately two months after the herbicide drift incident. Notice only two berries developed properly (circled in the photo).

In some cases, depending on the timing and level of drift exposure, floral symptoms may be much more pronounced than those on the leaves making the diagnosis more difficult (i.e., growers may relate poor fruit set or dead flowers to other causes rather than herbicide drift) (Figure 5).

Figure 5. 2,4-D herbicide drift damage on Riesling flower clusters. Photo taken on June 26, 2017. Notice the leaves around the clusters look healthy.

If the damage occurs early in the season, between bud burst and bloom, as it usually does, a significant reduction in healthy leaf area during the period of rapid shoot growth may affect vine photosynthetic capacity, lowering vine ability to fully ripen the crop and possibly its ability to survive cold winters.

Unfortunately there is no guarantee that the vines will fully and rapidly recover from herbicide drift damage. Carry-over effects into the following years, such as reduction in vine vigor, yield, fruit quality, and increased susceptibility to diseases, are common if the damage is extensive and/or the vines have been repeatedly exposed to PGR-herbicide drift. Finally, vines may die as a consequence of their weakened condition [2].

What factors affect the severity of PGR-herbicide drift damage?

Some of the most important factors affecting the severity of drift damage are:

  • Vine growth stage at the time of exposure. Grapevines are always sensitive to PGR herbicides, but they are most susceptible during the early part of the growing season, from bud burst through bloom. While dependent on the growing season and site, in Pennsylvania this usually occurs around April through June. Early in the growing season shoots are rapidly growing and PGR herbicides are quickly translocated to the shoot tip, where the natural concentration of auxins is greatest inside the grapevine. If exposure occurs later in the season, vines typically outgrow the damage and still produce good yield [5].
  • Vine age: Younger plants are more vulnerable and they have a lower ability to recover from the PGR herbicide damage than mature vines. Young vines may be killed even at low exposures [6].
  • Level of exposure: Higher concentration and/or repeated exposures will result in higher disruption of the vine’s physiology and lower ability of the vines to rapidly and fully recover from the damage [3].
  • Grapevine variety. All grapevine varieties are sensitive to PGR herbicides, but some may show more visual and physiological symptoms than others (see for example Table 1, Questions and Answers about Vineyard Injury from Herbicide Drift)
  • Other factors include herbicide concentration and formulation (for example ester formulations of 2,4-D are more volatile than amine formulations, thus ester formulations of 2,4-D are more prone to move off-target as vapor), weather conditions (temperature, humidity, and most importantly wind speed) at the time of herbicide application.

What is the best strategy to protect vines from herbicide drift injury?

Prevention is undoubtedly the best strategy for grapevine growers to avoid herbicide damage. To reduce the risk of herbicide drifting into their vineyard, vineyard managers and/or owners should be proactive. Some prevention steps both grape growers and nearby growers of other crops can take are listed below:

  • Maintain good relations with neighbors. Vineyard owners and managers should make sure their neighbors within approximately a half-mile to 1 mile radius, are aware that vines are extremely sensitive to PGR herbicides [3]. It is also recommended to encourage neighbors to “use drift-reduction spray nozzles (nozzles that produce large droplets) and to select herbicides that are less likely to injure grapes” [3]. If growers of other crops are unaware of damage to grapevines, collecting information such as this blog post, may be an important educational tool to share. Mike White, viticulture extension specialist at Iowa State University, suggests to share an aerial map of the property showing the vine­yard location with neighbors and commercial pesticide applicators to increase their awareness. It is also recommended to communicate the presence of the vineyard to state and county highway departments.
  • Windbreak (shrubs, trees, physical barriers) and a buffer area between the vineyard and the edge of the field being sprayed are always a good idea. Penn State offers a free publication or pdf print-out regarding windbreaks: http://extension.psu.edu/publications/uh172/view
  • For those states where the service is available, growers can register the location of their vineyard on https://driftwatch.org/. This online service is not available in Pennsylvania, but in many Midwestern states growers and pesticide applica­tors can use this web resource free of charge to report (growers) and locate (applicators) potential drift hazards.

Taking all these steps may not guarantee that herbicide drift will not occur in your vineyard, but increasing pesticide applicators awareness of grape sensitivity to PGR herbicides, the resulting economic loss, and potential litigation risks may very well serve the purpose.

Applicators should always follow all the measures available to minimize the risk of herbicide drift into a nearby vineyard or to other sensitive crops. Legal complaints may result in expensive settlements. In an extreme example, an owner of a 150-acre vineyard in Australia was awarded AUS$ 7M in damages over pesticide drift (Grape grower Awarded $7M in damages over spraying) that occurred from 2013 to 2015.

If PGR herbicides are applied after vine bud burst, applicators should consider eliminating volatile compounds and apply only non-volatile products.

Extension personnel could also facilitate communication between grape and crop field growers as it happens in Long Island, NY. Extension personnel from Cornell University-Long Island, including Alice Wise and Andy Senesac, organized a meeting with local grape and sod growers to tackle the herbicide drift issue which was affecting local grape growers without having to resort to regulatory restrictions. The result of that meeting was a ‘gentleman’s agreement’ not to spray herbicides containing 2,4-D after April 15, around bud burst for the earliest grapevine varieties in Long Island. To keep all parties informed, extension sends out a weekly reminder about this issue.

What to do if the drift occur

Here some key steps Mike White put together on what to do right after a drift incident [7]:

  1. Identify area affected.
  2. Document the date, time and growth stage of the grapes.
  3. If possible, identify the source of the drift and make a determination if you want to settle the problem amongst your neighbors.
  4. Contact your state department of agriculture (Pennsylvania Department of Agriculture, PDA) as soon as possible if you cannot determine the source of the drift and/or you want to formalize the complaint (30 – 45 day deadline in many states).
  5. Flag both affected and unaffected plants, take high reso­lution pictures weekly until symptoms subside and measure final yields per plant.
  6. Severe injury settlements should be delayed until after next season’s harvest. Photo and yield documentation should be continued. Unless the settlement offered seems exceptionally lucrative, I would suggest delaying any settlements until after next season’s harvest to assess for potential carry-over vine damage.

For information on where to find a drift consultant please refer to Need Help? Pesticide Drift Consultants

How to estimate the loss in revenue

Tim Martinson, viticulture extension specialist at Cornell University, provided useful examples on how to estimate the economic loss associated with herbicide drift damage under different scenarios. Scenarios include vine recovery across multiple years, with and without the need of vines replacement. Please refer to: Diagnosis, Economics, Management of Grape Injury from 2,4D and other Growth Regulator Herbicides.

How to manage damaged vines

There is limited information available on best management practices for vines affected by herbicide drift damage. To favor a full and a rapid recovery it is recommended to still implement  good management practices and avoid further stress to damaged vines, as for example over cropping (assuming damaged vines have fruit). Fungicide applications made to protect the fruit should not be necessary if the fruit has been removed [8]. It is also recommended to adjust pruning strategies to smaller vines, with the intent of regaining full vine size [9].

 

Resources

  1. Growth regulator herbicides and grapes don’t mix. Penn State. https://psuwineandgrapes.wordpress.com/2015/10/16/growth-regulator-herbicides-and-grapes-dont-mix/
  2. Watch out for: Grapes. Purdue University. DW-10-W. https://www.extension.purdue.edu/extmedia/ho/dw-10-w.pdf
  3. Preventing herbicide drift and injury to grapes. Oregon State University. EM 8860. http://extension.oregonstate.edu/yamhill/sites/default/files/spray_drift/documents/3-preventing_herbicide_drift_to_grapes_osu_8660.pdf
  4. Avoid phenoxy herbicide damage to grapevines. Texas Cooperative Extension. http://winegrapes.tamu.edu/files/2015/11/phenoxy1.pdf
  5. Avoiding 2,4-D injury to grapevines. Colorado State University. http://webdoc.agsci.colostate.edu/cepep/FactSheets/Avoiding%202,4-D%20Injury%20to%20Grapevines.pdf
  6. Questions and answers about vineyard injury from herbicide drift. Kansas State University. MF-2588. https://www.bookstore.ksre.ksu.edu/pubs/MF2588.pdf
  7. Need Help? Pesticide drift consultant. Northern Grapes Project. http://northerngrapesproject.org/wp-content/uploads/2013/01/11-3-NE-Find-Drift-Consultant.pdf
  8. Top 10 questions about herbicide drift into vineyards. Iowa State University. https://www.extension.iastate.edu/wine/growersnews/243-may-29-2013#Top
  9. The view from New York: Diagnosis, economics, management of grape injury from2,4‐D and other growth regulator herbicides. Northern Grapes Project. http://northerngrapesproject.org/wp-content/uploads/2013/01/Martinson-2-4D-Presentation.pdf

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.