Published on April 25, 2022

Updated on April 16, 2024

Contents:

• Focus on Phomopsis, Black Rot, Downy Mildew… and Anthracnose
• Be Protected Prior to an Extended Wet Period
• Thoughts on Early Protective Fungicide Applications

Focus on Phomopsis, Black Rot, Downy Mildew… and Anthracnose

All four of the above causal agents above have similar environmental requirements to cause disease. First, rainfall is needed to dislodge spores. Second, grapevine tissue needs to be wet from rainfall, dew or even heavy fog for infection to occur. Third the incidence of infection is dependent of air temperature and as air temperature increases the incidence of infection increases. In general, if air temperatures are between 60 to 75° F and grapevine tissue remains wet for 8 to 10 hours then an infection period is evident.

Black Rot

Managing black rot begins during the dormant pruning season. Black rot overwinters as mummy berries, infected rachises, and lesions on infected canes. At a minimum, all rachises and rachises with mummy berries and infected canes should be pruned out and removed from the vineyard (Figure 3). If you are behind on pruning this season, then prioritize and at a minimum drop last season’s rachises onto the ground. Black rot spores will have a difficult time fighting gravity to infect new shoot growth. However, leaving infected rachises and mummy berries on the vine significantly shortens the distance spores need to travel to cause infection and besides gravity is on the spore’s side now.

Even though Black rot spore load is reduced by removing overwintering spores, the crop still needs to be protected. Early vegetative grape growth can be protected with mancozeb containing fungicide products. If your cultivar is susceptible to Black rot and most cultivars grown in Missouri are except Norton that is only slightly susceptible, plan a spray program to get you through 4 to 5 weeks post bloom. By 4 to 5 weeks post bloom the berries have developed age related resistance to black rot.

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Be Protected Prior to an Extended Wet Period

The current forecast is predicting an extended wet period for this week. If your grapevines are at half-inch shoots or beyond, make sure a protective fungicide has been applied.

• If you have not applied a protective fungicide and you have ½-inch or longer shoots then apply a cover application of a protective fungicide prior to a rainfall event
• If you have applied a protective fungicide within the last six days and two or more inches of rain has occurred since the application then reapply a protective fungicide
• If your previous protectant fungicide application was 7 days ago or longer and 1-inch of rain fell after application then reapply a protective fungicide

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Thoughts on Early Protective Fungicide Applications

A cool wet spring often results in many growers sharpening their pencils to adjust protective spray schedules to balance fungicide products with seasonal maximum limits. Some growers avoid seasonal maximum limits by not applying early season protective sprays. I cannot understand why some growers do not apply protective sprays in the early season but most often the explanation is that there is very little growth to intercept the spray. Certainly, that is true, the early season growth intercepts very little of the spray being applied. However, if a protectant fungicide is not applied prior to an infection period then disease development is almost assured.

There are ways to become more sustainable with these early season fungicide applications. Depending on your sprayer type set it up so the spray is directed to the cordon and developing shoots. For airblast type sprayers this means turning off most nozzles not directed at the cordons and developing shoots. Also turn down the fan speed. If your set-up limits you from adjusting your PTO speed then look into reducing air input using a plywood donut. Air intact may also be adjusted on some sprayers by adjusting fan blade pitch. For sprayers equipped with hydraulic fans the fan speed should be adjusted down for early season fungicide applications. Reduced fan speed during the early season will result in better pesticide deposition on the target tissue. Lastly, sustainability can be further enhanced by using a recycling sprayer that catches overspray and recirculates the spray back into the tank. Some recirculating sprayer manufactures claim up to 35% savings in pesticide costs.

If you want to learn more about sustainable vineyard spraying, look into reading Andrew Landers book entitled “Effective Vineyard Spraying”.

How Much Protection Remains?

One of the biggest frustrations of very early season disease management in grapes is not knowing how much fungicide protection remains after a period of time passes. After an application the clock starts ticking and a number of factors degrade the fungicide. The three main factors causing degradation are UV light, rainfall, and biological degradation by microorganisms. Pesticide labels provide some insight on how many days a fungicide should provide protection before another application should be made. One of the major issues grape growers run into in the early spring are extended rainfall events that may often last days. These weather events can cause limitations on getting another cover spray applied. Are there other options to lengthen the protection cover period.

Two options, the first option is to apply a systemic fungicide prior to the extended rainy period and the second option is to apply some biological for disease management. From experience we know that using systemic fungicides will provide extended protection compared to most protectant fungicides. One of the major drawbacks of using these systemic products early in the season is that it limits further use of the product as the season progresses.

We need to consider resistance management and limiting the selection pressure on specific fungal organisms. Additionally, systemic fungicides cost more per application than protectant fungicides. In the last few years, biologicals have been introduced to the fungicide market that have some value in providing protection for certain grape pathogens. These products are not stand-alone products, meaning the biologicals need to be integrated into disease protection plan that includes other fungicides. The one product that has shown promise is Life-Gard. LifeGard is Bacillus mycoides isolate J that upon application results in systemic acquired resistance in the grapevine tissue. The LifeGard WG label lists both phomopsis and black rot as targets. Michigan research has reported good activity on phomopsis cane and leaf spot and black rot as reported by Wendy Mcfaddensmith in ONfruit (see references below). Research in Kentucky evaluated LifeGard incorporated into a traditional spray program compared to a traditional spray program and untreated control for the management of black rot. The traditional spray program + LifeGard was not significantly different compared to the traditional spray program for yield and cluster grade 1 (0 to 33% damage from black rot). Another treatment compared in this research was a traditional spray program + LifeGard with three treatments removed during week 5, 9 and 13. This reduced spray program (5 treatments) had similar yield and grade 1 fruit quality compared to the traditional spray program (8 treatments) and the traditional spray program + LifeGard (8 treatments). This one-year trial suggests that LifeGard may provide an opportunity to reduce fungicide application frequency. A caveat, this research was on Chambourcin and other cultivars may respond differently.

As an aside. I believe one of the first fungicides approved for grapes that results in systemic acquired resistance was Regalia. Regalia contains the active ingredient from Giant knotweed Reynoutria sachalinensis. According to the Regalia label, there is no activity on phomopsis or black rot. It bears repeating that these fungicides are not stand-alone and need to be incorporated into an IPM program.

In summary, at present science has not provided the opportunity to know in real-time how much of a protective fungicide exists on the grapevine. So, your best management is to rely on information of your pesticide label, knowing the amount of growth the vines have experienced since your last fungicide application, and the weather events your last fungicide application has had to endure. There are a number of biofungicides on the market for grapes, the current problem is little efficacy data exists from multiple locations. There is an extreme need to generate more data on these biofungicides, especially state or regional data. As more data is generated there may be some upside potential for the grape growing industry such as improved sustainability by reducing the number of fungicide applications. There is a growing need to evaluate these products especially in in light of the potential loss of traditional chemical derived synthetic fungicides.

References

Otoguro, M. and S. Suzucki. 2018. Status and future of disease protection and grape berry quality alteration by micro-organisms in viticulture. Applied Microbiology. https://sfamjournals.onlinelibrary.wiley.com/doi/10.1111/lam.13033

Mairs, R.A. 2018. Effects of Bacillus Mycoides Supplement in a Reduced Frequency Fungicide Program on Chambourcin Grapevines (Vitis Vinifera L.). Western Kentucky University Master The-sis. https://digitalcommons.wku.edu/cgi/viewcontent.cgi?article=4049&context=theses

Mcfaddensmith, W. 2020. New biological tools for disease management in grapes. ON-fruit Information for Ontario Fruit Growers. July 13, 2020. https://

Please scout your vineyards on a regularly scheduled basis in an effort to manage problem pests. This report contains information on scouting reports from specific locations and may not reflect pest problems in your vineyard. If you would like more information on IPM in grapes, please contact Dean Volenberg at 573-882-0476 or 573-473-0374 (mobile) or volenbergd@missouri.edu

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