Effective management of northern grape diseases

by Luke Tubia
Planting season is here and for vineyard owners that means preparing to battle diseases that can destroy grape crops. To help growers understand these threats and how to manage them, Grape Pathology Specialist Dr. Wayne Wilcox and Pesticide Application Technology Specialist Dr. Andrew Landers of the Cornell Cooperative Extension hosted Effective Management of Northern Grape Diseases, a webinar explaining the most common grape diseases and treatments, as well as how to properly select and operate backpack pesticide sprayers.
Dr. Wilcox began the webinar with a list of the most common diseases affecting grapes in New York State. These diseases include Phomopsis, anthracnose, downy mildew, powdery mildew and black rot.
Phomopsis, which is produced early in the season, is most commonly identified by an infection of the shoots of the plant and is more serious in Concord and Niagara grapes. Wilcox said this infection worsens with long, rainy periods; he suggests pruning out the dead wood and spraying with a pesticide.
Anthracnose can look similar to Phomopsis, but with lesions on shoot a lot deeper and with distinctive blackened lesions on the fruit. Wilcox said proper canopy management and a treatment of lime sulfur in the late dormant stage should help to control anthracnose.
Powdery and downy mildew appear as fuzzy white spores on the leaves of the plant and can rot fruit and leaves right off. Downy mildew can actually get into grapes and rot them from the inside, but Wilcox said taking care of your canopy and using most Group II fungicides like copper, captan and mancozeb can control this problem. Powdery mildew is different because it only grows fungus on the outside layer of leaves and can be taken care of with organic pesticides such as potassium salts.
Black rot gets into the fruit and rots and shrivels the grapes. This infection usually happens during warm rains when spores produced in rotten berries spread to new clusters. Wilcox says to prune out your mummies and begin a fungicide program from bloom through four-plus weeks.
Of course applying these pesticides takes some skill and knowledge of equipment. Pesticide Application Technology Specialist Dr. Andrew Landers says knowing how to properly spray your crop is paramount. He suggests if using a backpack sprayer to use colored water instead of pesticide, and practice spraying over the white side of a sheet of wallpaper or even in the snow. This will help develop your spraying technique and ensure your entire crop is covered.
Landers also shared some tips for growers who use backpack sprayers. First, he says to make sure you don’t buy a cheap sprayer – anything under $150 should be considered inferior. Second, make sure your sprayer has at least three filters, including a basket filter, lance filter and nozzle filter. These filters keep your spray nozzle from clogging and wasting your time out in the field.
To limit loss of coverage from drift, Landers says to use a finer spray quality for insecticides and fungicides, a medium quality for herbicides where the leaves are your target and a coarse spray for soil applications of herbicides.
For more detailed instructions on choosing a spray quality and calibrating any sprayer for your needs, Dr. Landers has a series of instructional videos available by visiting Youtube.com and searching “nozzle selection Cornell.”
Every grower has to fight the endless battle of vineyard pests, but with a little help, your grapes can grow healthy and vibrant.
For more information on managing northern grape diseases, you can visit the Cornell University website and search: “insect and disease management.”
Happy growing!