Grapes come in many disease-resistant cultivars, but this does not mean they are all impervious to diseases. Even resistant varieties can develop grape diseases under the proper conditions. Sprays designed for grape diseases can prevent infection and eradicate existing diseases quickly to avert crop disasters. Use them only as directed, as the ingredients may lead to food toxicity if misused.
Copper fungicide sprays are highly effective at controlling downy mildew and other molds on leaves of grape vines, according to the Ohio State University Extension. When copper fungicides are applied early in the growing season, they protect the plants from developing mildews and molds on plants and, later, on fruits. Copper fungicides can be effective preventative agents even for highly susceptible cultivars.
Liquid Lime Sulfur
Liquid lime sulfur can be used to prevent or halt the spread of phomopsis fruit rot. Often confused with black rot, phomopsis turns berries a light brown color close to harvest time, then black spores break through the skin and the fruit shrivels. An application of liquid lime sulfur while the vines are dormant can help control this disease. Liquid lime sulfur also helps ward off anthracnose infections when used in conjunction with copper fungicides, according to the University of Massachusetts Extension.
Bordeaux spray is a fungicide designed to ward off powdery mildew and other fungal infections. It also fights blights and keeps insects away. It can be purchased in gardening stores, but many people prefer the homemade variety, combining copper sulfate, often called bluestone, and very finely-ground lime in water. Before it is used, the solution is strained through a cheesecloth, then applied to the grape vines. This solution is often used during the dormant season to supplement growing season actions; the proportions of chemicals to water vary based on the season of application.