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Minimizing Sprays for Grape Diseases

Need for chemical management decreases as new information about pest biology is uncovered

A project examining reduced spray schedules and the substitution of a foliar fertilizer for conventional pesticides brought to light new information about the grape diseases black rot and powdery mildew this year.

photo of healthy grapes

Black Rot. Plant pathologist Wayne Wilcox, of Geneva, found that grapes are most susceptible to black rot during a relatively brief period from the start of bloom until shortly after fruit are set (mid-to-late June through early July in upstate New York). They lose all susceptibility within a few weeks after that. Accordingly, he found that if three protective sprays were administered from bloom through mid-July, all later sprays were superfluous. While results from one year are an insufficient basis for a firm conclusion, the results do provide the basis for hope that sprays for black rot can be reduced by two or three applications per season.

Powdery Mildew. As was the case with black rot, Wilcox found that the most critical sprays for protecting grape berries against powdery mildew were those applied from bloom through fruit set. Although later fungicide sprays can still be beneficial (particularly for the grape foliage), they appear to be much less critical and might be replaced with alternative control practices.

Substituting Fertilizer. Monopotassium phosphate, a fertilizer that is applied to plant leaves, was applied to vineyard test plots in midsummer as a substitute for standard fungicide sprays. When integrated into a program using conventional fungicides in the critical fruit-set period beforehand, the fertilizer applications were as effective as standard spray materials thereafter.

Should implementation of these new practices become a reality following more data gathering, unnecessary sprays will be eliminated from the environment and growers' costs for materials, equipment, and labor will be lowered.