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Minimizing Spray Programs for Control of Grape Disease Based on Phenological Stages of Susceptibility 1998

Project Leader: Wayne Wilcox

Objectives:

1. Determine the optimum timing and minimum number of sprays to reliably control black rot.

2. Determine whether two fungicide sprays, applied immediately before bloom and 2 weeks later, can provide acceptable commercial control of powdery mildew on 'Concord' fruit if good spray coverage is obtained.

3. Determine whether applications of the foliar fertilizer monopotassium phosphate (MKP) and a traditional fungicide (a DMI or Abound, if anticipated registration of the latter is forthcoming) can provide acceptable control of powdery mildew on a highly susceptible grape cultivar by targeting the traditional fungicide solely during the period of maximum fruit susceptibility.

Results:

Effective control of powdery mildew fruit infections can be obtained with just two targeted sprays, but effective control of leaf infections requires additional applications thereafter. MKP was a potentially viable substitute for traditional fungicides in these later sprays, although traditional materials were somewhat more effective. Control of black rot was also obtained when sprays were restricted to the immediate prebloom and early postbloom periods. Separate experiments indicated that berries were no longer susceptible to infection from midsummer onwards, obviating the need for fungicidal protection during that time.