Experimental and registered soft-chemistry fungicides were tested in various combinations for the control of powdery mildew in a 44 yr-old Chardonnay grape vineyard in the Sacramento-San Joaquin River Delta in California. Fungicides were mixed in a 25or 50 gal Nifty-Fifty pump tank/engine spray system (Rears Mfg. Co., 2140 Prairie Road, Eugene, OR 97402) and applied with hand-gun sprayers at 150-200 psi. In each trial, two-vine plots were arranged in a completely randomized design with 5 replicatesper treatment. Individual treatments were applied during the period from 14 Apr until 11 Jul. Spray volumes were gradually increased from 100 to 250 gal water/A as the shoots grew. Leaves near the clusters on the north and south side of the vines were removed on 21 May and 3 Jun to provide better air circulation and fungicide coverage. Twenty five random clusters from each plot were evaluated. Disease incidence (percentage of infected sampled clusters per plot) and severity (percentage of infected berries per sampled cluster) were assessed on 21 Jul.
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