Evaluation of fungicide programs for control of grapevine powdery mildew in a commercial Chardonnay vineyard, 2007

摘要

The experiment was conducted in a vineyard of Umbrella-Kniffin-trained, mature grapevines located at Dresden, NY. QoI fungicides provided very poor control of powdery mildew in this vineyard in 2002 and 2003; laboratory tests of sampled isolates confirmed the presence of a G143A mutation in the cytochrom b allele, conferring a high degree of resistance to these materials. Treatments in 2007 were applied to 4-vine plots arranged in a randomized complete block design and replicated 5 times. Elite 45WP(4.0 oz/A), Dithane Rainshield 75DF (4.0 lb/A) and Yellow Jacket 90 Wettable Sulfur II (3.0 lb/A) were applied to all plots on 29 May, prior to the initiation of the experiment. Variable treatment sprays were applied with a hooded-boom sprayer at 300 psi(2069 kPa) in a volume of 50 gpa (467 l/ha) prebloom (spray #1) and 100 gpa (935 l/ha) subsequently. In addition to the treatment sprays, the following materials (rate/A) were applied to all plots (including checks) on the indicated dates, to control downy mildew, black rot and Japanese beetle: Dithane Rainshield 75DF (4.0 lb) on 8 Jun; Dithane Rainshield 75DF (4.0 lb) and ProPhyt (4.0 pt) on 22 Jun; ProPhyt (4.0 pt) and Danitol 2.4 EC (1 pt) on 9 Jul, 17 Jul, 1 Aug and 14 Aug. Disease assessments weremade on 25 clusters and on 25 leaves from the center of each plot on 17 Sep. Disease incidence was calculated as the percentage of leaves or clusters showing any infection; disease severity (area diseased) was rated using the Barratt-Horsfall scale andconverted to percentage values using Elanco conversion tables. Rainfall amounts measured at Geneva, NY (approx.10 mi away) were 1.58, 1.61, 2.62, 1.50 and 2.96 in for May, Jun, Jul, Aug and Sep respectively.