Fungicide efficacy for control of grape powdery mildew, 2008.

摘要

Fungicide treatments were arranged in a randomized complete block design in a block of ‘Pinot Noir’ planted in 1985 on a 7 ft x10 ft wide spacing. Vines were trained to a bilateral cordon with spur pruning. Vines were pruned from 27 to29 Feb to approximately 40 shoots/vine. Each treatment was replicated on 4 sets of 5 vines. Treatments were applied approximately every 14 days using a hooded boom sprayer at 150 psi for the first 4 applications, and 200 psi for the remaining 3 applications. The rate of water used was 96 gal/A for the first 2 applications, 115 gal/A for the 3rd application, 147 gal/A for the 4th application, and 162 gal/A for all subsequent applications. Approximately 2.5 to 5.4 gal of spray suspension was used per 20 vines depending on time of year. Fungicides were applied on 30 May (6 inch shoots), 12 Jun (EL 12), 25 Jun (EL 15), 10 Jul (EL 29), 24 Jul (EL 33), 7 Aug (Bunch close), and 21 Aug (start of Veraison). Canes were cut above the top wire on 17 Jul and maintained at this height throughout the growing season. No fertilizer was applied this year. No leaves were removed from the fruiting zone. According to the Gubler-Thomas powdery mildew forecasting model, therewere 2 rain events between bud-break and end of bloom that were favorable for ascospore release and infection: 1 moderate infection period (2 Jun), and 1 low infection period (5 Jun). The risk index climbed above 60 in late June and remained highthroughout the summer (with only one day below 60) until mid Sep. Incidence and severity of powdery mildew on leaves were evaluated on 3 Jul (incidence only), 16 Jul, 31 Jul, 13 Aug, and 28 Aug. Incidence and severity of powdery mildew onclusters were evaluated on 18 Jul, 1 Aug, 15 Aug, and 28 Aug. Powdery mildew disease data were collected by randomly examining 50 leaves or clusters from the middle 3 vines of each replicate. Comparisons among treatments for severity ofpowdery mildew on leaves and clusters were evaluated by calculating the area under disease progress curves (AUDPC). AUDPC was calculated by multiplying the mean severity from two observation dates by the number of days betweenobservations (sigma[Yi+1 + Yi)/2][Xi+1-Xi] where Yi is severity of mildew at ith observation and Xi is the day of the ith observations). Values calculated between each pair of observations are added together to obtain a total AUDPC.