Efficacy of fungicides for managing cucurbit powdery mildew and treatment impact on pathogen sensitivity to fungicides, 2008

摘要

The primary objective of this study was to evaluate the efficacy of several individual fungicides and fungicide alternations for the control of cucurbit powdery mildew. Both new and currently registered products were tested in an area where in previous years strainsof the pathogen with QoI resistance and moderate DMI resistance were detected before fungicide use. The field experiment was conducted at the Long Island Horticultural Research and Extension Center on Haven loam soil. The field was plowed on 10 May and tilled on 11 Jun. Seeds were planted at approximately 24-in. plant spacing within rows with a vacuum seeder on 20 Jun. The planter applied fertilizer in a band about 2 in. away from the seed. A blend of controlled release fertilizers, consisting of 300 lb/A 15-18-12 and 100 lb/A ESN, was used. The herbicides Strategy (3 pt/A) and Sandea (0.5 oz/A) were applied over the entire plot areas on 22 Jun followed by 0.5 inches of overhead irrigation used for activation. During the season, subsequent weeds were controlled by cultivating, roto-tilling between plots, and hand weeding as needed. Red clover at 10 lb/A was planted with a grain drill to establish driveways on 12 Jul. Cucumber beetles weremanaged by applying the insecticide Admire 2 F (20 fl oz/A) in a narrow band over the planted rows immediately after the herbicide application on 22 Jun and applying Asana XL (9.6 fl oz/A) to foliage on 31 Jul, 14 Aug, and 21 Aug. To manage damping-off,RidomilGold EC (1 pt/A) was broadcast over the field and incorporated mechanically on 10 Jun. A soil penetrant to increase water penetration, SprayHandler (0.5 pt/A), was applied with Ridomil. The following fungicides were applied to foliage preventively for downy mildew(Pseudoperonospora cubensis) and Phytophthora blight (Phytophthora capsici): Ranman 400 SC (2.75 fl oz/A) on 20 Jul, 14 Aug, 21 Aug, 30 Aug, and 21 Sep; Forum 4.16SC (6 oz/A) on 5 Aug, 12 Sep, and 24 Sep; and Curzate 60 DF (3.2 oz/A) on 31 Jul. Kocide 3000 (1-1.25lb/A) was applied for bacterial leaf spot on 5 Aug and 12 Sep. Plots were three 15-ft rows spaced 68 in apart. The plots were 18 ft apart. A randomized complete block design with four replications was used. Plots were inspected for powdery mildew symptoms weeklybeginning on 22 Jul. Initially 50 older leaves were examined per plot. The examined leaves were selected from the oldest third of the foliage based on leaf physiological appearance and position in the canopy. On 30 Jul the IPM threshold of one affected leaf out of 50 oldleaves (Plant Dis. 80:910-916) was found to have been reached in most plots (50 of 64). Treatments were started on 30 Jul with subsequent applications made weekly on 5, 13, 19, and 27 Aug, 5 Sep, and 11 Sep using a tractor-mounted boom sprayer equipped with D5-25 hollow cone nozzles spaced 17 in. apart that delivered 96 gal/A at 100 psi. Additional powdery mildew assessments were made on 4, 11, 18, and26 Aug; 2 Sep and 13 Sep on upper and lower leaf surfaces. Starting on 11 Aug, fewer than 50 leaves were examined in plots with a high percentage of symptomatic leaves. Mid-aged leaves were also assessed beginning on 18 Aug and young leaves on 28 Aug. Five leaves ofeach age group were rated starting on 2 Sep. Mid-aged to young leaves were examined on 13 Sep, as most old leaves had senesced then. Powdery mildew colonies were counted; severity was assessed by visual estimation of percent leaf area infected when colonies could notbe counted accurately because they had coalesced and/or were too numerous. Average severity for the entire canopy was calculated from the individual leaf assessments. A square root transformation was used when needed prior to analysis to achieve homogeneity of variance.Canopy condition including defoliation was assessed on 29 Aug and 12 Sep. Fruit quality was evaluated in terms of handle (peduncle) condition for mature fruit without rot on 30 Sep, 8 Oct, and 23 Oct. Handles were considered good if they were green, sol