Evaluation of cultural practices and fungicides for managing Phytophthora fruit rot of watermelon, 2008

摘要

The experiment was conducted at the US Vegetable Laboratory farm in Charleston, SC. The soil was Yonges loamy fine sand. The field has been infested with Phytophthora capsici for the past two years. The field was sprayed with RoundupPro (1 pt/A) and Strategy (2 pt/A) after bedding but prior to planting for weed management. The experimental design was a split-plot with treatments arranged in a randomized complete block and replicated 4 times. Main plots were culturaltreatments (bare ground or plastic mulch) and subplots were fungicide treatments. Four-week-old seedlings of a susceptible watermelon cultivar Mickey Lee grown in 50-cell jiffy trays were transplanted on 19 Jun onto raised beds with 40-in centers.Beds were spaced 21-ft apart. Beds were either bare or covered with silver plastic mulch. Plots were a single row of 12 plants spaced 18-in. apart with 15-ft spacing between plots. Plants were irrigated as needed using drip irrigation. Fungicidetreatments were applied using a CO2 backpack sprayer equipped with 4-nozzles (flat fan, Teejet 8002VS) spaced 19-in apart on a hand held boom (4.8 ft long) calibrated to deliver 31 gal/A. The first application was made on 5 Aug when most of thewatermelon fruit were about 6-7 inches in diameter. Subsequent applications of all fungicide treatments were made weekly on 15, 21, and 27 Aug for a total of four applications. Mefenoxam sensitive and insensitive isolates of P. capsici were grownseparately on rice grains soaked in V8 juice in mason jars. Plots were inoculated with a mixture of isolates by scattering equal amounts of infested rice grains in the plots on 26 Aug. Total fruit and number of rotted fruits per plot were recorded on2 Sep and used to calculate fruit rot incidence. Bird damage was observed on fruits in several plots and such fruits were not considered in the analysis. Percent fruit rot data from the plots were transformed to arcsine values, analyzed by ANOVA andmeans were separated using the lsmeans, stderr/pdiff procedure of SAS (P=0.05). Slight injury due to Strategy was noticed during early stages of plant growth, however, the plants recovered well to produce fruit. Weeds between beds were controlledduring the season with spot application of Roundup. Total rainfall of 16.56-inches was recorded during the growing season (34 rainy days). Total rainfall from start of fungicide treatments to data recording (27 days) was 6.12-inches with 12 rainydays.