Submitted to: Plant Disease Management Reports
Publication Type: Research Notes
Publication Acceptance Date: 5/30/2009
Publication Date: 8/18/2009
Citation: Kousik, C.S. 2009. Evaluation of Cultural Practices and Fungicides for Managing Phytophthora Fruit Rot of Watermelon, 2008. Plant Disease Management Reports. 3:V133. Interpretive Summary:
Technical Abstract: The experiment was conducted to evaluate the efficacy of new fungicides to manage Phytophthora fruit rot of watermelon. The soil at the experimental field in Charleston, SC, was Yonges loamy fine sand. The field was sprayed with Roundup Pro (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 the cultural treatments (bare ground or plastic mulch) and subplots were the 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 and 21-ft between beds. 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. Fungicide treatments 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 the watermelon 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 grown separately 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 on 2 Sep and used to calculate fruit rot incidence. Percent fruit rot data from the plots were transformed to arcsine values and analyzed by ANOVA and means were separated using the lsmeans, stderr/pdiff procedure of SAS (P=0.05). There were no significant interaction between the cultural practices and fungicide treatments with respect to fruit rot incidence (P=0.9486). Similarly there was no significant difference between the two cultural treatments (P=0.9263). However, significant differences among the fungicide treatments was observed (P=0.0001). Significant fruit rot incidence was observed in the untreated check plots and all the fruits were rotted in some replications. Several fungicide treatments significantly reduced fruit rot compared to the untreated check. Though fruit rot incidence was numerically lower, for Ridomil Gold/Copper treatments, they were not significantly different from the check in the cultural treatments. In this trial Captan 80 WDG was not as effective as observed in previous years most likely because of one less application. However, the Captan 80 WDG + Kocide 54DF treatment significantly (P=0.0001) lowered fruit rot compared to untreated check. The two treatments that contained Revus 250SC significantly reduced fruit rot compared to the untreated check. Similarly Presidio 4L was also effective in reducing fruit rot. No phytotoxicity to fruit or foliage was observed for any of the fungicide treatments.