Evaluation of Cultural Practices and Fungicides for Managing Phytophthora Fruit Rot of Watermelon, 2006

Authors: Kousik, Chandrasekar - Shaker; HASSELL, RICHARD - CLEMSON UNIVERSITY

Submitted to: Plant Disease Management Reports
Publication Type: Research Notes
Publication Acceptance Date: 2/7/2007
Publication Date: 3/14/2007
Citation: Kousik, C.S., Hassell, R. 2007. Evaluation of Cultural Practices and Fungicides for Managing Phytophthora Fruit Rot of Watermelon, 2006. Plant Disease Management Reports. 1:V010.

Interpretive Summary:

Technical Abstract: The experiment was conducted at the US Vegetable Laboratory farms in Charleston, SC. The soil was Yonges loamy fine sand. The fields were sprayed with Sandea (1 oz/A) prior to planting for managing weeds. Four week old seedlings of a susceptible watermelon cultivar “Mickey Lee” grown in 50-cell jiffy trays were transplanted on 12 Jun 06 onto raised beds with 40-in centers. Bed to bed spacing was 14.2 feet. Beds were either bare or covered with white plastic mulch. Plants were irrigated as needed using drip irrigation. There were 4 replications per treatment with one row of 12 plants per plot. Plants were spaced 18-in. apart within rows. There was 11-ft spacing between each plot on the bed. Fungicide treatments were applied using a CO2 backpack sprayer equipped with 4-nozzle (Flat fan, Teejet 8002VS) spaced 19-in apart on a hand held boom (4.8 feet long) calibrated to deliver 31 gal/A. The first application was made on 21 Jul when the watermelon fruit were about 6-inches in diameter. Subsequent applications of all fungicide treatments were made every week on 28 Jul, 4, 11 and 18 Aug for a total of five applications. Plots were inoculated on 27 Jul and 10 Aug by scattering a mixture of mefenoxam sensitive and insensitive isolates that were grown on wheat grains soaked in V8 juice. The isolates were grown individually and mixed prior to spreading them in the field. Total fruit and number of rotted fruits per plot were recorded on 23 Aug and used to calculate fruit rot incidence. Data from only three replications were recorded for the bare ground plots because of significant weed pressure which resulted in poor plant growth across treatments in one replication. Because of significant weed pressure, plots were sprayed twice post planting with the herbicide Poast (1.5 pt/A) and once with Sandea (1 oz/A). Total rainfall of 5.61-inches was recorded during the growing season. Total rainfall from start of fungicide treatments to data recording (33 days) was 1.87-inches with 23 mild rainy days and the average daytime temperature was 82oF. Abundant sporulation was observed on the rotting fruit. There were no significant interaction between the cultural practices and fungicide treatments with respect to fruit rot incidence (P=0.9384). However, significant differences among the treatments was observed (P=0.0008). Several of the fungicide treatments significantly reduced fruit rot compared to the untreated check. Though numerically lower, Ridomil Gold/Copper and Ranman treatments were not significantly different from the check. The two treatments that contained Revus (mandipropamid) significantly reduced fruit rot compared to the untreated check. Similarly Captan 80 WDG treatments were also effective in reducing fruit rot. No phytotoxicity to fruit or foliage was observed for any of the fungicide treatments.