Evaluation of fungicides applied in alternation with Bravo for control of powdery mildew on watermelon

摘要

The experiment was done at the Clemson University Coastal Research and Education Center in Charleston, SC. The soil type was Yonges loamy fine sand with a pH of 7.0. The field was fallow in 2012 and was planted to rye and crimson clover in winter 2012-2013. In spring 2013, the field was disked twice. On 12 Mar, raised beds were shaped 3 ft wide on 6-ft centers, and 500 lb/A 10-10-10 fertilizer was banded within the row. Raised beds were formed, sprayed with the herbicide Dual Magnum at 1.3 pt/A, andthen covered with black polyethylene mulch. Alleys were sprayed with Prowl H2O at 2.1 pt/A and Strategy at 6 pt/A on 3 May. Watermelon was transplanted into every other row on 13 May in plots arranged as a randomized complete block design with four replications. Plots were 50 ft long with plants spaced 3 ft apart within rows. Between watermelon plots within rows, five plants of an acorn squash (Cucurbita pepo cv. Table Ace) susceptible to powdery mildew were transplanted 3 ft apart to provide a source of inoculum. Mites and insects were managed by applications of Acramite (0.75 lb/A) on 23 May, Agrimek (3.5 fl oz/A) on 30 May, and Venom (4 oz/A) on 5 Jun. Ranman (2.75 fl oz/A) and Previcur Flex (1.2 pt/A) were applied to control downy mildew on 18 and25 Jun respectively. Liquid 8-0-8 fertilizer was applied to the field throughout the season through the drip irrigation system. Fungicide treatments were applied seven times with a CO2-backpack sprayer calibrated to deliver 74 gpa volume at 60 psi with a36-in. boom and three TeeJet TX 26 nozzles spaced 18 in. apart. Powdery mildew severity on leaves in field plots was rated on 25 Jun and 16 Jul. Additional observations were made on 5 Jul and 1 Aug. On 16 Jul, five leaves were selected randomly from each plot, and the top and bottom of each leaf were rated separately for powdery mildew severity. Average max/min temperatures for May, Jun, and Jul were 79.3 / 61.0, 86.2 / 71.2, and 85.9 / 73 °F, respectively. Max temperatures in each month were 2 to 4°F lower than the 50-yr normal. Rainfall for May, Jun, and Jul was 1.95, 14.24, and 2.81 in., respectively. Rainfall was less than the 50-yr normal for May and Jul and 2.4 times greater in Jun.