Evaluation of select fungicides and fungicide programs for managing downy mildew of cucumber, 2018

摘要

The experiment was conducted at the Pennsylvania State University Russell E. Larson Agricultural Research Center, Pennsylvania Furnace, PA. The field was plowed and fertilizer (N-P-K; 11-52-0 at 145 lb/A and 46-0-0 at 130 lb/A based on soil test results) was broadcast and incorporated on 15 and 18 May. Nineteen raised beds with 1.5-mil black-plastic mulch and a single row of drip-irrigation tape were formed in early Jun. Raised beds were 48-in. wide and 6-in. high and were laid on 9-ft centers. For each set of three rows, the center row was an untreated guard row and the two outer rows were treatment rows. On 7 Jun, cvs. Darlington (susceptible) and DMR 264 were direct seeded, two seeds per hole, spaced 24-in. apart, one row per bed in designated treatment plots. Guard rows were directed seeded with cv. Straight Eight. Plots were single rows, 16-ft long and separated by 8-ft bare plastic buffer. Fungicide treatments were replicated four times and arranged in a split-plot randomized complete block design with cultivar as the whole-plot and fungicide treatment as the sub-plot. Plots were thinned to one plant per hole or missing plants replaced with transplants in late Jun so that each plot consisted of six plants. Cucumber beetles were managed withan application of Admire 2F applied with a Solo backpack sprayer (mixed 5 ml/lgal then drench applied 5.0 fl oz/plant) on 14 Jun and Baythroid (2.8 fl oz/A) was applied on 10 Aug. Weeds were managed with an application of Profine 75DF (1 oz/A) plus Prefar (6 qt/A) on 29 May that was activated with 0.5 in. of overhead irrigation on 1 Jun. On 6 Jun, Round-up (1.5 pt/A) was applied between the plastic and supplemental hand weeding was conducted throughout the season. Plots were fertigated regularly (N-P-K;20-20-20 at 7 lb/A) and at increasing intervals as the crop matured. Fungicide applications were made using a tractor mounted, R&D C02 powered offset-boom sprayer traveling 2 mph and calibrated to deliver 42 gal/A at 32 psi at the tank through six TX-18hollow-cone nozzles on 20-in. centers on 16 and 26 Jul, 6, 15 and 23 Aug for a total of five applications. Natural inoculum was relied upon and symptoms were first observed on 8 Aug. Downy mildew severity was rated on a continuous scale of 0 to 100% based on the percentage of the leaf surface showing symptoms across the whole plot on 9, 16, 19 and 26 Aug and then used to calculate the area under the disease progress curve. Rainfall totals (in.) were 4.49, 10.20 and 6.84 for 7 to 30 Jun, Jul, and 1 to 26 Aug, respectively.