Evaluation of fungicide programs for control of early leaf spot and stem rot on spanish-type peanuts, 2014

摘要

The trial was conducted at the Caddo Research Station near Ft. Cobb, OK in a field containing a Binger fine sandy loam soil previously cropped to peanuts. Granular fertilizer (18-46-0 lb/A N-P-K) and the herbicide Glyphos 4S at 1 qt/A were applied prior to planting on 13 May using strip-till techniques. The herbicides Prowl H2O 3.8S at 1 pt/A + Valor 51WDG at 2 oz/A + Glyphos 4S at 1 qt/A were applied pre-emergence immediately after planting. Post-emergence herbicide applications included Clethodem 2E at 16 fl oz on 10 Jun, Cadre 4F at 4 fl oz + Butyrac 200 at 1 pt/A on 1 Jul, and Select 2E at 1 pt/A on 22 Aug and 4 Sep. Plots consisted of four 25-ft-long rows spaced 36 in. apart. The experimental design was a randomized complete block with four blocks separated by a 5-ft-wide fallow buffer. All data were taken from the two center rows. Fungicide applications made on 14-day calendar schedule beginning 7 Jul. Fungicides were broadcast through flat-fan nozzles (8002vk) spaced 18 in. apart with a CO2-pressurized wheelbarrow sprayer. The sprayer was calibrated to deliver 22 gal/A at 40 psi. Plots were inoculated with S. rolfsii by sprinkling 70 ml/plot of infested oat kernels along the two center rows of each plot on 7 Aug. Rainfall totaled 5.43 in. for Jun, 2.22 in. for Jul, 1.46 in. for Aug, 1.29 in. for Sep., and 2.05 in. for Oct. Plots received 15 applications of sprinkler irrigation at 0.5 to 1 inch per application that totaled 13 in. of water. Leaf spot was assessed by estimating the percentageof leaflets with leaf spot (including defoliated leaflets) and the percentage of leaflets defoliated in three areas per plot on 9 Oct. Stem rot was assessed by counting the number of 6-in. row segments with symptoms on 9 Oct. The counts were converted to the percentage of row length affected. Plots were dug and inverted on 17 Oct, windrowed for 5 days, and harvested with a combine equipped with a sacker. Pods were dried and cleaned prior to taking weights. Data were analyzed using the GLM procedure ofSAS 9.3 and means were separated by Fisher's Least Significant Difference Test where indicated by a significant (P=0.05) treatment effect.