Suppression of Sorghum Midge, 1988

Abstract

Abstract Two organophosphate and 2 pyrethroid insecticides were evaluated for sorghum midge control at the Texas Agricultural Experiment Station Research Farm near College Station. Grain sorghum was planted 5 May on rows spaced 40 inches apart. Sixteen rows of mixed hybrid sorghum of varying maturity ranges were planted 2 wk before adjacent to the test plots to increase sorghum midge abundance within the test plots during the flowering period. Treatments were compared in 8-row by 75-ft-long plots arranged in a randomized complete block design with 4 replicates. Applications were made with a self-propelled, high-clearance sprayer to all rows using TX-6 hollow-cone nozzles at 40 psi with a spray volume of 8 gal/acre. Insecticide applications were begun when 20-25% of the panicles were flowering. Treatments were applied 2, 6, and 10 Jul. Because of a rainfall that occurred 10 Jul during the spray operations the last application of Dyfonate was made 11 Jul. Karate plots received only 2 applications, on 2 and 6 Jul. Rainfall of 0.90, 0.45, and 1.33 inches occurred 4, 10, and 12 Jul, respectively, and may have influenced the outcome of the study. Data on ovipositing adult midge density, kernel damage, and grain yield were collected from the middle 6 rows of each plot. Adult sorghum midge abundance was determined just prior to each application and consisted of enclosing 10 individual sorghum panicles/plot with clear plastic bags. Panicles were subseqeuntly excised and returned to the laboratory for examination and counting of adult midges. Visual estimates of the percentage of midge damage were made by 4 independent observers on 8 Aug, with each observer estimating the percentage damage to 5 panicles/plot. Panicles were hand-harvested from 2 randomly selected 13-ft sections of row/plot and mechanically threshed.