Insecticides for Suppression of Sorghum Midge on Dryland Grain Sorghum, 1987

Grain sorghum (1.8 acres) was planted 19 May on rows spaced 40 inches apart. Twelve rows of mixed-hybrid sorghums of varying maturity ranges were planted prior to and adjacent to the test plot to increase abundance of sorghum midge during anthesis of sorghum panicles in the test plots. Five insecticide treatments and an untreated check were compared in a randomized block design with 4 replications. Experimental plots were 8 rows wide and 80 ft long. Applications were made to the middle 6 rows with a high-clearance self-propelled sprayer. Insecticide applications began when 30-40% of the panicles were flowering and when average adult midge density was 0.7 midges/panicle. Treatments were applied 24 and 30 Jul and 4 Aug. Adult midge density was determined 1 day prior to application of insecticide treatments. Sampling consisted of securing and collecting individual sorghum panicles in plastic bags. Samples were examined in the laboratory and midges were counted. Prior to the first insecticide application, midge density was determined from sampling 25 randomly selected panicles/replication. On the 2 subsequent sampling days, 5 panicles were sampled from each treatment plot. Visual estimates of the percentage of midge-damaged spikelets were made by 4 independent observers, with each observer rating 10 randomly selected panicles/plot. Panicles were hand harvested from 2, 2-m sections of treated row/plot. The harvested sorghum panicles were threshed, and the grain was weighed. Data were analyzed by conventional analysis of variance and multiple comparison procedures.