Chemical Control of Sorghum Midge on Grain Sorghum, 1986

Abstract

Abstract 2.2 acres of grain sorghum were planted 15 May on rows spaced 40 inches apart. Twelve rows of mixed hybrid sorghums of varying maturity ranges were planted prior and adjacent to the test plot site to increase midge populations. Nine insecticide treatments and an untreated check were compared in a randomized block design with 4 replications. Experimental plots were 8 rows wide and 45 ft long, but only the middle 4 rows were sprayed. Applications were made with a high-clearance, self-propelled sprayer using TX-3 hollow cone nozzles and calibrated to deliver 5.9 GPA at 42 psi and 3 mph. Insecticide applications began when 30-40% of the panicles were flowering and when average adult midge density was 2.5 midges/panicle. Treatments were applied 11, 15 and 19 Jul. The first application was made under slightly adverse wind conditions (10-15 mph gusts). 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 per replication. On the 2 subsequent sampling days, 5 panicles were sampled from each treatment plot. Visual estimates of percent midge damaged spikelets were made by 6 independent observers, with each observer rating 10 randomly selected panicles/plot. Panicles were hand harvested from one 20-ft section of treated row per plot. The harvested sorghum panicles were threshed and the grain was weighed. Data were analyzed by conventional analysis of variance and multiple comparison procedures.