Efficacy of Miticides Against Corn Spider Mites, 1985

Abstract

Abstract This experiment was conducted in furrow-irrigated corn planted at the Garden City Experiment Station in Finney County, KS. Fifteen treatments and a check were arranged in a randomized complete block design with 4 replications. The plots were 4 rows wide (10 ft) and 50 ft long with a 10-ft border at the end of each plot. Most miticide treatments were applied with a high clearance sprayer using a 10-ft boom extending over 4 rows. Three hollow cone nozzles were directed at each row (1 nozzle directly over the row and 1 on each side of the row on 18-inch drop hoses). The sprayer was calibrated to deliver 20 gal of water with 30 psi of CO2 pressure. One treatment was applied using three 3/4 inch rain drop nozzles mounted on the high clearance sprayer at tassel height between the rows to simulate a chemigation application. This system was calibrated to deliver 5430 gal of water with 20 psi. The treatments were applied on 12 Aug. Mite counts were made by visually searching the leaves on 1 side of 8 flagged plants in each plot for larger mites (mostly adult females). These plants had previously been infested (1 to 2 wk pretreatment) with mites, 4 plants with TSSM from a newly established greenhouse colony, and 4 plants with Banks grass mites from an infested corn field. Pre-treatment counts were made 1-6 Aug and posttreatment counts were made 21-27 Aug. Mite samples were collected with a vacuum sampler from each of the 2 groups of flagged plants in each plot. Forty mites from each sample were selected at random and mounted for microscopic examination and species determination. The percent TSSM in each sample was then calculated. This test was designed to test these miticides against both the Banks grass mite and the TSSM; however, the plots were found to contain predominantly TSSM when the posttreatment counts were made. Therefore, the counts from all 8 plants in each plot were combined for analysis. Grain yields were determined by hand harvesting 40 row-ft from the 2 center rows in each plot 1-4 Sep. All yields were corrected to 15.5% moisture.