Miticide Efficacy Trial, 1990

Abstract

Abstract This experiment was conducted in a furrow-irrigated corn field at the Southwest Research-Extension Center. Treatments were arranged in a randomized complete block design with 4 replications. Plots were 4 rows wide (10 ft), 50 ft long with a 10 ft border of untreated corn on each side and a 10 ft alley between plots. Prior to treatment, 2 plants in each of the 2 center rows of each plot were flagged. The natural field population of spider mites was very high and reasonably well distributed so no artificial infestation was necessary. Pretreatment counts were made on 26 Jul by visually searching one-half of every other leaf (one-quarter plant) on the flagged plants for large (adult female) mites. All treatments were applied on 27 Jul, except for the experimental pesticidal soap which was applied on 31 Jul. Most of the treatments were applied with a high clearance sprayer using a 10 ft boom with 3 nozzles directed at each row (1 nozzle directly over the row and 1 on each side of the row on 18-in drop hoses). The sprayer was calibrated to deliver 20 gal/acre using a ground speed of 2.4 mph and 30 psi. Thio-Sul was applied with a high clearance sprayer calibrated to deliver the equivalent of a 0.2 inch irrigation on the 2 center rows (5227 gal/acre) using 3 Delavan 100/140, .75-inch rain drop nozzles. The experimental pesticidal soap used in this test was produced at Kansas State University. Counts were made on 2 and 15 Aug (6 and 19 DAT) by searching one-half of every other leaf on the flagged plants. Mite counts were converted to mites per plant for analyses and presentation. Efficacy was evaluated by comparing the mean number of mites per plant among treatments using SAS Proc ANOVA and by comparing pretreatment means with posttreatment means using the Henderson and Tilton formula. The spider mite species composition which was present during the test was evaluated by collecting several mites from the flagged plants in each plot with a vacuum sampler and mounting them on glass slides for microscopic examination.