Insecticide Efficacy Against Second Generation Corn Borers, 1986

Abstract

Abstract This experiment was conducted in sprinkler-irrigated corn in Finney county, KS. Treatments were arranged in a randomized complete block design with 4 replications. The plots were 4 rows wide × 10 ft and 50 ft long. There were 2 sets of untreated check plots per replicate. The standard insecticide applications were made with a high clearance sprayer using a 10 ft boom with 3 nozzles directed at each row (one nozzle directly over the row and 2 suspended on 18 inch drop hoses). The sprayer was calibrated to deliver 20 gpa with 30 psi of CO2 pressure. The simulated chemigation applications were made using 3 Delvan 100/140, 0.75 inch rain drop nozzles mounted >n the high clearance sprayer at tassel height between the rows. This system was calibrated to deliver 47 gal in 2.4 min for each plot (5430 gpa). This application was equivalent to a 0.2 inch irrigation on the 2 middle rows. For the high volume applications, the chemicals were added to 200 gal of water in the main tank of the sprayer and agitated by recirculation. Treatments were applied on 28 and 29 Jul. The timing of applications was based on the Kansas State University European corn borer model and the presence of corn borer eggs in the field. Corn borer evaluations were made in late Aug by dissecting 10 corn plants in each plot (5 consecutive corn plants in each of the center 2 rows). The number of plants infested with each species of corn borer was recorded. Corn borer and stalk rot were evaluated in late Sep by dissecting 20 plants in each plot (10 consecutive corn plants in each of the 2 center rows). Stalk rot was rated using a scale of 0 to 3; 0—no visible stalk rot; 1—stalk rot present in one node; 2—stalk rot in 2 nodes; and 3—stalk rot found in 3 or more nodes. The plants dissected for stalk rot were also rated for corn borer incidence. Corn grain yields were determined by hand harvesting 20 row-ft Prom each of the 2 center rows in each plot and correcting to 15.5% moisture. Spider mites were counted by visually searching every other leaf (one half plant) of 4 plants in each plot on 7 Aug. Mites were collected from plants in each plot with a small vacuum sampler and a subsample of about 20 mites per plot was mounted for microscopic determination of mite species.