Effects of Insecticide Sidedress Placement, 1988:

Abstract

Abstract Field tests were conducted to determine whether placement of fertilizer shanks for delivery of fertilizer, insecticide, or both affected broccoli yields or efficacy of control of PPGA. Broccoli was direct seeded into double rows spaced 10 inches apart on 40-inch beds on 24 Sep 1987 in a Hidalgo fine sandy loam in Monte Alto, Tex. Plants were thinned to a 4-inch spacing on 12 Oct, and the crop was irrigated (furrow flood) as needed to avoid water stress. The experiment was arranged in a randomized complete block design with 8 treatments and 4 replications. Each plot consisted of 4 beds, 70 ft long; 10-ft alleys separated replications. Treatments consisted of applications of a liquid fertilizer solution (32-0-0) delivered with varying number of fertilizer shanks (knives) per bed. For each bed, there was 1 shank (between rows only), 2 shanks (on 2 outside margins of rows), or 3 shanks (between and on the outside of each row). The outside fertilizer shanks were positioned 3-6 inches from the plants. Fertilizer was applied as a sidedress either alone or in combination with an insecticide. There were 2 control plots; one received no insecticide or fertilizer, the other received only a foliar application of a systemic aphicide. A commercial liquid fertilizer applicator calibrated to discharge 25 gal/acre delivered the sidedress treatments 1-3 inches below the soil surface. The foliar spray was applied with a tractor-mounted sprayer equipped with a CO2-powered system fitted with a single-cone nozzle/bed and calibrated to deliver 20 gal/acre on a 20-inch band. Applications were made when plants were at the 6-8-leaf stage on 29 Oct. Soil temperature at application was 27°C. PPGA density was estimated using a simple flotation technique; roots from 5 randomly selected plants were immersed in a calcium chloride solution (1 tablespoon CaCl in 1 gal water), and insects floating to the surface were counted. A pretreatment sample was made on the day of application, and subsequent samples were made at 2-wk intervals until harvest. Yields were determined by hand-harvesting a 20-ft subsample in two beds near the center of each plot. Only broccoli heads of commercially acceptable maturity were harvested during each of 3 harvests. Yield data were combined for each successive harvest to provide cumulative totals. All data were analyzed using ANOVA, and means were separated using LSD.