Chemical Control of Thrips and Aphids on Cotton, 1985

Abstract

Abstract Cotton was planted 19 Apr on rows spaced 40 inches apart. Caparol was applied premergent at 2.4 lb (AI)/acre on 19 Apr. Plots were arranged in a randomized block design with treatments replicated 4 times. Plots were 8 rows wide and 40 ft long. Blocks were separated by 15 ft of untreated cotton. The study was bordered in front and back by a 25 ft buffer of untreated cotton. Foliar treatments were applied to the inner 4 rows of designated plots. A backpack sprayer calibrated to deliver 5 gal of solution per acre through two HC-4 nozzles per row at 36 psi and 3 mph was used to apply foliar insecticide treatments. Temik treatments were applied to all 8 rows of designated plots. A 2-row Gandy applicator was used to apply Temik treatments at planting. Foliar treatments were applied 1 and 8 May. Density of thrips and aphids were determined 30 Apr, 7 and 13 May. Density levels were assessed by counting thrips (adults and nymphs) and aphids on 15 randomly selected plants per plot. This was accomplished by emersing plants one at a time in a jar containing 75 percent ethyl alcohol. Thrips were easily dislodged but agitation was required to remove aphids. Number of thrips (adults and nymphs) and aphids were determined by counting them under a microscope. Phytotoxicity of the tested insecticides was assessed by counting plant population density in two 13.1-row-foot sections per plot. Thrips damage ratings were made by averaging ratings of 10 plants per plot (5 plants from each 13.1-row-foot section). Plants rated were selected using a random number table. Plants were rated on a scale of 1 (no visible thrips damage) to 7 (terminal destroyed). Damage ratings were made 13 May. Soil samples to determine nematode density were taken 5 Jun. Four subsamples per plot were mixed together and one sample taken from this mixture. Samples were submitted to the Texas Plant Disease Diagnostic Laboratory at College Station, Texas on the Texas A&M University campus for nematode density dertermination. Cotton fruiting rates were assessed by taking square, bloom, and boll counts. The number of squares per 10 plants was counted and recorded for each plot, 5 Jun, about 1 wk into the squaring period. A count of blooms and bolls was made on two 13.1-row-foot sections per plot 27 Jun, 9 days after first bloom. Yield data was gathered from stratified harvest of two 13.1-row-foot sections per plot. All plots were treated with Cygon on 28 May and 4 Jun for control of cotton fleahopper. Cythion RTU was applied 7 and 13 Jun, and 2 Jul for control of boll weevil. Ammo was applied for control of Heliothis spp. 1 and 10 Jul.