Evaluation of Foliar Broadcast Insecticides for Control of Thrips in Peanut, 2016*

Selected foliar broadcast insecticides were evaluated for control of thrips in peanut. “Wynne” peanut was planted 11 May at the Virginia Tech Tidewater Agric. Res. & Ext. Ctr., Suffolk, VA, using 36-inch row spacing. All seed were treated with fungicide. Foliar applications were broadcast twice (when peanut seedlings cracked ground on 1 Jun and again on 8 Jun) with a CO₂-pressurized backpack sprayer calibrated to deliver 14.3 gpa at 18 psi through 8002EVS nozzles spaced 18 inches apart on the spray boom. No adjuvant was applied with the products. A randomized complete block experimental design was used with four replicates; plots were four rows by 35 ft. Thrips injury to plants was estimated by visually rating injury using a 0 to 10 scale, where 0 = no injury, 1 = 10% leaves injured, 2 = 20% leaves injured, 3 = 30% leaves injured, 4 = 40% leaves injured, 5 = ≥ 50% leaves injured and ≤ 5% terminal buds injured, 6 = ≥ 50% leaves injured and 25% terminal buds injured, 7 = ≥ 50% leaves injured and 50% terminal buds injured, 8 = ≥ 50% leaves injured and 75% terminal buds injured, 9 = ≥ 50% leaves injured and 90% terminal buds injured, and 10 = dead plants. Thrips counts were determined by collecting ten unopened terminal leaflets per plot in vials containing 30 ml soapy water, teasing the leaflets open, and counting TT under a stereoscope following suction filtration. The number of plants with visual symptoms of Tomato spotted wilt (TSW) was determined by examining two rows per plot on two dates. Peanuts were dug on 19 Oct and harvested 27 Oct. Yields were determined by combining peanuts from two rows of each plot and adjusting to 7% moisture. Data were analyzed using ANOVA and LSD statistical procedures.

All of the insecticide treatments resulted in significantly less thrips injury compared to the untreated check on both sample dates (Table 1). There were no significant differences among treatments for numbers of adult thrips on either sample dates or for immature thrips on 7 Jun. All of the insecticide treatments resulted in significantly fewer immature thrips than the untreated check on 14 Jun. There were no significant differences among treatments for TSW hits or yield.

Author notes

Subject Editor: Donald Cook