Insecticide Efficacy for Chilli Thrips Management in Strawberry, 2019

Abstract

(Hillsborough County). Bare-root short-day strawberry cultivar, 'Brilliance', was planted on 8 Oct 2019 in 32-ft-long strawberry plots with 10 ft buffer in a randomized complete block design. There were 50 plants per plot planted at 12-inch plant spacing. Five treatments and one untreated check were replicated four times in this study. Experimental plot maintenance involved the application of DiPel DF (2 lb/acre) for armyworm, Spodoptera spp. (Lepidoptera: Noctuidae) on a weekly basis from 18 Oct to 20 Dec, which was applied separately from treatments. All experimental products were tank mixed with a sur-factant, Induce, at the rate of 0.25% (v/v). The application was done with the help of a backpack sprayer calibrated to 50 gallons per acre (GPA) and the applier used a metronome to calibrate their pace during insecticide application. The pretreatment sampling was conducted on 3 Dec 2019. Insecticide treatments were applied on 4 Dec 2019 thereafter. Posttreatment sampling was conducted on 10, 18, and 24 Dec. Since chilli thrips prefer feeding on young foliage, young strawberry leaflets and flowers were collected from six random plants per plot in sealed bags and washed in 70% ethanol for counting of nymphs and adults on each sampling date. Each plot was assigned a damage rating on each sampling date. Fruits were also harvested on each sampling date followed by grading of fruits into marketable and damaged fruit and weighed. Generalized linear-mixed model was used to model the effects of treatments on insect count, plant damage rating, and marketable yield (SAS 9.4, SAS Institute Inc. 2018). Data were fitted to Poisson distribution and normality of residuals were confirmed with diagnostic plots/student panels. Separation of means was done using the Tukey HSD test (α ≤ 0.05). The pretreatment values of all the variables did not differ among treatments. The effect of treatments was evident on chilli thrips adults and nymphs on leaflets at 14 and 20 DAT, on nymphs on flowers at 6 DAT (Tables 1 and 2), and on seasonal mean of marketable yield (Table 3). Season end plant damage rating was not affected by insecticide treatments. Radiant significantly reduced chilli thrips adults and nymphs on leaflets at 20 DAT, and nymphs on flowers at 6 DAT compared to untreated check. Low rate of Exirel showed significant suppression of chilli thrips nymphs on leaflets at 14 DAT and high rate of Exirel significantly reduced both adults and nymphs on leaflets at 20 DAT. At 20 DAT, all insecticide treatments except Exirel at low rate, suppressed adults on leaflets compared to untreated check. Radiant had significantly high marketable yield compared to all other treatments. Results indicate that Radiant showed promising control of both adults and nymphs with significantly high marketable yield. After Radiant, Exirel at high rate showed promising control of both adults and nymphs. Therefore, Exirel can be rotated in spray program to reduce the selection pressure on insect pests. No phytotoxicity was observed. 1 1