Foliar Insecticide Efficacy Against Western Flower Thrips in Staked Tomato, 2019 Open Access

The objective of this study was to compare the efficacy of various foliar insecticide treatments for the management of immature and adult western flower thrips (WFT) on staked tomatoes. The trial was conducted from 9 to 31 Jul 2019 in a commercial staked tomato field in Woodleaf, North Carolina, with a history of high WFT populations. Tomato ‘Mountain Fresh’ transplants were set into bare ground the first week of May, watered as needed with overhead irrigation, and sprayed with a standard fungicide program. The trial was established in a 0.6-acre section of an approximately 6-acre field in which plots consisted of a 25-ft-long section of a tomato row. Plants were spaced 1.5 ft apart within rows, which were 5 ft apart. Treatments within the same replicate were placed in the same row and treatment rows were separated by an untreated row. Each treatment consisted of four replications and were arranged in an RCB design. The evaluated insecticides and untreated check are listed in Tables 1 and 2. Each treatment was sprayed with a CO₂-powered backpack sprayer delivering 62 gallons per acre through four hollow cone nozzles per row at 40 psi—each treatment was sprayed with a 2-nozzle wand on each side of the row. Treatments were applied on 9, 16, and 24 Jul.

Counts of immature and adult thrips were recorded on 12, 16, 23, and 31 Jul (3 and 7 days after the first treatment application, and then again at 7 days after the second application and 8 days after the third application). Thrips were sampled by removing 10 leaflets per plot from a mature leaf located in the upper half of the plant and rinsing each leaflet in a 100 ml plastic cup containing approximately 70 ml of 50% EtOH. Samples were returned to the laboratory where thrips were counted under a stereo microscope. Season total cumulative thrips days were calculated by multiplying the average density on successive sample dates by the sampling interval (days) and adding all thrips days over all sample dates. Number of thrips were log₁₀(x+1)-transformed and analyzed within each sampling date and life stage using ANOVA and means were separated using LSD (P = 0.05).

At the time of first application of treatments on 9 Jul, thrips populations averaged 16.1 ± 2.3 (SEM) adults and 47.4 ± 5.4 (SEM) immature thrips per 10 leaflets, collected from eight random samples across all four replicates. Immature thrips in the non-sprayed check increased to a peak density of 89.5 ± 7.8 thrips per 10 leaflets on 16 Jul, and then declined to <20 per 10 leaflets on 23 and 31 Jul (Table 2). Adult populations in the non-sprayed check reached their peak density on 12 Jul (29.8 ± 6.1) and then declined over the remaining weeks to 7.0 ± 1.9 on 31 Jul. At 3 DAT following the first application, none of the treatments significantly reduced the number of immature thrips, although the number of adults was reduced by the application of Beleaf (Table 2). On 16 Jul (7 DAT), Beleaf, Harvanta, and Torac all significantly reduced densities of immature thrips, while there were no differences among treatments in adult densities. Following the second and third application of treatments, counts were highly variable among treatments, and Beleaf was the only treatment to significantly reduce thrips counts below the check. Season total cumulative thrips days (based on both adult and immature thrips counts) are shown in Table 2 and illustrate that Beleaf was the most effective treatment tested in reducing thrips populations. Harvanta, Torac, Grandevo WDG, and Venerate SC also significantly reduced thrips numbers below the check.¹

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