Soil systemic insecticides for control of western flower thrips on romaine lettuce, 2022

The objective of this trial was to evaluate the efficacy of soil-applied, systemic insecticides to control western flower thrips in lettuce under desert growing conditions. Romaine lettuce ‘Del Sol’ seed was direct seeded on 23 Feb 2022 at the Yuma Agricultural Center into beds on 42-inch centers with 2 seed lines per bed. All seed was planted at a 2-inch spacing. Stand establishment was achieved using overhead sprinklers and irrigated with furrow irrigation thereafter. Plots were 2 beds wide by 35 ft long and bordered by 2 untreated beds. Four replications of each treatment were arranged in an RCB design. Formulations and rates for each compound are provided in the tables. All treatments were applied to the soil at planting as a subsurface soil injection (SSI). The SSI treatments were injected 1.5 inches below each seedline at planting using a modified fertilizer shank in a total water volume of 20.5 GPA. No additional insecticide applications were applied during the trial.

WFT numbers were estimated using a whole plant wash method. On each sampling date, 5 plants on each plot were randomly selected and removed from the soil at ground level. Samples were processed using a washing technique, and the number of adults and larvae in each sample was counted using magnification. Because of heterogeneity of mean variances, data were transformed using a log10 (x + 1) function before analysis and subjected to ANOVA, and means were compared using Turkey’s HSD test (α = 0.05). Means from nontransformed data are presented in the tables.

WFT numbers were low to moderate in this trial. None of the treatments significantly reduced WFT adults on any sample date (Table 1). Verimark significantly reduced WFT larvae numbers compared with the untreated check at 27 and 34 DAP (Table 2). No phytotoxicity was observed. These results suggest that soil-applied Verimark treatment may be a practical alternative for early-season WFT control.¹

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