Efficacy of foliar-applied insecticides for the control of lepidopteran pests in tomatoes in Virginia, 2024

The efficacy of selected insecticides on lepidopteran pests of tomatoes was evaluated at the Virginia Tech Homefield Farm in Whitethorne, Virginia (Montgomery County). Tomatoes (Mountain Fresh) were transplanted on 9 June 2024. Plot size was 1 row by 20 ft grown on white plastic mulch with drip irrigation and no guard rows. Treatments were replicated four times in an RCB. All foliar treatments were applied with a single-nozzle boom equipped with 8003VS spray tip powered by a CO₂ backpack sprayer at 40 psi delivering 30 gpa. The applicator sprayed both sides of the staked row going up and down plants. All treatments included Dyne-Amic adjuvant at 0.25% v:v. All plots were treated weekly for 4 wk beginning at fruiting: 22 July (application 1), 29 July (application 2), 8 August (application 3), and 15 August (application 4). On 5 August and 20 August, full-sized but green or red tomato fruit were hand-harvested from plots and a sample of 30 fruit was examined for insect feeding damage. The number of fruits with lepidopteran chewing holes was recorded. All data were analyzed using analysis of variance procedures. Means were separated using Fisher’s LSD at the 0.05 level of significance. Data were sqrt transformed to normalize variance when necessary.

Lepidopteran pests included a mix of mostly 70% tomato fruitworm (Helicoverpa zea), 20% tobacco hornworm (Manduca sexta), and 10% yellowstriped armyworm (Spodoptera ornithogalli). Lepidopteran chewing damage to fruit averaged ~17% in the untreated check plots in the two harvests on 5 August and 20 August (Table 1). There was a significant treatment effect of this damage on both harvest dates. On 5 August, all insecticide treatments except Intrepid 2F had significantly less damage than the untreated check. On 20 August, all insecticide treatments had significantly less damage than the untreated check. No signs of phytotoxicity were observed.¹

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