Miticide Efficacy Against Twospotted Spider Mites on Watermelon, 2018

The objective of this experiment was to evaluate the efficacy of miticides for control of TSM on watermelon. ‘Bottle Rocket’ watermelons were transplanted on 30 May at the University of Delaware Carvel Research and Education Center (CREC) in Georgetown, DE using a water wheel. Plots consisted of two rows on 7-ft centers, 20-ft long, and plants spaced 3 ft apart. Every third plant was the pollinizer variety ‘SP-7’ pollenizer. Watermelons were maintained according to commercial standard practices. On 14 Jun, plots were infested with twospotted spider mites originally sourced from a greenhouse at CREC. All plots were treated on 27 Jun with Sevin (carbaryl) to flare spider mites. Plots were treated on 10 Jul using a CO2-pressurized backpack sprayer equipped with an 8-nozzle boom with 20-inch spacing. The sprayer was calibrated to deliver 40 gpa through D4 tips and 45 cores at 52 psi. The nonionic surfactant Induce (Helena Agri-Enterprises, Collierville, TN) was applied with each treatment at a rate of 3 pints per 100 gal of water. Plots were arranged in a randomized complete block design with four replicates. Eggs and mobiles from the underside of 10 crown leaves from each plot were sampled on 9 Jul (precount) and again 3, 6, 13, and 20 days after treatment (DAT). Data were square-root transformed (precounts, 3 DAT, 6 DAT mobiles) or log-transformed prior to ANOVA in SAS JMP. Tukey–Kramer HSD was used for means separation. Presented are nontransformed means. TSM populations were extremely high for the duration of the trial and increased 10-fold from the week prior to treatment. The greatest reductions in TSM populations were observed in the Kanemite plots which had numerically greater initial populations. Minecto Pro had significantly fewer mobiles than the untreated check on 6, 13, and 20 DAT, whereas Zeal differed from the untreated check 20 DAT. All other products resulted in insignificant reductions (Table 1). Reductions in egg counts closely followed reductions in mobile counts (Table 2). No phytotoxicity was observed. Means in the same column followed by the same letter are not significantly different (Tukey–Kramer HSD; P > 0.05). Means in the same column followed by the same letter are not significantly different (Tukey–Kramer HSD; P > 0.05). Means in the same column followed by the same letter are not significantly different (Tukey–Kramer HSD; P > 0.05). Means in the same column followed by the same letter are not significantly different (Tukey–Kramer HSD; P > 0.05). This research was supported in part by industry gifts of product.