Comparison of Foliar Insecticide Alternatives for Control of Lepidopterous Larvae in Head Lettuce, 2014 *

The objective of this trial was to compare the efficacy of foliar insecticide alternatives currently used in conventional lettuce production under fall growing conditions. Head lettuce “El Guapo” was direct seeded into double row beds on 42-inch centers on 6 Sep 2014. Plots were two beds wide by 40 ft long and bordered by two untreated beds. Stand establishment was achieved using overhead sprinkler irrigation, and irrigated with furrow irrigation thereafter. Four replications of each treatment were arranged in a RCB design. Formulations and rates for each compound are provided in the tables. Three foliar sprays were applied on 5, 17 Oct, and 12 Nov with a CO ₂ pressurized boom sprayer that delivered a broadcast application through two TXVS-18 ConeJet nozzles per bed at 40 psi and 22.5 gpa. An adjuvant, Dyne-Amic (Helena Chemical Co.), was applied at 0.125% vol/vol with these spray treatments. At various intervals after treatment (DAT), 10 plants were randomly selected from each replicate and destructively sampled for the presence of each insect species. BAW and CL control was based on the examination of whole plants for presence of large (second instar or older) larvae. At harvest (24 Nov), estimates of head contamination were made by examining 10 mature heads (plus two wrapper leaves) from each plot for presence of feeding damage, frass, and lepidopterous larvae. Incidence of any of these would result in the head being contaminated and likely unmarketable. Because of heterogeneity of mean variances, BAW and CL data were transformed using a log ₁₀ ( x  + 1) function before analysis and subjected to ANOVA (Proc GLM; SAS Institute 2009). Means were compared using an F -protected LSD ( P  ≤ 0.05). At harvest, data for head contamination were converted to percentages by dividing the total number of contaminated heads by the total number of heads examined ( n  = 10). Percent contaminated head data were subjected to arcsine square root transformation before analysis. Means were compared using Turkey’s HSD test ( P  ≤ 0.05). Means from non-transformed data are presented in the tables.

CL numbers were very low following the first application and differences among treatments were not observed until 11 DAT-1 where larvae numbers in the Proclaim and Belt treatments did not differ from the non-treated check ( Table 1 ). Thereafter, differences among treatments and the non-treated check were observed. Overall, Proclaim and Belt provided the least consistent CL control. BAW was consistently heavy following the first and second applications. All treatments, except Belt at 1 DAT-1, significantly reduced BAW numbers compared to the non-treated check ( Table 2 ). Following the third application, control was less consistent. Overall, Exirel and Radiant provided the most consistent BAW control. Harvest quality evaluations showed that all spray treatments provided significant reductions in head contamination relative to the non-treated check, except for head damage in the Proclaim treatment ( Table 3 ). No phytotoxicity symptoms were observed following any of the insecticide treatments.

Author notes