Insecticides Efficacy in Lettuce for Whitefly Control, 2016*

The objective of the study was to evaluate the efficacy of foliar insecticide spray applications for control of SWF under desert growing conditions. Leaf lettuce, ‘Jupiter’ was direct seeded on 13 Sep 2016 at the University of California Desert Research and Extension Center, Holtville, CA into double row beds on 40 inch centers. Stand establishment was achieved using overhead sprinkler irrigation initiated on 13 Sep, and irrigated via furrow irrigation was used after stand establishment. Plots were four 40 inch beds (13.3 ft) wide by 50 ft long with one non-planted bed between plots and 5 ft of bare ground between replicate blocks. Five replications of each treatment were arranged in a RCB design. Insecticidal compounds, formulations, and application rates are provided in Tables 1–3. All insecticide treatments were foliar sprays applied with a Lee Spider Spray Trac Tractor, four-row sprayer with three TJ-60 11003VS nozzles per row delivering a directed spray application at 50 psi and 63 gpa on 4 and 18 Oct 2016. An adjuvant, Dyne-Amic (Helen Chemical Company, Collierville, TN) was added at 0.1 vol/vol% to each foliar spray mixture. Numbers of SWF adults were counted on a leaf basal from five random plants in each treatment replicate and data were recorded. Numbers of SWF eggs and nymphs were counted on the abaxial leaf surface, within 2 cm² leaf disks from five basal leaves extracted from random plants within each treatment replicate and the data were recorded. A pre-treatment sample for SWF adults, eggs and nymphs were taken on 29 Sep. Post-treatment sampling for SWF adults, eggs and nymphs were collected on 6, 11, 14, 18, 21, 25, 27, and 31 Oct. Post treatment averages were calculated for SWF adults, eggs and nymphs. Data were analyzed using ANOVA. Differences among means on each sampling date were determined using protected LSD (P ≤ 0.05).

The SWF population level was lower than normal for the Imperial Valley, CA when this project was initiated. There were no differences among the treatments for SWF adults on the pretreatment sampling date of 29 Sep or on 6 and 11 Oct (Table 1). All of the insecticide treatments had significantly (P ≤ 0.05) fewer SWF adults compared with the untreated check on the post-treatment sampling dates of 18, 21, and 27 Oct and for the SPW adult PTAs. On 14 Oct, all insecticide treatment except Minecto Pro at 10 fl oz/acre had fewer SPW adults than the untreated check, and on 25 Oct all insecticide treatments except Minecto Pro at 10 fl oz/acre, and Sivanto 1.67SL at 12 fl oz/acre had fewer SPW adults than the untreated check. On 31 Oct, all insecticides had fewer SPW adults than the untreated check except Sequoia SC at 5 fl oz/acre. There were no differences among the treatment means on any of the sampling dates and no differences among the post treatment averages (Table 2). None of the insecticide treatments had fewer SPW nymphs than the untreated check on the pre-treatment sampling date of 29 Sep or on the post treatment dates of 6, 11, 14, 25, and 27 Oct (Table 3). On Oct 18, the only insecticide treatments with fewer SPW nymphs than the untreated check were Minecto Pro at 10 fl/acre, Sivanto 1.67SL at 12 fl oz/acre, and Sequoia SC at 5 fl oa/acre. On 21 Oct, all insecticide treatments had fewer SPW nymphs than the check except Sequoia SC. On 31 Oct, all insecticide treatments had fewer SPW nymphs than the check except Minecto Pro at 10 fl oz/acre and Movento 2SC at 5 fl oz/acre. All insecticide treatments had PTAs for SPW nymphs were significantly lower than the PTA for the untreated check except Exirel 10 SE at 13.5 fl oz/acre and Minecto Pro at 8 fl oz/acre. No phytotoxicity symptoms resulted from any of the insecticide treatments.

Author notes

Section Editor: John Palumbo