Cotton Insecticide Efficacy Against Sweetpotato Whitefly, 2014 *

The objective of the study was to evaluate the efficacy of various new and standard insecticides against sweetpotato whitefly (SWF) on upland cotton under desert growing conditions. Cotton was direct seeded on 22 Apr 2014 at the University of California Desert Research and Extension Center, Holtville, CA, into single-row beds on 40-inch centers. Stand establishment was achieved with furrow irrigation, and used thereafter. Plots were two beds wide by 50 ft long and bordered by one nontreated bed. Five replications of each treatment were arranged in an RCB design. Insecticide names formulations and rates treatment for each compound are provided in the tables. The applications were made on 7 and 23 July 2014 with a Lee Spider Spray Trac operated at 45 psi delivering 62 gpa. A broadcast application was delivered through three TJ-60 11003VS nozzles per bed. The adjuvant, Hasten Modified Vegetable Oil (Wilbur-Ellis Company, PO Box 16458, Fresno, CA), at 16 fl oz per acre was added to each spray mixture for all foliar spray treatments. Populations of whitefly adults, eggs, and nymphs were evaluated on: 7 Jul, pretreatment (PT) sample taken just prior to spray applications; 10 July, 3 days after treatment one (3 DAT1); 14 Jul, 7 DAT1; 17 Jul, 10 DAT1; 21 Jul, 14 DAT1; 25 Jul, 2 DAT2; 30 Jul, 7 DAT2; 1 Aug, 9 DAT2; 5 Aug, 13 DAT2. Adult populations were estimated by taking leaf turn samples recording direct counts on the undersides of leaves. Leaves selected for adult counts were fifth main stem node leaves below the plant terminus from five randomly selected plants per plot and reported as adults per leaf. Immature densities were estimated by extracting a single fifth main stem node leaf from five randomly selected plants per plot. Extracted leaves were bagged, labeled, and taken into the laboratory where densities of eggs and nymphs were counted on the abaxial surface of a 2-cm ² leaf disks from the lower left-hand quadrant of each sample leaf using a binocular dissecting microscope. Immature densities were tallied from the five 2-cm ² leaf disks on each sample date and reported as eggs or nymphs per 10 cm ² . Harvest data of seed cotton per 0.001 acres were collected on 18 Sep 2014 (one row of 13.1 ft was handpicked in each plot) and seed cotton yields are reported in lb/acre. Data sets were analyzed using two-way ANOVA and means separated by a protected LSD ( P  < 0.05).

SWF pressure was low compared to past years. There were no differences among plots for SWF adults for the PT counts taken on 7 Jul ( Table 1 ). All insecticide treatments resulted in means for SWF adults that were significantly lower than the means for the untreated check treatment on all post treatment sampling dates except on 30 Jul, 7 DAT2. The Assail 70WP at 1.7 oz/acre treatment and the Sivanto 200SL treatment significantly reduced SWF adults compared to Bifenture EC at 6.4 fl oz/acre for the PTA. All insecticide treatments resulted in fewer SWF adults than the untreated check for the PTA. There were no differences among the treatments for SWF eggs on any of the sampling dates ( Table 2 ). There were no differences among the treatments for SWF nymphs for the PT counts taken on 7 Jul, on 10 July, 3 DAT1 and on 30 Jul, 7 DAT2 ( Table 3 ). All insecticide treatments for 14 Jul, 7 DAT1; 17 Jul, 10 DAT1; 21 Jul, 14 DAT1; 25 Jul, 2 DAT2; and 1 Aug, 9 DAT2 reduced SWF nymph means compared to the untreated check mean. All insecticide treatments, except Assail + Bifenture and Bifenture at 6.4 fl oz/acre, resulted in fewer SWF nymphs than the untreated control on 5 Aug, 13-DAT2. There were no differences among the insecticide treatments for the PTA for SWF nymphs, but all insecticide-treated plots had fewer SWF nymphs than the untreated check. Only the treatments with Bifenture alone applied at 6.4 fl oz/acre and the Pyrifluquinazon treatment did not improve seed cotton yield compared to the untreated check ( Table 4 ). Assail 70WP applied at 1.7 oz/acre resulted in greater mean seed cotton than all other insecticide treatments, except Sivanto 200 SL applied at 10 fl oz/acre. No observable symptoms of phytotoxicity resulted from any of the insecticide treatments.

Author notes