Insecticide Efficacy Against Whitefly in Watermelon, 2016*

The objective of the study was to evaluate the efficacy of various insecticides, insecticide rotations, types of application (soil drench or foliar sprays), and timing of applications for SWF control on watermelon under desert growing conditions. An insecticide trial was established at the University of California Desert Research and Extension Center, Holtville, CA, using a stand of watermelon variety ‘Sugar Baby’ direct seeded into single row beds, 80-inch centers, on 24 Mar 2016. Stand establishment was achieved using drip irrigation, which was used thereafter. Plots were two beds wide (13.33 ft) by 50-ft long and bordered by one nonplanted, bare bed, and 10-ft bare ground buffers between replicate blocks. Included were an untreated check and nine insecticidal treatments, applied as soil drench at the base of the plant or as a foliar spray, in an RCB design experiment with four replicates. All soil drench insecticide treatments were applied on 5 Apr 2016 with a single TJ-8001.5 nozzle delivering 6.9 gpa at 30 psi concentrated into a 1inch band at the base of the plants. The first foliar sprays were applied using a handheld, CO₂ propelled, single-row sprayer with two TJ-8001.5 nozzles per row, delivering 13.6 gpa at 30 psi. The second sprays were applied using a handheld, CO₂ propelled, single-row sprayer with three TJ-8001.5 nozzles per row, delivering 20.3 gpa at 30 psi and third foliar sprays were applied with a Lee Spider Spray TracTractor setup to treat two rows with three TJ-60 11003VS nozzles per row delivering 46.3 gpa at 40 psi. The application dates for each foliar insecticide are shown in Table 1. Whitefly adults were sampled by examining the fifth leaf back from a cane tip on ten random plants per plot. Whitefly eggs and nymphs were counted using a binocular microscope in the laboratory within one-leaf disk of 2-cm² on the abaxial leaf surface in the lower left quadrant from five melon leaves extracted from random plants per plot. Seasonal trial averages were calculated for each treatment for adults, eggs and nymphs and are shown in the table. The first harvest initiated on 15 Jun and continued on 22 Jun; data from the five harvest dates are pooled. The total numbers of fruit and weight of fruit in kg/0.002 acre were recorded for each treatment replicate. Brix were measured for each fruit using a refractometer (American Optical Corp., Buffalo, NY). Data were analyzed using ANOVA. Differences among means on each sampling date were determined using LSD test (P < 0.05).

None of the insecticide treatments had SWF means lower than the check mean on 12 and 20 Apr (Table 2). All of the insecticide treatments had lower SWF adult means on 27 Apr, 6, 11, and 23 May and for the season averages compared to the untreated check (P < 0.05). All insecticide treatments except Sivanto followed by Pyrifluquinazon 20SC followed by Brigade 2EC followed by Oberon 2SC had lower SWF adult means compared to the untreated check on 30 May. All insecticide treatments except Venom followed by Oberon + Requiem EC followed by Exirel, and followed by Sivanto had lower SWF adult means compared to the untreated check on 7 Jun. There were no differences among the treatments for SWF egg means on 12 Apr, 6, 11, 23, and 30 May (Table 3). On 20 Apr, only the Exirel treatment to be followed by Pyrifluquinazon 20SC did not have fewer eggs than the untreated check. On 27 Apr, only the Exirel treatment to be followed by Oberon 2SC and the Sivanto treatment to be followed by Pyrifluquinazon 20SC had fewer eggs than the untreated check. All of the insecticide treatments had fewer SWF eggs compared to the check on 7 Jun (P < 0.05). All insecticide treatments except Venom followed by Pyrifluquinazon 20SC had SWF eggs season averages that were lower than the season average for the untreated check. There were no differences among the treatments for SWF nymph means on 12, 20, and 27 Apr or on 6 and 23 May (Table 4). On 30 May, all insecticide treatments had fewer SWF nymphs than the untreated check except Venom followed by Oberon+ Requiem EC followed by Exirel followed by Sivanto and Sivanto followed by Pyrifluquinazon 20SC followed by Brigade 2EC followed by Oberon 2SC. All insecticide treatments resulted in nymph means that were lower than the check mean on 7 Jun (P < 0.05). All insecticide treatments resulted in seasonal average for nymphs that were lower than the untreated check untreated seasonal average. All insecticide treatments except Eirel followed by Pyrifluquinazon 20SC had SWF nymphs season averages that were lower than the season average for the untreated check. There were no differences (P < 0.05) among the treatments for numbers of fruit or for weight of fruit. (Table 5). Only the treatment Venom followed by Pyrifluquinazone 20 SC followed by Exirel had a higher Brix value than the untreated check. There were no symptoms of phytotoxicity following any of the insecticide applications.

Author notes

Subject Editor: John Palumbo