Insecticide Efficacy in Alfalfa Seed Production, 2013

The objective of the study was to evaluate new insecticides for their efficacy against adults and nymphs of WTPB and other insect pests on alfalfa grown for seed production under desert conditions. An insecticide efficacy trial was conducted at the UC Desert Research and Extension Center, Holtville, CA on a stand of CUF-101 alfalfa on beds of 40-inch centers; the stand was sprayed with Dibrom 8 @ 1.5 pt/acre on 20 May 2013 to control pests prior to initiating seed production. The experimental design was RCB using four replicates with 11 insecticide treatments and an untreated check. Plots were eight beds 40 ft wide by 70 ft long, with 5 ft buffers between replicate blocks. The insecticide treatments were applied on the dates at the specified rate equivalencies listed in Table 1 . The insecticide treatments were broadcast sprays applied with a Lee Spider Spray Trac, tractor mounted spray boom, equipped with 15 nozzles (TJ-60 11003VS), operated at 30 psi and delivering 36 gpa in a 20-ft wide spray swath. Hasten, a modified vegetable oil surfactant (Wilber-Ellis Company), was applied at 0.25% vol/vol in tank mixtures with each insecticide treatment. The pretreatment (PT) insect population data were collected on 30 May. Post treatment data were collected on 3, 7, 10, 14, 17, 24, and 28 Jun 2013. During each evaluation, 10 180° sweeps per plot were collected with a standard 15-inch diameter sweep net. Sweep net samples were bagged, labeled, and frozen for later counting of small WTPB nymphs (1 ^st through 3 ^rd instars), large WTPB nymphs (4 ^th and 5 ^th instars) and WTPB adults, in the laboratory. On 8 Jul 2013, mature seed pods were stripped from a few plants at random in each plot, pods were hand-threshed to prevent loss of damaged seed, and 100 random seeds from each plot were examined under a binocular microscope for WTPB damage, SB damage, ASC damage, chewing insect damage, water damage, green seed and good seed. Treatment means were analyzed using two-way ANOVA and means separated by a protected LSD ( P  ≤ 0.05).

Pre-treatment means for small WTPB nymphs, large WTPB nymphs and adult WTPB were not significantly ( P  = 0.05) different among insecticide treatments and the untreated check on 30 May ( Tables 2–4 ). There were no differences among treatments for small WTPB on 3 Jun (3DAT1), on 14 Jun (14DAT1) or on any of the sampling dates on or after 17 Jun, following the second application of insecticide treatments ( Table 2 ). On 7 Jun (7DAT1) all insecticide treatments, except GF-2628 SE, Rimon, Grandevo DF2, MBI-206EP and Grandevo DF2 to be followed by Beleaf 50 SG, resulted in fewer small WTPB nymphs compared to the untreated check. All of the insecticide treatments resulted in fewer small WTPB nymph compared to the check on 10 Jun (10DAT1). All insecticide treatments, except GF-2628 SE, Rimon 0.83EC, and Grandevo DF2 f/b Beleaf 50 SG, resulted in PTAs for small WTPB nymphs that lower than the untreated check. On 3 Jun (3DAT1), only the Beleaf 50SG and the Transform 50WG treatments resulted in means for large WTPB nymphs that were significantly lower than the untreated check mean ( Table 3 ). On 7 Jun (7DAT1), only the Transform WG treatments resulted in fewer large WTPB nymphs than the untreated check. On 10 Jun (10DAT1), only the Transform WG treatments, the Sivanto 200SL treatment and the MBI-206EP treatment resulted in fewer large WTPB nymphs than the untreated check. On 14 Jun (14DAT1), none of the insecticide treatments resulted in fewer large WTPB nymphs compared to the check. There were no differences among treatments for large WTPB on 17 Jun (3DAT2), on 24 Jun (14DAT2) or on 28 Jun (21DAT2). On 21 Jun (7DAT2), only GF-2628 SE and Beleaf 50 SG f/b MBI-206EP did not result in fewer large WTPB nymphs than the untreated check. The only insecticide treatments that resulted in large WTPB nymph PTAs lower than the untreated check were the Transform WG treatments, the Sivanto treatment, Beleaf 50SG used alone and the treatments with Beleaf 50SG f/b MBI206EP. None of the insecticide treatments resulted in fewer WTPB adults compared to the untreated check on 3, 7, 14, 24, and 28 Jun ( Table 4 ). On 10 Jun (10DAT1), all insecticide treatments, except GF-2628 SE, resulted in fewer WTPB adults than the untreated check. On 17 Jun (3DAT2) only the Transform WG treatments resulted in fewer WTPB adults than the untreated check. On 21 Jun (7DAT2), only plots treated with Transform 50WG treatments or Grandevo DF2 used alone had fewer WTPB adults than the untreated check. The only insecticide treatments that did not result in WTPB adult PTAs that were lower than the untreated check were GF-2628 SE, Rimon 0.83EC, Grandevo DF2and Grandevo DF2 r/w Beleaf 50 SG.

Only the Transform WG treatments and the Sivanto 200SL treatment resulted in higher percentages of good seed than the untreated check ( Table 5 ). The only insecticide treatment that resulted in a percentage of WTPB damaged seed that was significantly lower than the untreated check (11.25%) was Transform WG at 2.75oz/acre (5.5%). None of the insecticide treatments resulted in lower percentages of SB damaged seed, ASC damaged seed or green seed compared to the untreated check. None of the seed samples had evidence of excessive levels of water damaged seed. All insecticide treatments resulted lower percentages of chewing damage from worm pests BAW and AC compared to the untreated check. There were no symptoms of phytotoxicity following any of the insecticide treatments. This research was supported by funding from the California Alfalfa seed Production Research Board and industry gifts.

Author notes