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EFFICACY OF INSECTICIDES FOR
WORM PEST CONTROL IN ALFALFA, 2008
Eric T. Natwick

An insecticide efficacy trial was conducted at the UC Desert Research and Extension Center on a stand of CUF-101 alfalfa. The objective of the study was to evaluate the efficacy of the new and older insecticidal compounds used against larvae of lepidopterous pests (Beet armyworm (BAW), Spodoptera exigua (Hübner), Alfalfa caterpillar (AC) Colias eurytheme Boisduval, and Alfalfa webworm (AWW) Loxostege cereralis (Zeller)) on alfalfa grown for hay production under desert growing conditions. The experimental design was randomized complete block (RCB) using four replicates with eight insecticide treatments and an untreated check. Plots were 25 ft wide by 50 ft long. Formulations and rates for each compound are provided and test materials were applied on 5 Aug 2008 at the specified rate equivalencies listed in the tables. Broadcast applications were delivered through 12 TJ-60 11003VS nozzles using a Lee Spider Spray Trac operated at 40 psi delivering 38 gpa. An adjuvant, Penetrator Plus (Helena Chemical Co.), was applied at 0.1% v/v with all treatments. Pretreatment (PT) evaluations of insect populations in each plot were conducted on 5 August. Post treatment evaluations were made on 8, 12, 19 & 26 August or 3, 7, 14 and 21 days after treatment (DAT). During each evaluation, ten sweeps per plot were collected with a standard 15-inch diameter sweep net. Sweep samples were bagged, labeled, and frozen for later counting of BAW, AC, and AWW larvae (Tables 1 - 3). Treatment means were analyzed using 2-way ANOVA and means were separated by a protected LSD test (P=0.05).
Pretreatment numbers of BAW larvae were similar (P=0.05) among treatments (Table 1). BAW means for all insecticide treatments were significantly lower (P=0.05) than the untreated check 3 and 7 DAT. All insecticide treatments, except Intrepid (6 fl oz) and Baythroid, had significantly lower beet armyworm means than the untreated check 14 DAT, and only the three rates of Belt 480 SC had means significantly lower than the untreated check 21 DAT. Beet armyworm post treatments averages for all treatments but Baythroid were lower than the untreated check.
Alfalfa caterpillar means were significantly lower (P=0.05) in all insecticide treatments compared to the untreated check 3 DAT and 7 DAT (Table 2). All insecticide treatments, except Intrepid (6 fl oz), had significantly lower alfalfa caterpillar means than the untreated check 14 DAT. None of the insecticide treatments had means for alfalfa caterpillar that were significantly lower than the mean for the untreated check 21DAT. All insecticide treatments had post treatment averages for alfalfa caterpillar that were significantly lower than the check.
None of the insecticide treatments had alfalfa webworm means that were significantly lower (P=0.05) than the untreated check until 7 DAT when all but Lorsban Advanced were lower than the check (Table 3). All insecticide treatments for AWW means were significantly lower than the untreated check 14 DAT. None of the insecticide treatments had means that were significantly lower than the mean for the untreated check 21 DAT, but all insecticide treatments had post treatment averages that were significantly lower than the check.
Belt 480 SC provided superior AWW pest control, but is not currently registered for this use. Baythroid did not perform
well against BAW.