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Evaluation of insecticides for control of worm pests in alfalfa

Several species of worm pests common in California alfalfa include beet armyworm, alfalfa caterpillar, and alfalfa webworm. An insecticide efficacy trial for the evaluation of worm pest control was conducted at the UC Desert Research and Extension Center on a stand of CUF-101 alfalfa.

The experimental design was Randomized Complete Block using 4 replicates with 8 treatments and the plots measured 50 ft × 13.3 ft. Test materials were applied on Sept. 11, 2007 at the specified rate equivalencies. Pretreatment evaluations of insect populations in each plot were collected on Sept. 7, 2007. Post-treatment evaluations were collected on Sept. 12, 14, 18, 25, and Oct. 5, 2007, or 1, 3, 7, 14, and 24 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 worm pest larvae by species. Data was analyzed using ANOVA and means separated using Least Significant Difference Test (P=0.05).

Pre-treatment numbers of all worm pests were similar (P=0.05) among treatments. All insecticide treatments had means for beet armyworm that were significantly (P=0.05) lower than the means for the untreated control 1 and 14 DAT, but there were no differences among the means and the untreated control 24 DAT.

All but Lorsban 4E @ 32 fl oz/acre had means for beet armyworm that were significantly lower than the means for the untreated control 3 DAT, and all but Lorsban 4E @ 32 fl/acre and GF 2153 @ 64 fl oz/acre had means for beet armyworm that were significantly lower than the untreated control 7 DAT.

The numbers of alfalfa caterpillar and webworms were low on all sampling dates and there were no differences among the insecticide treatments and the untreated control. However, the post treatment averages for alfalfa caterpillar were lower than the untreated control for all insecticide treatments except Lorsban 4e @ 32 fl oz/acre.

In conclusion, all insecticide treatments provided some level of control for beet armyworm and alfalfa caterpillar, but Lorsban at the low rate appeared to be the least efficacious.

To review the related tables in this research, visit the Imperial County Cooperative Extension Web site and click on the May 17, 2008 newsletter located at

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