Insecticidal control of late winter/spring alfalfa pests in the Palo Verde Valley, 2001

Abstract

Fifteen insecticide treatments were applied March 12, 2001, to compare their efficacies on alfalfa weevils, western flower thrips, blue alfalfa aphids and associated aphid predators. Furadan and insecticides containing a pyrethroid active ingredient reduced alfalfa weevil larvae by more than 89% when compared with the untreated check. All treatments provided a minimum of 70% control of blue alfalfa aphids by seven days post treatment, with fewest aphids noted in WarriorT insecticide treatments. Although some insecticides reduced adult western flower thrips number initially, adult thrips increased in all plots between four and seven days post treatment. Both treatments that contained Lorsban had significantly more adult thrips than the untreated check, indicating that low amounts of this insecticide may attract adult western flower thrips. At both four and seven days post treatment, nymphal thrips control was best in Success, followed by Furadan, dimethoate and treatments containing Lorsban. Higher numbers of thrips nymphs were noted in all pyrethroid treatments not in combination with other treatments than in the untreated check at four and seven days post treatment, perhaps indicating hormolygosis for western flower thrips and these insecticides. Few aphid predators were present until late in the study.