Influence of selected spray diluents on the efficacy of n- cyhalothrin against Heliothis virescens larvae (Lepidoptera: Noctuidae)

Abstract

Insecticides have been applied to cotton in combination with a variety of diluents and agrichemicals. Preliminary studies suggested that one agrichemical or diluent can improve, have no effect, or decrease insecticidal activity compared with another diluent or agrichemical. This study investigated the effects of selected oil diluents (mineral, cottonseed and soybean) and foliar nitrogen fertilizers (urea and triazone) on the efficacy of λ-cyhalothrin against Heliothis virescens (F.) larvae. The mortality of third instar H. virescens was higher on leaf-discs when λ-cyhalothrin was applied ultra low volume (ULV) in mineral oil than when the pyrethroid was applied in cottonseed or soybean oil with a controlled droplet applicator. Larval mortality was lowest when λ-cyhalothrin was conventionally applied in water through hydraulic, hollow cone nozzles. Behavior of third instar H. virescens was observed on plants sprayed with λ-cyhalothrin in a water or mineral oil diluent. Differences in behavioral responses to λ-cyhalothrin treated plants were quite evident between the diluents. Both λ-cyhalothrin treatments reduced larval feeding on squares compared with untreated plants. The mineral oil + λ-cyhalothrin residues caused larvae to remain stationary on the leaf surface or actually abandon the treated plant surface compared with λ-cyhalothrin in water where larvae continued to move about the leaf surface and feed on the squares. Lambda-cyhalothrin was more disruptive to normal behavior when applied in mineral compared with water. Spray residues of mineral oil alone caused very little change in larval behavior when compared with behavior on untreated plants. In a field experiment, λ-cyhalothrin was sprayed on fruiting cotton plants in mineral oil, cottonseed oil, soybean oil, and water diluents. There was an overall nonsignificant trend for λ-cyhalothrin applied in mineral oil to provide the highest control of H. virescens larval numbers and the lowest larval damage to the cotton compared with λ-cyhalothrin applied in cottonseed oil, soybean oil, or water. Lambda-cyhalothrin applied in water gave the lowest control. In spray chamber experiments with mixtures of foliar nitrogen fertilizers and λ-cyhalothrin, larval mortality on leaf discs was highest when λ-cyhalothrin was applied in a spray containing triazone. Larval mortality was lower in the urea + λ-cyhalothrin applications compared with the water + λ-cyhalothrin or triazone + λ-cyhalothrin spray mixtures.