Evaluation of insecticides for the control of Helicoverpa armigera (Hubner) and Helicoverpa punctigera (Wallengren) (Lepidoptera: Noctuidae) on soybean, and the implications for field adoption

Seven insecticides were evaluated against first-, third- and fifth-instar Helicoverpa armigera (Hubner) and Helicoverpa punctigera (Wallengren) larvae using a leaf-disc bioassay of field-treated soybean. Significant differences were detected in age-specific mortality, time to effect (LT50) and field persistence of the insecticides tested. With the exception of trichlorfon, the mortality of first-instar larvae was similar in the different treatments to the commercial standard, methomyl. The mortality of third- and fifth-instar larvae in the spinosad and chlorpyrifos treatments was also similar to that in the methomyl treatment, while the age-specific mortality of the insecticides based on Bacillus thuringiensis and nucleopolyhedrovirus declined more rapidly, resulting in low mortality to fifth-instar larvae. The LT50 Of the biological-based products were significantly greater than those of the conventional products. Only chlorpyrifos showed significant activity 1 week after treatment. The results suggest the need for a user education program to highlight the likely differences in the field performance of the newer biological-based products compared with the conventional chemicals with which growers are familiar.