Control of the Cabbage Looper and Corn Earworm with Nuclear Polyhedrosis Viruses12

Abstract

Small-scale field experiments at College Park, Maryland, during 1966 indicated that on the basis of dosage per acre, the nuclear polyhedrosis virus (NPV) of the cabbage looper, Trichoplusia ni (Hübner), is much more effective than the NPV of the corn earworm, Heliothis zea (Boddie), in controlling their respective hosts. Fresh preparations of cabbage looper virus were more effective at lower dosages than commercial preparations in reducing the numbers of cabbage looper larvae in mature broccoli heads. Significantly better control of cabbage looper was attained with the commercial preparations of virus as the dosage was increased from 3 to 12 larval equivalents per acre. At the lower doses fresh virus preparations were significantly better than commercial preparations and were equal to them at the highest dose. Control of cabbage loopers decreased as the intervals between applications increased from 7 to 21 days. T. ni NPV sprayed in conjunction with dimethoate gave excellent control of all pests of broccoli. Both malathion and RP 11783 (O,O-dimethyl phosphorodithioate S-ester with 3-(mercaptomethyl)-2-benzoxazolinone) sprayed in combination with T. ni NPV also resulted in good control of all broccoli pests. The effectiveness of the corn earworm NPV for control of earworm increased as the rate of application was increased from 25 to 100 larval equivalents/acre. Control of earworm decreased as the intervals between application increased from 7 to 21 days.