Control of the Cabbage Looper with a Virus Disease1

Abstract

Laboratory and field experiments showed that the virus which causes polyhedrosis of the cabbage looper (Trichoplusia ni (Hbn.)) is a highly virulent pathogen. In laboratory tests an oral dosage of 0.001 ml. of an inoculum prepared by triturating the body contents of one virus-killed fifth-instar cabbage looper in 16 liters of water caused infection and death of all larvae treated. Field tests on cabbage, cauliflower and broccoli were conducted in which virus-killed cabbage loopers were triturated in water and applied at rates from 0.94 to 120 larvae per acre with a low volume sprayer applying 30 gallons per acre. In all of the four field experiments it was possible to initiate a polyhedrosis epidemic and thereby greatly reduce the cabbage looper population in such test plots. Although increased dosage caused more rapid disease progress, a dosage of 0.94 larva per acre initiated a polyhedrosis epidemic. Six months storage of the inoculum at 0° F. did not cause any apparent reduction in pathogenicity nor was there any adverse effect noted when TEPP or spreader-sticker (Rohm & Haas B-1956) was added to the inoculum when applied.