Control of Cabbage Caterpillar Pests with a Soil Drench of Coragen, 2015

The study was conducted to examine whether a single soil drench after transplanting could provide full-season control of the cabbage caterpillar complex. The study was carried out at the Plant Science Research and Teaching Facility at the University of Connecticut in Storrs, CT. Single rows of “Bravo” cabbage seedlings were transplanted into plastic-mulched beds on 18 May and harvested on 14 Aug. Plants were drenched with approximately 8 oz of water immediately after transplanting and were not irrigated again. Treatment plots consisted of 20 plants each, replicated four times in a RCBD, in two rows, with plants spaced at 1 foot within rows and 6 feet between rows. Treatment plots were either drenched with a 2-oz Coragen solution at the 5-oz per acre rate, or left as an untreated check. The drench was applied on 28 May to the base of each plant with a CO ₂ backpack sprayer with the nozzle and screen removed. The sprayer was calibrated to deliver approximately 2 oz of the mixed solution per plant. Weather during the study was dry in May, Jul and Aug, and wet during Jun, which could have leached some of the insecticide from the root zone. Five randomly selected plants per plot were sampled on 26 Jun and 11 Aug, and three plants per plot were evaluated on 24 Jul. From these samples, infested plants were counted on 26 Jun and 24 Jul and the percent infested plants per plot were calculated. Caterpillars and pupae were identified and counted on 24 Jul, and plant damage and marketability was rated at harvest on 11 Aug, on a scale of 0–5 (severe to no damage). Plants rated < 3 had damage to the head and/or wrapper leaves and were considered unmarketable. Data were analyzed using Friedman’s test ( P  = 0.05).

Insect pressure was light to moderate during the trial. On 26 June, there was a significant difference between the percent infested plants in the treatments: 15% of the Coragen drenched plants, and 100% of the untreated check plants, were infested ( Table 1 ). On 24 July, 92% of the check, and 25% of the drenched plants were infested, but the differences were not significant. ICW, DBM, CL larvae and/or pupae were present in Jul ( Table 2 ). There were significantly more DBM and total larvae and pupae on check plants than on Coragen treated cabbage on 24 July. Coragen drenched cabbage had a mean of 0.5, and check plots 2.0, caterpillars and pupae per plant. There was significantly less plant damage and more marketable heads in Coragen plots than in check plots on 11 Aug. Eighty percent of the cabbage heads in the Coragen treatment were marketable at harvest, and 70% of the heads in the untreated check were unmarketable. A single soil drench of Coragen after transplanting did not provide complete caterpillar control until harvest.

Author notes