(E11) CABBAGE: Brassica oleracea capitata L. 'Grand Slam' Cabbage looper; Trichoplusia ni Hübner Diamondback moth; Plutella xylostella L. Tong-Xian Liu Texas Agric. Exp. Station 2415 E. Highway 83 Weslaco, TX 78596 Phone: (956) 968-5585 Email:
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EFFICACY OF THREE BT FORMULATIONS ON CABBAGE LOOPER AND DIAMONDBACK MOTH ON CABBAGE IN THE LOWER RIO GRANDE VALLEY, TEXAS, 1997-1998. This trial was conducted at the Texas Agricultural Research and Extension Center at Weslaco. Cabbage were established in 2-row x 30 ft long plots on 15 Sep, 1997. Each treatment plot consisted of a single row of cabbage plants at 1-ft spacing. Treatment plots were separated with sorghum wind breaks and a 5 ft alleyway. All treatments were arranged in a RCB design with four replications. Fertilization consisted of 100 lb/acre of N-32 at planting, 50 lb/acre on 30 Oct and 26 Nov 1997, respectively. The herbicide, Prefar 4E was used at 6 qt/acre at planting (15 Sep). The plants were sprayed twice with the fungicide Bravo-750 at 1 qt/acre on 24 and 31/Oct, respectively. Plants were scouted on a weekly basis and insecticide application was made as threshold levels exceeded 0.3 larvae/plant. Three Bt formulations, Dipel DF, ABG-6492 and ABG-6405 were used, and untreated plants served as checks. The materials were applied using a tractor-drawn sprayer with 3 nozzles per row at 100 psi at a delivery rate of 30 gpa. Spray was initiated on 23, 30 Oct, 6, 14, and 25 Nov. Sampling was initiated 4 wks after planting. Number of small, and large larvae per plant was counted by checking both the upper and lower surfaces of every leaf for 10 plants from each plot. At termination, a damage/quality evaluation was made on 10 plants per plot based on the following 6 categories: 0-no damage, 1-minor feeding damage (1% eaten), 2-minor-moderate feeding damage (2-5% eaten), 3-moderate damage (6-10% eaten), 4-moderate-heavy damage (1130% eaten), and 5-heavy damage (>30% eaten). Numbers of larvae per plot were subjected to ANOVA, and means were separated using the LSD test at P = 0.05 (SAS Institute 1996).
The pressures of both cabbage looper and diamondback moth were high, but there were more cabbage looper than diamondback moth. The five Bt insecticides significantly reduced the larval population of cabbage cooper and diamondback moth. All materials were effective against diamondback moth, and to larval population was reduced below the economic threshold after five applications. All materials, however, were not very effective against cabbage looper larvae, and the larval population was above the economic threshold after five applications. No phytotoxicity was observed.
