ABSTRACT

Widestrike (MXB-13), VIP (COT-102), and Bollgard II (DP-468 BGII) cotton lines were compared for their efficacy against the cotton bollwormy, Helicoverpa zea (Boddie), in northeastern North Carolina under high bollworm pressure- an extended bollworm moth flight, irrigation, and a beneficial insect-disruptive application of Orthene just prior to bollworm establishment. Because Monsanto regulations currently prohibit the direct comparison these new Bt cottons (adjacent to one another in the same test), each different technology was evaluated in separate, but adjacent tests within the same field border. The Widestrike, VIP, and the Bollgard II lines showed bollworm damage to bolls of 15, 14, and 6%, respectively at the mid September peak boll damage scouting assessment. Additionally, the VIP cotton line sustained 2% European corn borer damage to bolls. Yield differences appeared to follow these boll damage trends, with the pyrethroid-protected counterparts of these same lines showing yield increases for the Widestrike, VIP and Bollgard II lines of 141, 292, and 185 lb. of lint/acre, respectively. These yield differences appeared to have been caused by bollworms- stink bug levels were extremely low at this location, and an early application of Centric was made to the entire test area on August 1 for a low level of plant bugs. It should be noted that the Bollgard II test may have benefitted somewhat from an earlier planting date. Although Bollgard II would seem to be the "gold standard" for bollworm control, the efficacy of both Widestrike and VIP COT 102 was higher than adjacent Bollgard cotton. Additionally, VIP cotton lines (COT 200 series) with more bollworm-active gene promoters are presently being evaluated. Widestrike, VIP and Bollgard II cultivars, with their greater bollworm activity, should further lower the insecticide use for this species in Bt cotton. With late season insecticide use in North Carolina presently averaging less than a single application from 1996 to 2002 (Bacheler and Mott 2002), a further lowering of this usage pattern will not likely have as dramatic an impact on increased plant and stink bug levels as in other areas of higher insecticide use in Bollgard cotton.