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Midwest food processors are well positioned to avoid major crop losses, and product contamination resulting from pyrethroid resistance in corn earworm (CEW), Helicoverpa zea (Boddie). However, we do recognize risks associated with late-season plantings, particularly for sweet corn and snap beans. CEW usually migrate into the production areas by late July to mid-August. Crops at risk for most Midwest locations primarily include sweet corn planted after 10 June and snap beans planted after 10 July (about 25% of the Midwest acreage). Pyrethroid insecticides continue to be the commercial standard, with alternative chemistries either ineffective or more expensive. The CEW "treatment window" for sweet corn is from row tassel to dark brown silk and, for snap beans, from bloom to 10 days before harvest. In sweet corn, CEW is only vulnerable as an adult, egg, or early instar feeding on the silk. If left untreated, or with insecticide failure, we anticipate a loss of about one square inch of kernels per larva (2 cases/ton of final cut-corn product). The loss of kernels and the creation of black kernels from contamination associated with feeding injury are estimated to have a market cost in excess of $100/acre, or $6 million for Midwest sweet corn and snap beans. We currently have no effective alternative insecticides for CEW for either crop. In the short term, processors will likely use higher rates of pyrethroids, shorter intervals, and/or additional treatments. Long term, we will increasingly rely on a "process-out" approach to husk out, wash out, and vision-sort larval contaminants and damaged kernels. Introduction Pyrethroids are the commercial standard for control of corn earworm (CEW), Helicoverpa zea (Boddie), in sweet corn and snap beans in the Midwestern US (12). The broad spectrum of control, reduced active ingredient per acre, economical price, and high efficacy against CEW and other pests resulted in their rapid adoption and use since the late 1980s (5,6,8). However, since 2001, reports of CEW pyrethroid resistance in small-plot research trials have become common (8). To date, commercial growers of sweet corn and snap beans in the Midwest have not experienced crop failure as a result of resistance issues, but have had to make adjustments in rates and timing to match fluctuating pest populations. Unfortunately, alternative insecticides currently available have not demonstrated better control and are significantly more expensive (12). Most CEW that migrate to the sweet corn and snap bean processing areas of the Midwestern US (north of 42°N latitude) either do not have time to complete pupation to facilitate adult emergence or are not known to survive the winter at these latitudes (9). Thus, pest management activities in the northern Midwestern states will likely have little impact on the CEW levels of resistance. Light-trap data for some southern locations in the Midwest do indicate the possibility of reverse migrations in the fall (Flood, unpublished), but the extent and significance has not been determined. Symposium: Increasing Concerns about H. zea Susceptibility to Pyrethroids in the Midwestern USA 19 July 2007 Plant Health Progress In this paper, we develop a plan to manage CEW in the Midwestern US by reviewing CEW migration patterns and the use of the "treatment window" within an integrated pest management (IPM) context (2,5). We also discuss options currently available to manage CEW and pest damage on processing crops. Corn Earworm Migration and Management State departments of agriculture, university personnel, and the Midwest Food Processors Association have a long-term cooperative monitoring network for CEW and other moth pests. Network data are summarized graphically on the VegEdge website [www.vegedge.umn.edu (7)], and are also distributed via the Minnesota Fruit and Vegetable Newsletter (7). The system aids in disseminating CEW flight activity at several locations in the Midwestern US, but currently lacks a national scope. Several vegetable insect pests in the Midwest region annually migrate to vegetable crops, including CEW (5). The first edition of the book Vegetable Insect Management (4), published before the introduction of genetically modified (GM) field crops, recapped decades of pheromone and black light trap data as indicators of migration patterns and re-infestation potentials for CEW and other pests. Treatment frequency and insecticide rates were adjusted to the nightly trap catch results. The IPM programs discussed in the book are still valid. However, the second edition of this book (5) highlighted the impact of GM field crops on ECB populations — specifically, an apparent region-wide suppression effect in several Midwest states (2). GM crop impacts on CEW were not highlighted in the book (5). Some recent trends are reviewed here. Corn earworm trap catch results from 1958 to 2006 have been annually consistent with respect to timing of occurrence (2). However, when the top 12 CEW Midwest migration events (highest moth catch densities) in the 58-year data base were examined, none of these events occurred after 1985 (10). Pyrethroid insecticides were introduced to southern field crops during this period and, since the southern US is considered the primary source area for Midwest CEW immigrants, the improved control of CEW in the South could be partially responsible for the reduced flights into the Midwest. Moreover, since 1996, the introduction and high adoption rates for GM cotton transformed to express various Bacillus thuringiensis (Bt) proteins toxic to CEW has significantly reduced CEW flights in some southern states, including Mississippi (1). Although most Bt cotton to date (e.g., Bollgard I) is not known to provide complete control of CEW, the use of Bt cotton on about 45 to 70% of the southern cotton acreage as of 2005 (depending upon the state) may have also contributed to reduced regional source populations (1). That said, CEW infestations in other southern crops (e.g., field corn, sorghum, and soybean) result in continued pyrethroid use and selection pressure (11). The potential loss of pyrethroids as a large-area population suppression tool in the South, given a current lack of alternatives, could create larger, more damaging populations in

Potential Impact of Pyrethroid Resistance in Helicoverpa zea to the Midwest Processing Industry: Sweet Corn and Snap Beans