Sweet corn is a high-value crop important to the agricultural economy of the northeastern and midwestern United States. In 2007, there were about 324,000 acres of sweet corn grown in this region, and the value was about $1186 per acre (U.S. Department of Agriculture, 2008). Because of this high value, and because consumer tolerance for insect infestation is typically very low, sweet corn production can require high insecticide and labor inputs (Dively, 1996; Flood et al., 1995) to prevent harvest infestation and damage by european corn borer, corn earworm (Helicoverpa zea), and fall armyworm (Spodoptera frugiperda).
Producers of fresh market sweet corn plant on a succession of dates to provide a continuous supply of produce for the market throughout the growing season (Ferro and Fletcher-Howell, 1985), resulting in a wide range of harvest dates. The practice of planting sweet corn in a succession of plantings (“staggered plantings”) is also used in processing sweet corn production to meet demand (Pike, 2003). These staggered planting and harvest dates, plus large seasonal variation in european corn borer seasonal activity, lead to large variability in european corn borer infestation levels. During periods of high european corn borer infestations, recommendations suggest the application of an insecticide every 4 days during the “silking” stages to prevent ear damage (Dively, 1996). This can result in three to five insecticide applications per planting to control this pest. Conversely, these recommendations also suggest that no spray is needed when insect populations, as indicated by egg density or moth catches in traps, are sufficiently low.
Studies have shown that european corn borer infestation in the ear and damage at harvest in sweet corn varies somewhat predictably according to harvest date. Ferro and Fletcher-Howell (1985) found a bimodal pattern of infestation levels, with plots harvested before 1 Aug. having moderate european corn borer infestations, the plot harvested on 4 Aug. having almost no infestation, whereas those harvested after 10 Aug. and into September had much higher infestation levels. Andreadis (1988) also found similar results in Connecticut, with low infestations found on a 12 Aug. harvest date, and much higher infestations in September and October harvests. These studies indicated infestation patterns caused by the bivoltine ecotype (Mason et al., 1996) of european corn borer.
Temporal patterns of european corn borer larval infestations have shown somewhat different patterns where the univoltine ecotype and bivoltine ecotypes are present, such as in New York. For instance, Shelton (1986) examined european corn borer damage for processing sweet corn in New York. In 1983, he found that european corn borer damage was consistently higher in August than in September. In contrast, in 1982 infestations were higher in September compared with August. These observations may have indicated that infestations occurred from univoltine (which occur from late July to late August) and second-generation bivoltine european corn borer larvae (which occur from mid-August into September). Mixes of both voltine ecotypes have been documented in New York (Eckenrode et al., 1983).
There are various approaches to monitoring and predicting european corn borer infestation in sweet corn. European corn borer is relatively easy to monitor in its egg, larval, or moth stages, thereby facilitating in-season management programs that can be used to evaluate the risk of crop infestation (Dively, 1996; Flood et al., 1995). Egg mass scouting can be made more efficient with the use of larval stage-structure models, which optimize the timing of in-field egg scouting programs (Calvin et al., 1986). Simpler degree-day models have also been used that predict peak activity of moth flights based on degree-day accumulation (Despins and Roberts, 1984), and development rates based on degree-days can be used to predict occurrence of various life stages of european corn borer (Bessin, 2003; Glogoza and Boetel, 2005; Tollefson and Calvin, 1994). Finally, current monitoring results, historical records, and predictive aspects can be integrated for practitioners to readily access and use (Fleischer, 2003; Holmstrom et al., 2001; Hutchison and Wold, 2003).
These approaches use growing-season activities to monitor and predict the occurrence of european corn borer in sweet corn at harvest. However, no systematic attempt has been made to predict the risk of harvest infestation by european corn borer at the time of planting. Development of an at-planting prediction system would increase the ability of growers to anticipate harvest infestation, and, therefore, needed management resources (i.e., scouting, labor, insecticides, biological control, and extra cost of transgenic sweet corn) at planting time. Integration of degree-day models that predict harvest date based on corn development (Arnold, 1974; Ritchie et al., 1992), predictions of european corn borer stages present at the time of harvest (Bessin, 2003; Glogoza and Boetel, 2005; Tollefson and Calvin, 1994), and use of landscape prediction techniques (Royer et al., 1989) could improve management of european corn borer in sweet corn.
The goal of this research was to develop a prediction system of sweet corn ear infestation risk by european corn borer larvae for various planting and harvest dates by integrating european corn borer and sweet corn developmental rates. Using documented european corn borer infestation levels across a range of harvest dates from central Pennsylvania, these infestation levels and harvest dates were related to sweet corn developmental rates. Using this information, a method is proposed to assess the risk of european corn borer harvest infestation for an individual site and across a landscape at planting time.
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