- Agronomic: corn
- Crop Production: conservation tillage
- Education and Training: extension, farmer to farmer, on-farm/ranch research
- Farm Business Management: budgets/cost and returns
- Pest Management: biorational pesticides, cultural control, economic threshold, field monitoring/scouting, integrated pest management
- Production Systems: agroecosystems, transitioning to organic
European corn borer infestation level had a significant negative effect on whole-plant yield (P = 0.0086), whereas the main effect of plant growth stage as well as the interaction between plant growth stage and infestation level had no significant effect on whole-plant yield. Of the five infestation levels, only the infestation level of 5 larvae per plant resulted in a significantly lower whole-plant yield (282.3 ± 10.8 g/plant) than the uninfested control (315.3 ± 7.5 g/plant). Economic injury levels are presented for each of the growth stages, where significant regressions were found between whole-plant yield and infestation level. In addition, plant growth stage and infestation level had no effect on percent acid detergent fiber, percent neutral detergent fiber, and percent crude protein values.
Field corn is one of the most important crops grown for grain and silage worldwide (Youngman and Tiwari 2004). The U.S. accounts for nearly one-fifth of annual worldwide corn production and ranks as the number one corn-growing nation in the world (Youngman and Tiwari 2004). In 2001, Virginia corn farmers harvested 133,550 hectares of grain and 54,630 hectares of silage, which yielded over 40.5 million bushels of grain and nearly 2.1 million tons of silage.
European corn borer has posed a potential risk to corn farmers in the Mid-Atlantic and southeastern U.S. for decades. However, most farmers have elected not to aggressively control this pest because of years of infrequent and sporadic infestations, and the cost and effort associated with traditionally managing this insect. Biological control has been investigated for managing European corn borer on field corn, but it has yet to prove economically successful in North America (Youngman and Tiwari 2004).
Essentially, the traditional way of managing second generation European corn borer infestations has consisted of aerially-applying granular insecticides on cornfields identified with above threshold eggmass counts. Although the traditional method has been proven to be cost effective on corn grown for grain, it is not considered an economically viable option in many areas where corn is grown for silage (Thompson and White 1977, Myers and Wedberg 1999). Now, the simple convenience of planting Bt corn hybrids that impede European corn borer feeding injury has dramatically changed the pest management scenario for this insect. Although planting Bt corn seed is straightforward, the main drawback is that it is not possible to predict at the time of planting whether a field will sustain enough European corn borer pressure to benefit from the additional cost of $17-25 per ha for the Bt corn seed (Hyde et al. 1999).
Surveys conducted by Youngman et al. (1998, 1999, 2000), and Youngman and Laub (2002) on second generation European corn borer damage in conventional (i.e., non-Bt) cornfields in eastern (1997-99) and western Virginia (2000-02) have provided partial insight on the role for Bt corn in Virginia. Less than 2 percent of the 172 fields surveyed annually in eastern Virginia from 1997-1999 experienced economic damage from European corn borer. The western Virginia survey findings, however, revealed a different picture (Youngman and Laub 2002). Nearly 25 percent of the 126 fields surveyed annually from 2000-2002 experienced economic damage. For the fields in these surveys, economic damage was based on a threshold of 1 or more tunnels of > 1.3 cm in length per plant. It is important to realize, however, that this economic threshold was developed on corn grown for grain; not corn grown for silage. The significance of this is that this threshold can be applied with confidence to the eastern survey results because the vast majority (> 90 percent) of corn grown in eastern Virginia is grown for grain. In contrast, the majority of corn grown in the western half of the state is largely grown for silage and kept on-farm as feed for dairy animals. Therefore, it was important that research be done to determine the level at which European corn borer causes economic damage in corn grown for silage. This study has improved our understanding on the appropriate role for Bt corn hybrids in managing European corn borer populations in fields planted for silage production.
Objective 1. Determine effects of European corn borer infestation on whole-plant yield and forage quality of corn grown for silage
Objective 2. Determine economic injury levels of European corn borer infestations at the 10-leaf, 16-leaf, and blister stages of corn grown for silage