DOT Project Number:  90-00-LRTF-713

Fiscal Year:  1997

Award:  $1,250.00

Principal Investigator:  Dr. John M. Pleasants, Iowa State University, jpleasan@iastate.edu

Summary Report:

LARVAL INFESTATION IN CORN NEAR VARIOUS VEGETATION TYPES

We investigated whether a greater abundance of European Corn Borer (ECB) adult moths in the vegetation bordering a corn field led to greater egg laying in that field resulting in a higher ECB larval infestation in that field. We compared levels of infestation of second-generation ECB larvae of corn growing near borders of brome, prairie, mixtures of prairie with weeds or brome, and foxtail. Infestation levels were sampled at progressive distances along several transects from the edge of the field up to 25m in the interior. A total of 3120 stalks in 26 transects were examined at three sites.

At one site there were fewer larvae near prairie than near brome. At the second site there were fewer larvae near prairie and near foxtail than near brome. At the third site there were no strong significant differences in infestation levels of corn near brome, prairie and foxtail. At sites where significant differences did exist, they typically disappeared at 25m.

Several tentative conclusions can be drawn from this data. First, any effect due to border vegetation is an edge effect; border vegetation does not affect infestation levels beyond 25m into a field. Second, the size of the border may influence whether it has an effect. The first two study sites, which had large tracts of different border vegetation, did show significant effects whereas the third site, which had small tracts, did not. This is probably related to the ability of moths to fly up to 100m from their aggregation site to oviposit. Third, the number of moths aggregating in a particular type of border vegetation was not always related to infestation level. In particular, foxtail, which had the highest moth abundance, did not have the highest infestation level. Fourth, there is no indication that prairie plantings along roadsides would increase infestation levels in adjacent cornfields; if anything, the data suggests that infestation levels would be reduced compared to brome. Fifth, the study focused on second-generation ECB infestations. First generation corn borers do the most damage to corn plants. Although we did not look at first generation corn borer damage, we suspect that this would be much reduced if brome grass roadside strips were replaced with prairie strips because brome grass is highly preferred as an adult aggregation site in the first generation.