Corn farmers in southeastern Virginia are busy scouting for second generation egg masses of the European corn borer this summer. A heavier-than-usual first generation infestation of the European corn borer has been causing concern in the area and could mean up to a 30 percent reduction in corn yields in some southeast Virginia fields this year.
For the past two years, ECB caused some damage to Bt cotton and cotton seedlings.
ECB tends to go in cycles, so entomologists are looking toward next year with a wary eye. “For Virginia, first-generation infestations are pretty light year-in and year-out,” says Rod Youngman, Virginia Tech professor of entomology and Extension specialist. “We usually don't consider it a big pest, but this year's infestation is different. It's not a classic, regional infestation, for example, where 70 percent of the corn in every county is infested.”
However, reports from county agents in Virginia have seen anything from lightly-infested to pocks of heavily-infested fields.
Charles City and Isle of Wight counties are two of the more heavily ECB-infested areas of the state, Youngman says.
The European corn borer over-winters in the late larvae stage; the moths lay eggs on the undersides of corn leaves in mid-May. Once the eggs hatch, the young larvae work their way down the plant and begin chewing into the whorl or stalk.
Plants are typically susceptible to corn borer feeding after the fifth- or sixth-leaf stage, Youngman says. Before becoming an adult insect, ECB cycles through five instar stages.
“Research has shown that there's about a 5 percent yield loss for every corn borer in whorl-stage corn,” Youngman says. “For example, if you have three worms per plant, you can expect about a 15-percent loss.”
Given the current height of corn now in eastern Virginia, farmers have few options available in applying insecticides for second-generation corn borers. Insecticides must be applied over-head to the plants for maximum control. This is best accomplished by overhead irrigation systems or by aircraft.
However, Youngman noted, aerial application of insecticide is not widely practiced in Virginia. “It's not necessarily given that the first generation will automatically lead to a serious second generation.”
Youngman recommends monitoring in mid- to late-August for ECB damage and consider harvesting early if grain moisture levels are acceptable.
In corn, ECB can be controlled with insecticides. However, scouting is necessary to properly time insecticide applications. “Few farmers in Virginia have the capability to treat second-generation corn borers because by mid-July the height of the corn plant usually restricts access,” Youngman says.
Historically, there has not been enough ECB pressure to warrant large-scale planting of Bt corn varieties.
In light of the increased pressure, entomologists are advising farmers to consider planting Bt corn hybrids next year in fields, which they feel are greatest risk to ECB. “We could see an increase in the planting of Bt corn next year based on this heightened pressure,” says Ames Herbert, Virginia Tech Extension entomologist.
Bt corn requires a 20 percent non-transgenic resistant management requirement and could provide an opportunity for side-by-side comparisons, Youngman says.
Youngman is also conducting research in the western part of Virginia to determine whether growers could benefit from Bt corn that's grown for silage.
Meanwhile, there's the ECB pressure in cotton.
Herbert says this is the second year that cotton seedlings have been affected by the pest. So far, it hasn't caused economic pressure, but has been enough to get the attention of farmers.
“Last year, ECB did stem and stalk damage in Bollgard fields,” Herbert says. “ECB moved from weeds in the middle of the rows and developed on cotton. We're told that they cannot start in cotton from egg masses the way they do in corn. In cotton, they're moving laterally after getting a start on something else.”
The only real threat to cotton, Herbert says, would be boll damage late in the season after the bollworm sprays have worn off. “When we spray for bollworms, we're going to take it out, but where we drop our guard or quit looking, it could be a concern,” Herbert says.