CHAMPAIGN, Ill. — Resistance, the old enemy to good pest control, seems to be rearing its ugly head again when it comes to corn rootworm.
The Bt traits released in 2003 have been of tremendous value, but both northern and western corn rootworm are a problem again this year in Nebraska and Iowa, said Joseph Spencer, principal research scientist in insect behavior at the University of Illinois Urbana-Champaign.
Part of the problem is overuse of “the goose that laid the golden egg,” he told farmers and crop advisors at Agronomy Day in Champaign Aug. 19.
Some advisors in northern Illinois told him they are seeing more corn rootworm again this year, and more apparent resistance to Bt traits.
This year, central and eastern Illinois don’t seem to have a problem with corn rootworm, he said, based on his research and closely monitoring numbers. There have been lower populations here in recent years.
As always, rotation is recommended as a way of reducing corn rootworm, he said. Surveys and research showed the resistance varies to the products and in different areas.
Spencer recommends scouting early. Plants damaged by corn rootworm may appear to be wilting and have a tendency to fall over in rain and wind due to a shallow root system. Chewed leaves and silks may also be a sign of adult beetles.
The entomologist recommended monitoring crops.
“It is important to only use Bt when it is needed. It is important to preserve the traits,” he said.
Decisions should be made with a “field to field” approach using different management options as needed.
Bt is a great tool, but it shouldn’t be the only one. Sometimes, it is a better answer to use soil insecticides, Spencer said. If the populations are large, don’t use Bt because the resistance may show that it isn’t working.
“Be careful how we use these products, we don’t want to use them up,” he said.
As the same time, innovative research continues here as well as in Nebraska and Iowa on nematodes that might help manage the beetles, he said.
No one wants to go back to 1995 when the corn rootworm situation was very difficult, Spencer said.
“We are shooting all the arrows we have in our quiver,” he said.