CHAMPAIGN, Ill. — As the toxins from Bt corn become less and less effective at managing western and northern corn rootworms, what’s next? It will take a combination of innovative techniques to provide sustainable control, according to University of Illinois researchers, who are gearing up for a project involving next year’s crops.
Joseph Spencer, insect behaviorist at the Illinois Natural History Survey, and Nick Seiter, field crop entomologist in the U of I Department of Crop Sciences, will begin a four-year project on soybean-Bt corn rotated crops in spring 2022 to evaluate the effectiveness of alternate methods combined with Bt corn in rotated crop fields.
They plan to use drones to monitor rootworm beetle populations, apply entomopathogenic nematodes to prey on corn rootworm larvae and plant cover crops in experimental fields that have significant corn rootworm abundances.
“Preliminary data suggest these techniques can enhance protection for corn from rootworm larvae and improve the overall system,” Spencer said. “We’re recognizing the best way to control corn rootworms is to combine a variety of methods to achieve more sustainable management. We can’t rely just on treated corn to deal with corn rootworms.”
The scientists are looking for growers from northwest, central or east-central Illinois and from northwest Indiana to participate in the project comprising two cycles of soybean-corn rotation, starting with soybeans in 2022.
The main participation criteria include a history or yearly expectation of moderate to heavy larval corn rootworm pressure and fields with long histories of Bt use.
By monitoring corn rootworm populations in soybean fields in the first year of the project, the researchers and growers can measure the anticipated corn rootworm pressure in those fields when they are rotated to corn, Seiter said.
Sticky traps will be placed on PVC poles in soybean fields. Typically, the number of adult beetles on each trap is counted once a week for four weeks.
Instead, drones will be flown over the field to take pictures of the sticky traps. In this aspect of the project, scientists will quantify the economics of drone monitoring and compare it with standard in-person monitoring.
Drones save time spent walking the fields in the summer heat, while collecting the same amount of data. Wading out into the soybean field to visit the traps is considered such a hassle by some, that growers often avoid or limit regular pest monitoring.
In addition, a part of the field will be treated with a mixture of nematodes, which prey on corn rootworm larvae and other soil-dwelling pests, to be applied once during the fall of year one or in spring of year two. Soil tests will determine if the nematodes are persisting year after year following one application.
“The same mixtures of entomopathogenic nematodes have been applied widely in the Corn Belt with promising results,” Spencer said.
Growers will also select a cover crop to plant on part of the field to see if this influences corn rootworm behavior, if the treatment is economically feasible, and to measure the effects on soil health.
Cover crops are a key part of the Illinois Nutrient Loss Reduction strategy and have the potential to enhance populations of natural enemies that attack corn rootworm, according to Seiter.
Growers say they are open to new methods, but these must be practical for the farm.
“Any new ideas for this old problem ultimately have to be economical,” Spencer said. “Growers are looking for new ways to help them to be better stewards of the land and improve profitability.”
Through the study, the researchers hope to monitor corn rootworm abundance trends to provide better management recommendations to Illinois farmers and observe regional changes in corn rootworm populations.
The project, funded by Corteva Agriscience, is also underway in Iowa and Nebraska. Christian Krupke at Purdue is a collaborator in Indiana.