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In addition to increasing corn yields and cutting nitrogen expense, keeping soybeans in the rotation lowers next year’s corn rootworm management costs, says Ken Ostlie, University of Minnesota Extension entomologist. “Rotation resets the population of corn rootworms in a field, so you can get by with fewer rootworm inputs the next year. You can eliminate insecticide use, or plant all non-Bt corn that first year.”
Keith Schrader, farmer from Nerstrand, Minn., has learned he must rotate to soybeans for long-term rootworm control, since he’s had resistant rootworms on continuous-corn acres.
The Schrader family’s best corn field has a high-tech problem. Fortunately, there’s a low-tech solution: crop rotation.
Corn rootworms in this longtime continuous-corn field seem to have become immune to the Cry3Bb1 trait, the most common source of transgenic rootworm protection, says Keith Schrader, who farms with his sons near Nerstrand, Minn. In 2011, YieldGard VT Triple knocked out just 25% of corn rootworms in this field, compared to an expected kill rate of more than 95% in fields where the trait works, says Ken Ostlie, University of Minnesota Extension entomologist.
Due to a rental agreement, this field remains in continuous corn, but to achieve long-term rootworm control, “We’re going to have to rotate to soybeans,” Schrader says. Ostlie agrees: “Rotation would totally solve this problem.”
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Pest management is the main reason the Schraders keep soybeans in the lineup on their 3,700-acre operation. Even though crop prices and relative yields often favor corn-after-corn, soybeans offer valuable benefits, Schrader says. Along with better pest management, beans in the rotation let growers:
•diversify weed-control chemistry and cut resistance risk
•save on N, fuel and labor
•spread out fieldwork
•increase corn yields
A soybean-corn rotation “is a good risk-management strategy for both crops,” says Shawn Conley, University of Wisconsin Extension soybean agronomist. Corn yields are 13% to 19% higher after soybeans, according to 30 years of University of Wisconsin trials. Input costs are lower, and in weather stress years, soybeans and rotated corn are more resilient than continuous corn.
Joel Schreurs follows a two-year, corn-soybean rotation on about 80% of his 1,000-acre operation near Tyler, Minn. “It breaks the cycle of diseases, insects and weeds, and gives you more avenues of crop protection. That’s the biggest value for me.”
Rotation is still the best way to control corn rootworms in most of the Corn Belt, says Tristan Mueller, operations manager for the Iowa Soybean Association’s On-Farm Network. “One year of soybeans will knock out CRW populations.” After that, Ostlie adds, you may only need to plant soybeans every few years to keep them in check.