Concern for corn rootworm control continues to rise among farmers throughout the Midwest. The continued use of the same rootworm resistant Bt trait in corn hybrids, coupled with the lack of required refuge acres, has caused rootworm resistance to become a real issue.
Mark Grundmeier, product manager for Latham Hi-Tech Seeds says managing corn rootworm has become increasingly important as the number of corn-on-corn (c-on-c) acres rises. "Rotation is key, more specifically - trait rotation. If rootworms cannot be managed by rotating traits, rotate to other crops (like soybean or alfalfa)," he says. "In addition to rotating traits, you can further minimize your risk by planting various corn maturities."
It's important to note not all traited products offer rootworm protection, Grundmeier says. "Herculex I, for example, has resistance/tolerance to Liberty, Roundup (some hybrids) and corn borer," he says. "However, it does not protect against corn rootworm. A person can't just assume that a Bt hybrid will have rootworm protection."
If you are planting corn-following-corn, rootworm control is definitely needed
If planting corn following corn – rootworm control is a must, he adds. "You'll see extended diapause (from Northern Rootworm) in ground that has been rotated. In an area with heavy rootworm pressure, look at dual modes of action and consider rotating crops in areas where rootworm pressure is extreme."
University research data confirms the real strategy for dealing with high corn rootworm pressure is to use rootworm-traited genetics. Additionally, the use of hybrids with more than one rootworm trait (e.g., SmartStax) may need to be used. Grundmeier adds, "Refuge acres must be planted, and Refuge-In-the-Bag (RIB) hybrids make compliance simple. By respecting refuge, we can greatly increase the likelihood of keeping rootworm traits viable for years to come."
Volunteer corn creates "safe harbor" for rootworm; control the volunteer corn
Nick Benson, corn product specialist for Latham Hi-Tech Seeds urges farmers to treat volunteer corn like weeds because the volunteer corn actually serves as a "safe harbor" for corn rootworm. Corn rootworms essentially need corn to survive, he says. That's why a corn-soybean rotation has been an effective control measure. However, when corn appears in a bean field, the rootworm larvae have a food source, and will ultimately attract corn rootworm beetles for egg laying.~~~PAGE_BREAK_HERE~~~
"Most eggs are laid in the upper 6 inches of soil during late summer and the eggs remain dormant until the following spring, so they're ready to feast on the next crop of corn," Benson says. He recommends applying a tank mix treatment to clean up volunteer corn to help avoid the soybean variant in the Western corn rootworm beetle.
In general, with careful crop planning and herbicide use, volunteer corn can be controlled in both corn and soybeans, says Grundmeier. Several herbicides (e.g., Select, Fusion, Poast Plus, etc.) will take care of volunteer corn in soybean fields, but persistence is key as more than one application may be needed.
Volunteer corn in continuous corn situations can be managed by careful planning
Volunteer corn in continuous corn situations can be managed by understanding the herbicide tolerances of the traits involved. For example, Grundmeier notes most Monsanto-traited hybrids contain only the glyphosate-resistant trait for herbicide use. If you plant corn following one of those hybrids, choose a hybrid that incorporates the LibertyLink trait. If you plan to have many years of continuous corn, stay away from hybrids that contain both the LibertyLink and the glyphosate gene for herbicide resistance. Rotating to soybeans or alfalfa can also help break that cycle.
"The bottom line -- higher numbers of volunteer corn can build higher corn rootworm populations for the next growing season," says Grundmeier. "Higher rootworm numbers are especially problematic when those fields are planted to corn the following year in a corn-soybean rotation or in continuous corn." Visit Latham Hi-Tech Seeds website or blog for more information.