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Pick where to control rootworm

Suppose your budget said “no” to planting all triple-stack hybrids. They include the Bt trait for rootworm control. If you still opted for some Bt rootworm corn, where should you plant it?

That’s the lead question for the panel of Indiana Certified Crop Advisers. See if their advice fits with the strategy you believe works best on your farm.

Panel members include Jesse Grogan, with LG Seeds, Lafayette; and Dan Ritter, Newton County Extension ag educator.

I ordered enough GMO-rootworm corn for 300 acres. Should I plant it on corn after beans, or save it for continuous corn? We didn’t trap for beetles in soybean fields. We live in central Indiana. Where I don’t plant it, should I use an insecticide, or just hope there isn’t a problem?

Key Points

• Your location in the state plays a big role in rootworm control decisions.

• Scouting would have let you monitor rootworm beetles in soybeans.

• Consider other insects to control, suitability of hybrid to continuous corn.

GROGAN: Planting GMO-rootworm corn would have an advantage in corn following soybeans. Rootworm pressure has been higher for corn following soybeans in rotation in central Indiana, compared to the past.

Rootworm pressure can also be high in corn after corn. It’s essential to select the best hybrid for corn after corn that also includes the rootworm trait.

Sampling rootworm adults in soybeans in the year prior to corn planting is important to determine the need for control on a field-by-field basis. Fewer adult beetles were observed last year since cool, wet spring weather contributed to larval mortality.

Yield of Bt rootworm corn has been found to be consistently higher when compared to yield of refuge corn in the same field for most of central Indiana.

Seed-applied or soil insecticides applied with planter boxes can make a difference on refuge acres. Usually control is better with soil-applied insecticides.

RITTER: The short answer would be plant it on corn-after-corn acres. That would be your greatest chance for corn rootworm infestations.

Since you’re in central Indiana, first-year or variant corn rootworm beetles may not be as prevalent as in other locations. So the option may exist to use no insecticide on your corn after soybean acres.

That’s not the case in northwest Indiana. The first-year variant beetle that lays eggs in soybeans is very prevalent there. You would likely want protection in that part of the state. Finding corn rootworm larvae is rare, however, in corn after soybeans in much of the southern third of Indiana.

Keep in mind that there may be other pest problems you need to manage for with an insecticide. Also, consider the agronomic fit of your hybrid when deciding where to plant. There may be differences in how hybrids react in continuous corn situations.


TOUGH CUSTOMER: Assess your odds of finding rootworm larva like this one in various fields.

John Obermeyer, Purdue University Entomology Dept.




This article published in the March, 2010 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.