Pros and Cons of Soil Insecticide Use for Corn Rootworm Protection

11:52AM Apr 17, 2014
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Entomologists say root protection from single traits that are working well will not increase when an insecticide is added on top of the trait.

Should you use a soil insecticide at planting this season to protect your corn against corn rootworm pressure?

It depends, according to university entomologists.

"We have shown in our field trials that an insecticide on top of a single trait only improves relative root protection if the single trait is starting to fail in the field," notes Lance Meinke, University of Nebraska-Lincoln entomologist. "In this case, root protection improves but selection for resistance to the trait continues, so this is not a good long-term solution to the problem.

"Root protection from single traits that work well will not increase when insecticide is added on top of the trait," he says. "Also, we have not seen an increase in root protection when an insecticide is added on top of a pyramid containing Cry34/35Ab1. So in most cases, we do not recommend using a soil insecticide on top of a pyramid that contains Cry34/35Ab1."

If you plant a pyramided corn hybrid with multiple Bt events to protect your crop from rootworm larvae, the chance of an economic return-on-investment is unlikely when using a soil applied insecticide, adds Mike Gray, University of Illinois Extension entomologist.

However, another consideration is how much damage is your corn crop likely to experience this season from other pests such as grubs, wireworms and seed corn maggots, asks Mike Hancock, corn segment manager for FMC Corporation, which manufactures Capture LFR.

"There are a variety of pests waiting to attack that seed as soon as you close the furrow that an insecticide put down at planting can protect your crop against," he says. "An in-furrow treatment can help you increase your stand count and protect yield potential through the life of the crop."

As for rootworm management, the issue continues to be a major concern for farmers across much of the Midwest. Earlier this year, a webinar "Corn Rootworm Management in the Transgenic Era" was presented by five land grant entomologists. During the program, the entomologists detail rootworm management challenges and recommendations for 2014. The webinar was supported by a USDA-NIFA North Central IPM Program grant. The recording can be watched at the North Central IPM Center homepage at this link: