Soil Insecticide Surge

March 8, 2013 08:15 PM
Soil Insecticide Surge

Treated corn acres will increase at least 40% this year

Fifteen years ago a little-known version of the western corn rootworm, called the soybean variant, showed up in Jim Brown’s corn crop with a big appetite.

"It was pretty devastating to yields that first year because I had no idea it was there," Brown recalls.

Unlike typical rootworms that lay their eggs in corn, the soybean variant flies into soybean fields to lay its eggs. This allows the larvae to hatch the following spring in a field likely planted to corn. That means a standard corn-soybean rotation is unable to keep the pest in check, which was Brown’s case. He turned to granular soil insecticides for help and has used them ever since.

This spring, Brown can expect a lot of company from like-minded farmers. Acres treated with soil insecticide are projected to reach 15 million, a 40% increase from 2012, according to Joe Short, Midwest marketing manager for Amvac Chemical Corp.

The surge in soil insecticide use is an about-face for farmers; usage reached an all-time low in 2006. Short attributes the shift to more continuous corn acres, control breaks in corn rootworm single-trait hybrids and growing challenges from secondary insect pests.

Short reports that the largest increases in soil insecticide use are concentrated in Iowa, southern Minnesota, parts of Nebraska and northern Illinois, where continuous corn production systems are common.

More options needed. Ron Hammond, Ohio State University Extension entomologist, cautions farmers about using soil insecticides in fields planted to GM hybrids.

"Our general attitude is that we do not feel like it is worthwhile, necessary or cost-effective unless you are under extremely severe pressure," he says.

University of Illinois Extension entomologist Mike Gray says increased use of soil insecticides boosts risks to non-target organisms and might elevate human health and safety concerns.

Brown applies a granular soil insecticide on two-thirds of his ground, which is planted to continuous non-GMO corn. He uses the AmVac SmartBox closed-application system, which reduces his exposure to active ingredients. A 24-row SmartBox System retails for about $15,300.

Brown will plant one-third of his corn acreage this spring to a multiple-trait hybrid and forego soil insecticide. But, he’s concerned how well such hybrids will hold up long-term to rootworm pressure. "We’re going to have to adopt more than one method of control to get ahead of these bugs."

How to Evaluate Corn Rootworm Pressure

If you’re unsure whether your fields warrant a soil insecticide for corn rootworm control, try one of these two methods recommended by Burrus Seed Company.

Root Dig Method

1 Walk fields in July and August; record rootworm beetle populations.

2 Dig roots then to evaluate control in traited and refuge acres.

3 If the rootworm beetle population is high and root ratings of rootworm-traited hybrids are .25 or higher in the field, use a granular soil insecticide next year.

Rootworm Beetle Count Method

Scout rootworm-traited acres at pollination.

2 Examine four consecutive plants in five areas of the field. Start at the base and count rootworm beetles on leaf surfaces, leaf axils, stalk, ear tip and tassel. Determine the average number of beetles per plant.

3 If the average beetle population is .75 beetles per plant or more, consider using a soil insecticide with rootworm-traited corn in 2014.

4 If the rootworm population is less than .75 beetles per plant, wait two weeks and scout again.
When the beetle population stays low for six weeks after the first scouting, no soil insecticide is necessary with rootworm traits.

For more information on the corn rootworm pest and how to assess fields for infestations, visit

You can e-mail Rhonda Brooks at

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