Close-up of a wireworm in the soil at the root of a corn plant. John Obermeyer, Purdue University Extension Entomology
WIREWORMS ALIVE AND WELL: You won’t find wireworms or other secondary pests in every field every year, but if you find them once in any year, they can devastate that field, agronomists note.

Seed-coated insecticides target more than corn rootworms

Corn Best Beat: Advisers point out reasons for staying with a high rate on seed treatment.

Rootworm activity was reportedly low in many areas this year. A recent report from Purdue University implied that seed-coated insecticides move off-target in planter dust from using talc and could damage honeybees. So do you really still need the high rate of seed-coated insecticide on corn? In most cases, that’s the 1250 rate of whichever product was used to coat your seed.

Agronomists on the other side of these arguments are quick to point out that just because rootworms didn’t cause much damage in an area this year doesn’t mean they’ve gone packing. Plus, rootworm is often not the main target for these higher rates, anyway. Instead, it’s secondary pests. And despite what some Purdue reports say, several agronomists believe secondary pests can still hit yields hard when and where they show up. Many also believe common sense and reason need to be infused into the honeybee discussion.

Here is the exact question someone wanted the Indiana certified crop advisers panel to answer. “Reports I’ve heard this year from entomologists indicate that corn rootworm was a nonfactor in most areas. Is there any reason to be buying and planting corn treated with the high, 1250 rate of seed-applied insecticide? Isn’t the high rate mainly to control corn rootworms?”

Advisers’ comments
This month’s CCA panel includes Betsy Bower, agronomist, Ceres Solutions, Terre Haute; Jamie Bultemeier, agronomist and corporate sales director for A&L Great Lakes Labs, Fort Wayne; and Steve Gauck, sales agronomist for Beck’s, based near Greensburg.

Bower: Reasons to be buying the high rate would include problems with secondary pests such as wireworms, seed corn maggots and white grubs. We do have certain fields or soil types that can have yearly infestations of all three pests. The low rate of Poncho — Poncho 250, for example — will only provide fair control of flea beetles and seed corn maggots, but good control of wireworms and white grubs. The high rate provides excellent control of all of them.

Bultemeier: While corn rootworm is the main target of the 1250 rate, field reports indicate longer and more complete control of other soil pests like wireworm, cutworm and grubs. Rootworm populations may be declining, but the 1250 high rate provides an additional layer of control for minor rootworm populations.

Gauck: The high-rate of seed treatment insecticide is designed to help in areas with moderate to light rootworm pressure. Rootworms largely have been a nonfactor in my area this year. That doesn’t mean they won’t be a factor in the future. 

The high rate of seed-coated insecticide also gives you more control over other pests such as wireworms, seed corn maggots and black cutworms. It’s an insurance policy, but if you have had high pressures of insects in the past, it may still be worth it.

There is another factor to consider here. Also think about planting time and condition of the soil. If you’re planting early into cool, wet soils or into no-till, there can be an advantage of having the extra insect protection of one of these products at the 1250 rate.

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