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Serving: IN
wireworm on soybean seedling John Obermeyer, Purdue Extension Entomology
SOIL PEST: If wireworms are present, cool wet soils will likely bring them out. This picture illustrates how wireworms can kill soybean seedlings.

Cool, wet stretch sets stage for seedling insect issues

Soybean Watch: Wireworms and slugs can cause problems in years like this one.

Two years ago in parts of the eastern Corn Belt, especially in central and southern areas, was the year of the slug. Cool, wet conditions helped slugs stay around much longer than normal. Steve Gauck was finding slugs at the end of June in 2017, and even found live slugs in relatively late-planted soybeans at the end of July. That’s unheard of in most seasons.

Does that mean you will have slugs affecting soybean germination and emergence in 2019? Not necessarily, but you should be aware that they’re more of a threat in cool, wet years when moist conditions persist into the early growing season, Gauck says. Gauck, Greensburg, Ind., is a sales agronomist for Beck’s who is scouting this year’s Soybean Watch field. Soybean Watch ’19, focusing on a field in central Indiana, is sponsored by Beck’s.

The biggest problem with slugs is that you can’t take remedial action if you find them. There is precious little you can do to prevent them, even if you suspect conditions may be right for them to be active and become a threat to soybeans, Gauck says.

“What you can do is scout and know how they are affecting stands,” he adds. “If you have 80,000 plants left, and they are fairly well distributed, you would probably opt to leave the stand. If you get much lower than that due to slug feeding, you may opt to replant, depending upon where the calendar is when you make the determination.”

Other pests

Dedicated scouts once put out bait stations for wireworms in fields where they suspected damage, Gauck says. While that’s not done often today, it’s still an effective tool if you suspect they might be a problem.

Wireworms tend to show up in areas where there were large amounts of organic matter, either on the surface or incorporated into the field at some point in time. Once wireworms show up in an area, their life cycle allows them to remain in that spot for the next several seasons. It’s often a low spot within a field where organic matter is higher, although wireworms aren’t limited to low, heavier soils.

Bait stations consist of a handful of grain, such as corn or wheat, placed in a shallow hole dug in the ground. The scout places black plastic over the hole after covering over the grain, and then flags it. Germinating grain under the plastic gives off odors that attract wireworms if they are present in the area. Scouts check wireworm traps a few weeks after placing them to see how many, if any, wireworms have migrated to the pile of germinating grain.

While it’s too late to put out bait traps now, it’s an idea to consider for the future if you or a scout determines that wireworms affected one of your fields this spring. This pest also attacks corn seedlings.

The best remedy for wireworm issues once they are at work in the field is hot, drier weather. Once soil temperatures become warm, wireworms tend to quit feeding and move deeper.

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