Steve Gauck mused that it would be strange to still find slugs in the Soybean Watch ’17 field when he prepared to scout in very late July. Slugs normally disappear around June 1. Typically, warmer temperatures drive them deeper into the soil.

If 2017 is anything, it’s not a normal year, says Gauck, sales agronomist for Beck’s, based in Greensburg, Ind. Beck’s sponsors Soybean Watch ’17. He found slugs after being in the field on a hot July morning for less than 10 minutes.

“This slug shouldn’t be here, but it is,” Gauck commented at the time. “It’s not going to do damage because these soybeans have outgrown it.  But the thing worth noting is that it’s still here.”

Why slugs?
Slugs don’t cause much noise among soybean growers most years. In 2017, however, cool, wet soils persisting into June set up ideal conditions for slugs to proliferate and stay active longer than normal.

“Replanting due to damage to emerging seedlings was common,” Gauck says. “Slugs thinned stands in some fields to well below 80,000 plants per acre and made replanting necessary.”

The Soybean Watch ’17 field was planted in early June. Gauck found slugs when first scouting the field at the end of June. In some of the lowest, wettest parts of the field, he estimated that slugs contributed to reduced stands as low as 80,000 plants per acre. “That should still be enough plants to reach maximum yield potential,” he says.

Stunted or missing plants were generally more common if the soybean row fell upon the old corn row. Gauck speculates that those areas were likely cooler and wetter, and most attractive to slugs.

The problem with slugs is that there’s no remedy once you find them, and there’s nothing you can apply to prevent them from coming back if you replant.

“As long as the top few inches of soil stayed moist, it probably stayed cooler than normal, even though air temperatures heated up,” Gauck says. “That may have enabled slugs to persist far longer than normal.”

Cover crop concerns
Some people are nervous about seeding cover crops again. While some fields with cover crops had slug problems, some didn’t, Gauck says. And some fields that didn’t have cover crops had slugs.

“It’s not as simple as just blaming cover crops,” Gauck says. “This was the worst year for slugs in quite some time. There’s no way to know if they will be an issue next spring. It will depend primarily on weather conditions.”

One thing that might help is making adjustments so you close the seed trench completely. “Open seed trenches may make it easier for slugs to move down rows,” Gauck says.

Here’s the bottom line. “I wouldn’t back off cover crops just because of fears about slugs,” he concludes.