WEST LAFAYETTE, Ind. — A wet spring that has delayed
fieldwork in Indiana has created conditions ideal for slugs to thrive, a Purdue
Extension entomologist said.
Slugs are most common in no-till systems and weedy fields.
These mollusks without shells can wreak havoc on corn and soybean seedlings —
especially when seed slots aren’t properly closed at planting.
One way for farmers to know whether they should expect slug
activity this spring is to consider field history.
“Slugs don’t fly in,” John Obermeyer said. “If you had slugs
last year, you’ll have slugs this year.”
The problem with these pests is that they are nearly
impossible to control. Regular insecticides, whether granular, liquid or
seed-applied, are ineffective because slugs slime over them.
While some baits can be used in corn, Obermeyer said the
expense and difficulty of distribution make them impractical as anything other
than a last resort.
Instead, growers should focus on environment disruption by
managing weeds and crop residue, especially in avoiding the matting of dead
plant material on the ground.
“Tillage is the best option in many cases where we have
established slug activity,” Obermeyer said. “Row cleaners give the seedlings an
advantage to get up and going, which is the best medicine in many cases for slug
Once crops are planted and have emerged, growers can
identify slug-feeding damage in corn by the linear scars on leaves. In severe
cases, corn leaves might be tattered in a way that resembles hail damage.
In soybeans, slugs feed on the hypocotyl and cotyledons,
rather than the foliage.
If feeding is minor, both corn and soybean plants will often
outgrow the damage. In severe cases where the plant’s growing point is damaged,
recovery is unlikely. Such damage widespread in a field could warrant