Slugs are mollusks that like moist, cool conditions in the spring and residue to hide under. That makes no-till or minimum tillage fields a target. In most years there might be a few scattered reports of slug damage. This year there have been lots of reports from south-central and southeastern Indiana, and well into Kentucky, particularly in soybeans that were planted in mid-to-late May after soils dried enough in those areas to allow planting. Much of Indiana has been dry, but this area has been on the wet side until recently.
Terry Vissing called me to Clark County to look at slug damage in soybeans. We found plenty of damage, although usually in spots within a field, not in the whole field. We also found the slugs still present on the surface under residue.
In corn planted into cover crop wheat residue, there were signs of slug feeding on a few bottom leaves. But planted early, the corn apparently outgrew the slug problem. There did not appear to be missing plants, only a plant here and there where bottom leaves showed signs of slug feeding.
Slugs are often more of a [problem in corn than in soybeans. In fact, in the Purdue University Corn & Soybean Field Guide published by the Purdue Crop Diagnostic Training Center, slugs are listed with insects in the corn section, not the soybean section. However, slugs are not insects. They are actually mollusks. That makes them harder to control, either in advance if you suspect problems, or once they show up.
Slugs working on corn leaves produce ragged holes. The leaves may appear shredded. The problem can be so bad in younger corn that the field takes on a grayish cast from the feeding, and replant may be a possibility. However, in larger corn, like that of Vissing,’ the damage is negligible, if a factor at all. Lower leaves don’t contribute much if any to final yield.