In the C.O.R.N. newsletter three weeks ago, Ron Hammond, OSU Extension entomologist suggested it was time to start watching fields for slugs.

Weather conditions have been perfect for slugs, cool and wet. I was in a field of corn on May 21 where, in areas of the field, 100 percent of the corn plants had been fed upon. Some were chewed so badly the first two leaves were gone. We found newly hatched juvenile slugs feeding on every plant.

This was a no-till cornfield, corn after corn, so there was an abundance of residue to keep the soil damp and cool. The farmer had sprayed for winter annuals last fall, so there were no weed problems, which I’m sure would have made the problem even worse.

The amount of damage from the slugs varied through the field. As you would expect there were “hot spots.”

Field damage to germinating seeds and early developing seedlings can be devastating. In no-tillage fields, slugs will actively feed on germinating seeds and plant embryos, especially if the seed furrow is covered by a moist surface residue. In years having favorable
conditions for slug development, stand loss ranging from 50 to 90 percent have been observed.

Since foliar injury is generally observed during the day when slugs are not active, the tell-tale sign that the damage was caused by slugs is the trail of dry mucus that remains from earlier movement by slugs across the foliage.

When corrective action is required to reduce slug population, commercial formulated baits can be applied. Currently, there are two types of slug control available. There are three brand names which are methaldehyde-based and one that contains iron phosphate.

Such commercial formulations can be expensive to apply, but the cost of such treatments can be maintained at about $15 per acre if applied selectively, only treat hot spots.

When applying baits for slug control, it is very important that the bait be applied when the slugs are at peak activity above the soil surface. Bait application should only be applied during periods of ideal temperatures and wet conditions favorable to above ground slug activity.

Other options for reduction of slug problems do exist. Occasional use of reduced tillage decreases the development of slug problems in fields that were maintained under long-term no-tillage practices. Mechanical devices on planters that remove residue over the seed furrow may reduce slug damage to seeds and emerging seedling. If replanting is required, tillage is recommended, opening up the soil helps drying and exposes the slugs to birds.

Reduction of slug populations, once they have become established, is difficult to achieve since the bait treatment only reduces the slug activity buying time to enable the crop to outgrow the problem. Many growers have learned over time how to minimize or tolerate the impact of slugs in no-till corn and soybean production.
Remember that corn planted on April 30 with a population of 15,000 plants at harvest has a potential equal to or greater than corn planted on May 29 with a population at harvest of 30,000 plants.

The views and opinions expressed in this column are those of the author and not necessarily those of Farm World. Readers with questions or comments for Steve Bartels may write to him in care of this publication.