Slugs were a problem in a few corn and soybean fields last season as they are most years in no-till. Very little corn or soybeans have been planted in Butler County by May 1 because of wet field conditions. We need to watch for slug damage, especially this year since the crop may be emerging in the midst of newly hatched slugs.

Crop injury due to slugs may include early injury to seeds and seedlings, reducing stand establishment, and defoliation of established stands that may delay plant development. The mouth of a slug includes a tooth-covered tongue called a radula, which is used like a rasp to grate its food. As a result, a slug feeds on the surface of a seed or foliage by rasping the surface. The damage may appear as streaks or holes. When slugs feed on germinating seeds, they will hollow out distinct holes appearing like damage due to wireworms.

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. When such damage occurs in the seed furrows, and the soil surface is damp, the slugs often can be readily found near the site of damage.

Most field slugs pass through a single generation per year and overwinter in the egg stage. However, if the winter is mild, adults may survive. Since field slugs may live 12-15 months, and eggs are laid in the early spring and fall, overlapping generations of adult and juvenile stages may be found. Peak slug activity occurs in late spring and early summer when the spring hatch attains adult growth.

No-tillage corn and soybean fields should be scouted routinely to detect the presence of slug problems, especially when cool and wet conditions prevail during the months of May and June. If enough stand loss occurs to warrant replanting, a rescue treatment of slug bait may be justified prior to replanting.

In general, both corn in the early whorl stage and soybeans in the vegetative stage can tolerate up to 30 to 40 percent defoliation without a significant impact on yield. If growing conditions are unfavorable and stand loss is anticipated, then corrective action may be needed. In general, if the corn or soybean crop has advanced to a point where only the lower foliage is being affected, the crop will overcome the impact of slug defoliation.

When corrective action is required to reduce slug population, commercial formulated baits can be applied. Such commercial formulations can be expensive to apply, but the cost of such treatments can be maintained at about $10 to $15 per acre if applied selectively.

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.

This farm news was published in the May 10, 2006 issue of Farm World.