Issue No. 10, Article 5/May 28, 2004
Slugs in No-Till, Part II
Due to a mysterious electronic glitch, the article "Slugs in No-Till" (issue no. 8, May 14, 2004) did not appear in its entirety. The full article follows as well as some new information on slugs that has been reported since then.
Slugs are not really something that comes to mind when I think of spring insect problems. Maybe that's because they're not insects but mollusks. Or maybe it's because we truly don't find slug problems on a regular basis.
Slug on seedling soybean (Photo courtesy of Bill Lindenmeier).
Slugs are sporadic pests of corn, and their activity is generally greatest in late spring and early summer. As conditions become hot and dry, slugs enter an inactive state and then become active again in the fall before hibernating in the winter. Overall, slugs will likely cause little injury in most fields. In fact, they are generally associated with conservation tillage practices such as no-till. Undisturbed soil lets population densities of slugs increase. Slugs overwinter as both adults and eggs. Egg hatch occurs in late May to early June; feeding by juveniles soon follows.
Slugs and injury to soybean seedling (Photo courtesy of Ed Corrigan).
Slug injury to soybean seedling (Photo courtesy of Bill Lindenmeier).
Injury is most often seen when cool and wet conditions exist. Planting into wet soils may also increase the potential for slug injury. Seed furrows may not completely close when planting in wet conditions, leaving the furrow open for slugs to feed on germinating seeds. This injury is similar to injury caused by wireworms. When slugs destroy seeds, severe stand loss may occur. Slugs feed mainly at night, hiding in cool, moist places (under debris) during the day. The telltale sign of slug feeding is the presence of slime trails from their movement across the foliage. Slugs rasp the surface of the seed or plant foliage when they feed. This causes the streaks or holes on both the seed and leaves. Stunted, lower-yielding plants may result from slug feeding, and heavy defoliation may result in plant death and stand losses.
A few reports of slug injury in no-till soybeans have occurred over the past 10 days. Bill Lindenmeier, crop systems educator in Ogle County, found slugs feeding in a first-year no-till soybean field following CRP. In areas of heavy residue, slugs were feeding on cotyledons and missing soybean plants. Bill also noted that while most of the soybeans will grow out of the injury, areas with severe damage will require replanting. Slugs were also found feeding on no-till soybeans in Kane County. Slugs have been found in southern Illinois as well. Mike Plumer, natural resources management educator, has looked in several fields in Saline and Hamilton counties. Slugs were found in all the fields, although the number of slugs in each were few, and he observed very little slug damage to corn.
Research by Ron Hammond of Ohio State University has shown that primarily four species of slugs are numerous enough to be considered of potential economic importance. The gray garden slug is the predominant species found in fields, followed by, in order of abundance, the marsh slug, the dusky slug, and the banded slug.
Slug injury to emerging soybean seedling (Photo courtesy of Ed Corrigan).
Slug injury to corn seedling.
Both corn and soybean can tolerate some slug injury; however, there are very few economically viable rescue treatment options. Limited spot treatments with a molluscicide (metaldehyde) may be an option in severely infested areas. Switching to a reduced or conventional tillage program the following year will help decrease slug populations.--Kelly Cook