Moist, high residue environments are a slug’s delight. Slugs are sporadic pests of corn primarily associated with no-till practices and heavy crop residue. Their outbreaks are increased by cool, moist springs, mild winters and manure. While not widespread most years, slug injury to corn and soybeans was severe in some states in 2010 and localized outbreaks were reported in some areas in 2015, 2016, and 2017. Corn and soybean fields planted into heavy crop residue are most likely to see damage from slugs. If eggs hatch at crop emergence, slugs can cut off corn coleoptiles and soybean hypocotyls, resulting in severe stand losses.
Figure 1. Adult gray garden slug
The adult gray garden slug is one to two inches long when fully extended. It varies from gray to pale cream and has a light mottled pattern of spots and streaks. The young are the same shape and coloration as the adults. The “slime” they give off is a protectant against environmental stressors. Slugs are nocturnal, meaning they emerge and feed above ground after dark.
Figure 2. Three small slugs present on and near a corn plant.
Figure 3. Leaf damage caused by juvenile slugs
The life cycle of the slug starts with eggs. Females lay eggs in masses in the soil in the fall, which are held together by a sticky secretion that turns yellow before hatching. Eggs hatch in about one month, producing small slugs that closely resemble adults except in size. Slugs primarily overwinter as eggs; however, adults can also overwinter. Overlapping generations occur because of the slug's ability for summer - long breeding during favorable conditions. They can live about 12 to 15 months. There is one generation per year.
Figure 4. No-tilled field in Barron County, Wisconsin. (Photo courtesy of Jim Boersma.
Figure 5. Slug damage to root systems of a hybrid with Bt corn rootworm protection, which does not protect against slug damage. (Photo courtesy of Dave Johnson.
Slugs are capable of feeding on leaf tissue throughout the growing season, slowing early growth. This leaf feeding is often only cosmetic and if the crop can send out new leaves, it can often “outgrow” slug infestations. No-tilled fields are impacted the most severely (Figure 4). Slugs are mollusks and not susceptible to Bt proteins that control many above and below ground insects. Heavy slug feeding on brace roots can result in root lodging under windy conditions (Figure 5)
In fields with a history of slug damage, preventative practices to reduce risk of damage include:
Figure 6. Adult slug feeding on a corn root; Pierce County, Wisconsin, 2010. (Photo courtesy of Jim Boersma.)
The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. Product performance is variable and depends on many factors such as moisture and heat stress, soil type, management practices and environmental stress as well as disease and pest pressures. Individual results may vary. FF171206 (200709) December 201