Jarrod Miller, Extension Educator, University of Maryland
As planters hit the fields it is a good time to review the conditions that may cause slug damage to your fields. Some factors that increase the incidence of slug damage include 1) fields with heavy residue (no till, cover crops, manure, ect), 2) mild winters that allow eggs to survive, 3) temperatures between 63 to 68F plus 75% soil moisture, and 4) growing conditions that slow crop development in the spring. Across Maryland, moisture contents will vary, but recent rainfall and cooler temperatures on the lower shore has produced soils close to field capacity.
A survey performed by Virginia Tech in 2013 gathered data to determine what cropping systems may produce the most slug damage. This survey revealed that no-till soybeans following corn with a cover crop observed the greatest damage. Overall slug damage appeared to be higher in no-till fields following corn for grain the previous year and in those fields with a cover crop. Planting no-till corn or soybean following grass hay did not appear to result in slug damage.
Slug eggs typically hatch from the beginning of May through early June. Juvenile slugs cause the most damage, as they feed on recently emerged corn and soybean plants in late May and early June. Corn planted prior to eggs hatching helps get a head start and prevent severe damage. Since soybeans are typically planted as juveniles emerge, it is a little harder to control. Based on the information from Virginia Tech, it would be best to focus scouting on no-till soybean fields that followed corn grain and a cover crop. All no-till fields are likely to have some slug presence though. Wet fields where seed slots do not close properly also allow slugs to feed directly on the growing point.
For control, the Virginia Cooperative Extension Pest Management Guide recommends metaldehyde at a broadcast application of 10-12 lbs/acre. Results of a study in 2010 indicate the bait could be effective, but that 0.5 inches of rain may cause the bait dissolution. In most cases slug feeding reappeared three weeks after bait application, and could have been due to rain. Management by timing planting may be the most cost effective option, or tillage where heavy infestations require more drastic measures.
Virginia Tech also has a scouting protocol online with photos to rate the level of injury. They recommend scouting to being when plants emerge and continue to the V5 stage (corn and soybeans). For more information on scouting and slug damage, see the Virginia Cooperative Extension webpage for Shenandoah County.
Clark, R., W. Thomason, B.Jones and A. Vallotton. 2010. How Well Does Slug Bait Work?. Virginia Cooperative Extension.
Clark, R. R. Youngman, and A. Vallotton. 2008. Slug Management in Continuous No-Till. Virginia Cooperative Extension.
Purdue Extension. 2009. Slugs. Field Crops IPM Website, Purdue University.
Clark, R. 2013. Observations of Management Practices and Their Effect on Corn and Soybean Damage Due to Slug Feeding. Virginia Cooperative Extension.
