Slugs
Identification and Incidence: Slugs are not insects, they are molluscs and more closely related to snails and clams than to insects. In field crops, slugs are particularly prevalent in no-till or reduced-till fields with heavy residue and little soil disturbance. They can eat virtually all crops and inflict most of their damage during crop establishment and early growth in the spring and fall. This damage tends to be most severe under cool, wet conditions, which slow crop growth and favor slug activity. Slugs typically feed at night and hide in residue or soil during the day. They range in color from pale cream to gray to shiny black and range in size as adults from less than an inch to over 2 inches in length. Small juvenile slugs can damage seeds and seedlings reducing stand and may defoliate established stands that may delay plant development. Slugs damage soybean by destroying the germinating seed prior to emergence and causes significant defoliation.
Sampling: Inspect several areas of the field and determine percentage of plants being fed upon and percentage defoliation. Another approach to finding slugs is to place artificial shelters across a field (1 X 1 foot shingles, old boards, or anything to create a dark, cool, moist environment). Several days after putting them out, slugs can be found under the shelters during the day. Research suggests that if you consistently find one to two slugs per shingle in the early season that you may end up with damage. In autumn, scouting for eggs can also reveal details on populations to expect in spring. Research has not been able to identify consistent relationship between the amount of slug damage to soybean plants and yield loss.
Economic Threshold: Treatment may be necessary if defoliation is greater than 40 percent on slow growing plants or if plants are being killed.
Management Options: Several bait formulations of metaldehyde or chelated iron are labeled for slug control. Research indicates that ground beetles and other predators can be significant allies in the fight against slugs; populations of these predators will be strongest in fields that avoid preventative insecticide applications.