ECONOMIC INJURY LEVELS TO FIELD CORN FROM SLUG (STYLOMMATOPHORA, AGROLIMACIDAE) FEEDING

Slugs are important corn pests, but little is known about how their fe eding on corn seedlings affects grain yields. Individual corn plants w ere infested with juvenile slugs, Deroceras reticulatum (Mueller), at four densities at the following three stages of growth: before seedlin g emergence and at the two- and four-leaf stage. Feeding injury to cor n seedlings by slugs was scored visually for leaf area loss. Yield of roots, stalks, and grain (Y) was regressed against maximum injury esti mates (X). Considerable plant mortality resulted from the highest slug density (5010.1 m(2)) in 1989. Therefore, lower initial densities (up to 20/0.1 m(2)) were used in the following 2 yr to study the effects of sublethal injury. Less plant mortality resulted from the lower init ial slug densities used in 1990 and 1998. A significant linear relatio nship between yield of grain and maximum leaf injury occurred in 1989. A quadratic regression equation best described significant losses in grain yield from slug feeding in the combined years of 1990 and 1991. The linear and quadratic equations were used to establish economic inj ury levels (EILs) relative to the cost of slug control and the value o f the corn crop. EILs ranged from 2 to 20% defoliation by slugs in 198 9, which was a warm, wet season. EILs ranged from 39 to 59% defoliatio n by slugs in the combined years 1990-1991, which was characterized as cool and dry in 1990 and warm and dry in 1991.