CONSERVATION TILLAGE CROP YIELDS IN RELATION TO GRAY GARDEN SLUG [DEROCERAS-RETICULATUM (MULLER)] (MOLLUSCA, AGRIOLIMACIDAE) DENSITY DURING ESTABLISHMENT

Alfalfa, soybeans, maize, turnips and wheat crops established by conservation tillage, and that had been subjected to no slugs, medium or high densities of slugs Deroceras reticulatum (Muller) at sowing, were harvested. The crop yields were inversely related to slug density, and seedling damage and mortality during crop establishment. Alfalfa and wheat suffered high levels of seedling mortality and their yields were reduced by up to 80%. Soybean yields were reduced by 25-46% at the medium and high slug densities, which parallel plant survival after slug attack during establishment. Maize grain yield was reduced by similar to 32% at medium and high slug densities in 1989, but drought conditions in 1988 precluded a grain harvest and there was no reduction in total plant yields where slugs were present at establishment. Turnips, which suffered only minor losses from slugs during establishment, consequently showed no yield reductions at maturity.