Slugs and snails are one of the most universal garden problems.  These mollusks are not insects, so insecticides are not effective.  Slug and snail control starts in late summer or fall, and each over-wintering pest lays up to 400 eggs which will hatch in the spring.  Clean up debris and weeds where they hide in the fall and apply bait during the growing season.
Iron phosphate is an effective snail/slug control and has little off-target toxicity.