If you can kill the slugs before they lay eggs, you have won half the battle. For growers who do not irrigate in the summer, bait is most effective when broadcast in late September or early October, when slugs come to the soil surface to feed, mate and begin laying eggs. However, in regularly watered gardens and row crops, slug bait is helpful anytime, as the slugs don't hide underground as much as in unirrigated sites. Winter and spring rains can make an otherwise effective bait perform miserably. Bait shyness has also been seen.
Slugs avoid feeding on baits if they consumed a sublethal dose the first time.
Apple pomace-based baits are not very effective on slugs in Oregon. And carbaryl in a bait greatly reduces populations of earthworms and predator beetles, beneficial creatures in farming and gardening. Only this spring did they begin to reappear. Most of these slugs came from unhatched eggs that can withstand long periods under water or populations of mobile slugs that made it to a high point in the field. It's not always glamorous being a slug researcher, but according to Fisher, DeFrancesco and Horton, those early mornings slogging through the mud, counting dead slugs and digging plugs of grass and soil to take back to the lab do have their charms.