There’s really no way to sugarcoat it: Slugs are gross. I grew up in the Pacific Northwest, where the slugs are black and brown sacks of guts up to six inches long. They’re easy to spot and collect. Our weapon of choice against them was table salt, which we sprinkled liberally over their pudgy bodies. I should have charged my parents a nickel per slug to fund my comic book habit.
The slugs we find in San Diego look like gray blobs of mucus, and leave a slime trail much like that of a toddler with a runny nose. They are, however, one of the easier pests to control if you are patient and consistent.
Slugs and their cousin snails are mollusks. They feed by scraping holes in plant leaves with a toothlike body part called a radula. They like it damp, so you would think they would not be a problem here in arid San Diego. However, irrigation creates ideal conditions for them, as does the May gray/June gloom weather pattern we have been seeing for too long this year.
Two methods from the integrated pest management (IPM) playbook are particularly effective at combatting slugs and snails. Cultural controls limit the places and conditions that attract these pests. Avoid overwatering and overplanting. Slugs like damp places and shade. Make sure plant debris is cleaned up, as it often holds moisture. Overplanting makes it easy for slugs to hide and harder for you to find them when you practice mechanical control.
Mechanical controls include handpicking and traps. Handpicking may not be appealing if you are squeamish. Best to pay your child, or a neighbor’s child, a bounty per slug. Handpicking is most effective in the morning before the slugs have gone to their siesta spots out of the sun. Daily picking is a good idea if there are lots of slugs. The schedule can drop to a couple of times a week once the population drops off or moves to someone else’s garden plot.
Traps are also very effective. Beer traps can be fabricated from plastic cups or any container with steep sides. Some traps have lids on top with holes for the slugs to fall through. Open topped traps work too; just make sure the slugs can’t climb back out. Traps do need to be maintained and the dead slugs removed. Watering dilutes the beer in open traps or the beer evaporates—and then there’s the question of whether to serve them Heineken or a nice craft IPA. A sugar-water and yeast mixture will also attract them and keep you from having to check their IDs at the trap door.
A simple trap can also be made by propping a board up somewhere inside your raised bed. The slugs will be attracted to the shade and damp underneath it. An upside-down melon rind is also attractive to them. The surface of the trap should hold some moisture. I tried a concrete tile. It attracted shade-seeking pill bugs, but no slugs. I leave it you to decide how to dispatch the slugs once they have congregated. Salt is no longer recommended, but smashing, squishing, and scraping them from the board surface all come to mind. Happy hunting!
More information on fighting slugs and snails can be found in these web pages: Slugs and Snails and California's Pest Snails and Slugs.