Slugs! Protect spring plants from hungry mollusks
by Mary Robson, Area Horticulture Agent, Washington State University
Some slugs are natives here, such as the banana slug, a handsome creature that may grow to 8 inches long and appears in colors from lemon yellow to dark brown, with black blotches. The native slugs dispose of fallen forest litter and contribute to the health of forests; in local Skagit tribe legends, they symbolize patience and persistence. The native slugs generally do not bother urban and suburban gardens.
We have hungry immigrants--the European black slug, familiar to gardeners as the black, or reddish brown and voracious eater which pulls itself into a hump like a speed bump when not rasping leaves. Others, the great gray garden slug, and the greenhouse slug, can do astonishing amounts of damage, rasping and digesting over 40 times their weight in one night. (This is not a pretty sight!)
Look at slugs this way: When we plant gardens in their territory, we supply slugs with ample forage. To manage slugs, it's necessary to know their habits. Slugs emerge to forage primarily at night, or in cool, moist mornings when foliage is wet. During long cloudy spells, they may come out at any time. (This may mean most of the month of June!) Hot, exposed locations don't attract them, and some plants, such as herbs that are grown in sunny, baked areas, will not be bothered by slugs. Remove loose boards, piles of garden trash, and litter where they like to hide. Ground covers, which have many garden uses, can unfortunately also offer shelter to slugs. If your garden is located near a "wild" or forested area, the problem will be worse.
Container plants offer good spots for hiding slugs. The mystery of why summer annuals develop holes in leaves may be solved by tipping the pot and checking for small slugs living around the drain hole in the bottom of the pot.
The quickest method of getting rid of slugs is hand-picking them off plants or the ground (scoop or pluck with gloves on) and dropping them into a can of water with a little rubbing alcohol added. One humane gardener puts them into the freezer, which dispatches them quickly. (This requires explanations to other household members first!) Patrol in the early morning or two hours after dark with a flashlight. Persistence with this method can really work.
Get rid of any eggs you find; slugs lay from 12 to 100 eggs at a time. All slugs are hermaphroditic, which means they each possess both male and female organs and don't have to hunt for a mate of the opposite sex. This saves time! Slugs can lay eggs when they are three months old, and can live from one to six years. Slug eggs resemble small pearls, and are found tucked in clusters against logs, under rocks and in the soil. Stomp on the egg clusters. More eggs are laid in late summer and early autumn than in spring, but check now to destroy over-wintering batches.
Here are some other tips for controlling slugs:
- Trap them under boards or overturned flowerpots. Put one dampened pot inside a larger one, and set them in a shady place. Prop up the edge of the larger pot and check inside on sunny days to find slugs which have crawled in.
- Beer traps do collect slugs; put the container into the ground with an inch of lip protruding to keep ground beetles and other beneficial insects from stumbling in. Slugs don't like their beer rain-diluted or dirty; refresh traps often.
- Hand-pick faithfully; vigilance does help.
- Remove plants that are most susceptible to slug damage. Lettuce gardens, for instance, are no fun at all when salads have baby slugs in them.
- Many Northwest gardeners are finding that copper barriers (builders flashing or copper strips sold as slug traps) do help.
- Commercial poison baits, if they are chosen, must be used with caution. Put all baits inside covered containers, such as yogurt cartons. Uncovered piles of bait may be dangerous to children and are definitely poisonous to cats, dogs, and birds. In addition, rain and mold reduce the effectiveness of baits, so cover it for safety and utility.