Slugs and snails: traps, barriers and baits

Slug, snail or something else?

Both are mollusks; slugs lack the snail's external spiral shell (UC IPM). Minnesota describes slugs as soft-bodied, legless and usually brown or gray, from about 1/4 inch to 2 inches or longer; Penn State gives 1/4 to 10 inches, though most are under an inch. Earwigs, caterpillars and other chewing insects leave similar holes, so look for the silvery slime trails that confirm recent slug or snail activity (UC IPM). Oregon State adds ragged holes with smooth edges between leaf veins and sausage-shaped droppings (OSU EM 9155).

UC IPM names the brown garden snail (Cornu aspersum) as the most common problem snail in California gardens, and the gray garden slug (Deroceras reticulatum) among several slugs. Oregon State counts about a dozen important slug species in Oregon gardens (OSU EM 9155).

When they feed

• Time of day. Most active at night and on cloudy or foggy days; they hide from heat and bright light (UC IPM). Oregon State says they feed at night when it is above 50°F, winds are light and humidity is high (OSU EM 9155); Penn State says they become active, hatch, feed and lay eggs above 40°F.
• Season. Most active in spring and fall, less in summer heat and winter cold (OSU Extension article). In mild areas such as southern coastal locations they may be active year-round (UC IPM).
• Eggs. In Oregon, slugs lay eggs in fall, usually late September or early October when the rains start (OSU EM 9155); the eggs overwinter and hatch quickly in spring (OSU Extension article). Minnesota says slugs overwinter as eggs in protected soil or under debris, mulch or boards, hatching in spring and early summer.
• Out of sight. The Oregon Master Gardeners write: "Only 5% of slugs are above ground at any one time."

Crops at risk

UC IPM lists basil, beans, cabbage, lettuce, strawberries and many other vegetables as often damaged, along with seedlings and low-growing ripening fruit such as strawberries and tomatoes. Lavender, rosemary, sage and nasturtium are less attractive. Heavy feeding can injure or kill seedlings and reduce harvests, while plants in full sun are rarely affected (UMN). Spring damage lasts: "once the leaves are nipped, the damage is there all summer," says OSU Master Gardener Claudia Groth.

Step 1: take away shelter and moisture

1. Remove boards, stones, debris, weedy areas and dense ground covers such as ivy (UC IPM), and loose bricks, trash piles and weeds (Penn State). Where shelters cannot be removed, such as deck undersides or water meter boxes, trap there regularly (UC IPM).
2. Place vegetable beds as far from hiding places as possible (UC IPM).
3. Raise pots on bricks or feet and pull mulch back from vulnerable plants (OSU Extension article). Minnesota also advises limiting mulch and removing excess leaves in spring.
4. Water in the morning, not the evening (OSU EM 9155, UMN). UC IPM suggests switching from sprinklers to drip and irrigating near sunrise; Minnesota waters the root zone with drip or soaker hoses. See drip irrigation for containers.
5. Thin plants, prune low branches and keep rows narrow, about 12 to 18 inches wide (UMN).
6. Disturb eggs: work the soil 4 to 6 inches deep (OSU EM 9155). If eggs are found, shallow cultivation brings them to the surface to dry, and solarizing raised-bed soil kills them (UC IPM).

Step 2: hand-pick and trap

Search with a flashlight about 2 hours after sunset or in early morning (OSU EM 9155). UC IPM waters the area in late afternoon to draw them out, checks daily at first and weekly once numbers drop, and advises gloves. Drop them into soapy water (UMN, OSU Extension article). Do not use salt: it raises soil salinity (UC IPM) and harms soil and plants (OSU Extension article).

A beer trap attracts slugs from only a few feet away (UC IPM).

Step 3: barriers

• Copper. UC IPM uses a vertical strip of copper flashing or screen at least 2 inches tall, buried 1 to 2 inches into the soil, or copper foil or tape around planter boxes, which repels until it tarnishes. Oregon State wraps a 3- to 4-inch band around raised beds or pots (OSU Extension article), or a 3-inch band, with a cone of copper wire spiral for potted plants (OSU EM 9155). The band must be wide enough to cover the whole slug; narrow tape suits only small gardens or containers, and sharp edges can hurt young children (UMN). The Oregon Master Gardeners say most copper sold in garden shops is too narrow.
• Start clean. Make sure no slugs are already inside the barrier (OSU EM 9155). In planter boxes, check that the soil is pest-free and hand-pick any that remain before planting (UC IPM).
• Diatomaceous earth. A dry band 1 inch high and 3 inches wide loses effectiveness when damp, so UC IPM calls it not very useful in most gardens; Oregon State says to reapply after rain or irrigation (OSU EM 9155); Minnesota calls it generally ineffective. Lime, ashes and diatomaceous earth "slow the slugs down, but do not kill them" (Oregon Master Gardeners).
• Eggshells and coffee grounds have not been shown to work (UC IPM).

Step 4: baits, if they are still needed

Baits work best combined with the steps above, will not give long-term control on their own and also kill beneficial snails and slugs (UC IPM). Oregon State lists three active ingredients, metaldehyde, iron phosphate and sodium ferric EDTA, and says all can be harmful to children, pets and wildlife (OSU EM 9155).

• Where. Sprinkle bait, do not pile it, on soil where slugs travel: near but not on the plants they eat, near hiding spots and along paths between shelter and garden (UC IPM). Scatter lightly rather than in piles or bands; more than the label calls for does not work better (OSU Extension article).
• When. Late afternoon or evening (UC IPM, UMN), not before heavy watering, which makes pellets moldy (UC IPM). In Oregon, fall baiting aims to kill slugs "before they lay eggs" (OSU Extension article), and survivors can be controlled in early spring before they resume feeding (OSU EM 9155).
• Keep pets out. Oregon State suggests a bait station: a milk jug or large yogurt container buried on its side with a 2-inch opening (OSU EM 9155). Store baits where pets cannot reach them (NPIC).

This page gives no rates. Follow the product label, which is the law; confirm the crop is listed and observe the pre-harvest interval (UMN); wear the protective gear the label calls for and wash afterward (OSU EM 9155). NPIC says metaldehyde poisoning signs in dogs can appear within minutes to three hours; if a pet eats bait, contact a veterinarian or the ASPCA Animal Poison Control Center (888-426-4435, a fee may apply).

Natural enemies

Ground beetles, toads, snakes, birds and other predators eat slugs; pesticides can harm them, so Minnesota advises spot treatments. UC IPM says they are rarely effective enough on their own. Ducks, geese or chickens penned in an infested area can significantly reduce problems, but seedlings need protecting from them (UC IPM), and chickens can eat collected slugs (OSU EM 9155); see backyard chickens. In Southern California the predatory decollate snail is used against brown garden snails in citrus, but it may be released only in certain counties (UC IPM).

Containers and raised beds

Slugs hide under pots by day, so Oregon State raises pots on bricks or pot feet (OSU Extension article). Copper tape fits around a pot or planter box (UC IPM, UMN). Water in the morning; the container watering guide covers how often.

Where sources differ

Related: cabbage worms and the lettuce page.

Slug and snail checklist

• Slime trails seen, so the damage is slugs or snails, not insects.
• Boards, debris and dense ground cover cleared near beds; pots raised.
• Morning watering at the roots.
• Night hand-picking into soapy water, plus board or beer traps; no salt.
• Copper band wide enough, with no slugs left inside.
• If baiting: product labeled for the crop, scattered lightly in the evening, kept away from pets.