Controlling snails and slugs

How many times have you wandered into your garden on a cool weekend morning, only to discover telltale slime trails, holes chewed in the leaves of just-planted ornamentals, or vegetable seedlings chewed to the ground? Or worse yet, walked unsuspectingly down a pathway only to smash a slimy slug or crunch a juicy snail beneath your feet?

Common garden snails and slugs are such ubiquitous pests that the battle to control them never ends. This year, soaking rains and lush new plant growth have provided a plentiful selection of tender morsels for them to eat.

Brown garden snail and damage on citrus fruit. (Photo courtesy of the University of California)

Gray garden slugs (Photo by Jack Kelly Clark, UC IPM)

The most common snails and slugs in our California gardens are non-native; in fact, the brown garden snail was originally introduced to the U.S. as food. But, since most folks would rather not snack on them, let’s look at other ways to reduce their population!

Cultural control methods involve eliminating the environmental conditions that snails and slugs prefer. When possible, replace plants susceptible to chewing damage with others that resist the pests, such as California poppy, lantana, lavender, ornamental grasses, rosemary, sages, and stiff-leaved or woody plants. Switch from sprinklers to drip irrigation to minimize excess surface moisture. Watch for dark, damp hiding places and modify them to be less attractive.

One very effective method of reducing snail and slug populations is to hand pick them regularly. It’s best to do this after dark, early in the morning, or after a period of rain or irrigation, since snails and slugs are nocturnal and most active in moist conditions. Picking up snails by their hard shells is relatively easy. Slugs are another matter; when disturbed, they contract their muscles and exude slime to become slippery, almost-impossible-to-grip lumps. Try scooping them up with an old spoon or a latex-gloved hand.

If you find hand-picking too distasteful, try enlisting your children or grandchildren in a nighttime “treasure hunt.” Kids armed with flashlights and a ready-made disposal system (a small pail or zip-closure plastic bag partially filled with soapy water) can turn the search into a fun contest.

Barriers are a method of non-lethal snail and slug control. Copper barriers are most effective at keeping the pests away from treasured plants; the metal reacts with slime secretions to create a shock-like sensation. Buy copper flashing, foil, or mesh, trim it into strips, then wrap it around tree trunks and containers or place it along the edges of planter beds. Copper sulfate (alone or mixed with hydrated lime) can also be brushed on surfaces as a repellant.

Abrasives substances that irritate the muscular “foot” of snails and slugs can also be used as barriers. Simply place dry ashes or food grade diatomaceous earth (DE) on the soil around planting areas, in bands about 3 inches wide. This technique is best used in small garden areas (since the abrasives must be used in relatively large quantities) and in areas that don’t get wet (since they lose their effectiveness when damp). Be sure the area you encircle is free of snails and slugs or you will keep them near the plants you’re trying to protect.

Traps can also be an easy and effective method of control. One approach is to place wooden boards or overturned pots on the ground. Snails and slugs will hide underneath them during the night, and in the morning they can be scraped off and disposed of.

Beer traps are another non-toxic method of attracting and killing snails and slugs, but they have a few disadvantages. They must be cleaned and refilled frequently; they only work within a radius of a few feet, since it’s the odor of fermented sugar that attracts the fleshy pests; and lots of traps are needed to reduce snail/slug populations. Rather than using a perfectly good beverage, make a concoction that will ferment and entice just as effectively as beer. Measure one tablespoon each of yeast, flour, and sugar, mix with one cup of water, and pour into high-walled containers with narrow openings.

Low-toxicity baits are another option for snail and slug control. Pellets or granules containing iron phosphate (Sluggo, Escar-Go) are the safest for children, pets, and wildlife. Sprinkle them around affected plants—do not mound bait in piles—and always follow application instructions.

Avoid poisonous means of snail and slug control whenever possible. Many products contain metaldehyde, which is attractive and very toxic to dogs, cats, birds, and other wildlife. Never place these baits where children or pets can reach them, and do not apply them on or near plants, especially those being grown for food. Don’t use metaldehyde-based products that also contain carbaryl, since it’s toxic to earthworms and other beneficial soil-dwelling organisms.

For more specific information and guidance, see U.C. Integrated Pest Management (IPM) Publication 7427, “Snails and Slugs” (http://ipm.ucanr.edu/PDF/PESTNOTES/pnsnailsslugs.pdf).

For gardening-related questions, call the UC Master Gardener office at 209-953-6112, or use our website.

 

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