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Least-Toxic Control of Snails and Slugs Choose a different pests

Factsheet: Beyond Slime: The Least toxic Control of Snails and Slugs

Identification

Pest type: Animals

Slugs and snails are mollusks. They are more closely related to oysters and squid than insects or earthworms, so common insecticides are often useless. There is an incredible diversity of slugs and snails. Some are predatory, some herbivorous, some live on land and some are aquatic. Slugs are closely related to snails; the main difference being the shell. A snail can barricade itself inside its shell, protecting it from drying out and from predators. While slugs do not have the protection of a shell, they also don’t have its physical restraints, allowing them to squeeze through the tiniest spaces. To conserve moisture slugs will shelter in the soil or under debris during hot dry periods.

Is it a problem?

Irregular holes in the leaves of your plants can have plenty of different causes, but the silvery trails of slime mean you have a slug or snail problem. Slugs and snails will destroy the leaves of established plants, but they prefer seedlings. They also feed on many fruits and vegetables prior to harvest, creating wounds in produce that makes it vulnerable to fungi and other diseases. Slugs can be most damaging in moist environments. If your plants are starting to get holes in them, you may have a slug or snail problem. To be sure, check plants at night with a flashlight, paying attention to easy-to-miss places like the backs of leaves.

Pest prevention practices

Remove sources of water/moisture
Remove potential habitat
Foster natural resilience

Clear away debris that may provide shelter, including wood piles, empty flower pots, and certain ground covers such as ivy.

Water your plants in the morning instead of at night. On farms, using drip irrigation - in addition to being efficient - can also help control snail and slug populations on farms and in gardens.

Plant crops that slugs find unpalatable, such as ginger, garlic, mint, chives, red lettuce, red cabbage, sage, sunflower, fennel, foxglove, mint, chicory and endive.

In-Depth Information:
The best way to prevent or control a slug or snail infestation is to reduce moisture, though it may take some time before you see results. Slugs and snails lack an insect’s hard exoskeleton. Instead they require water to secrete a protective mucus or slime.

Drip irrigation, also called trickle or micro irrigation, involves systems that slowly drip water directly on to the roots of a plant. Modern drip irrigation uses tubing or drip tape to channel water directly to crops. Compared to traditional irrigation where water is sprayed or allowed to flow over an entire field, resulting in losses from runoff and evaporation.

Plants that slugs find unpalatable can be placed around the perimeter of your garden to ward off infestation. An alternative route is placing sacrifice plants such as marigolds to attract slugs away from higher value crops. Reconsidered the type of mulch you are using - straw and wood chips, in particular can retain moisture and attract slugs.

Monitoring and record-keeping

Slug and snail monitoring should be part of all gardeners routine checks. Counting gastropods 7 days after controls have been applied provides an indication of success or otherwise. Monitoring prior to infestation may also give some indication of threshold levels requiring more than just hand picking.

Non-chemical and mechanical controls

Create a barrier
Remove debris and habitat
Handpick and destroy

In-Depth Information:
Slow moving snails and slugs are easy to hand pick when they can be found. (To kill them you can drop them into a container of soapy water. Do not put dead slugs in the compost pile, they will give off a strong odor. Put dead slugs in a sealed container and throw them in the trash.) Trapping slugs can be as simple as providing a shady space for them to shelter during the day, such as an overturned flower pot, or board placed on the soil between plant rows. Check your traps in the morning and dispose of pests.

More elaborate traps, like the Snailer or the Slug Saloon can be bought from garden stores or online. You can also make a trap using a coffee can with a hole cut into the side about halfway up. Bury the can halfway so the hole is at ground level. Make a simple bread dough with flour, water and yeast to act as bait. Place some in the can alongside a few inches of water. Slugs and snails are highly attracted to the bread dough, and will drown when submerged in water. The trap should be checked daily, and the bread dough should be changed out at least every 8 days.

Slugs and snails will avoid crossing over acidic, basic or abrasive materials. Ash or diatomaceous earth can be used to create a barrier; however these materials are less effective when wet. Copper bands or foils also create effective barriers to snails and slugs. The copper reacts with their mucus creating an electric shock. A copper band around a potted plant container will keep slugs and snails away. Just be sure there aren’t any slugs or snails already in the container or you will be trapping the pest in with your plants.

Biological controls

Snails and slugs also have many natural enemies including ground beetles, pathogens, snakes, toads, turtles, and birds, but most are rarely effective enough to provide satisfactory control in the garden. However, domesticated fowl—such as ducks, geese, or chickens—kept penned in infested areas can be effective snail predators that significantly reduce problems. Be careful, though, as these birds also can eat seedlings.

Although not yet registered in the US, research shows that a nematode long used in Europe to control slug and snail populations is likely also native to North America.

Least-toxic chemical options as a last resort

Table salt sprinkled on a slug can be very effective, but be careful, because it can also damage plants.
Caffeine is also an effective molluscicide. Scientists believe it acts as a neurotoxin. Concentrations of 1-2% are enough to kill slugs; however, such a high concentration can also damage plants. A much weaker concentration can still prevent feeding, without damaging crops. Caffeine, however, is not registered by EPA, so it is not available in commercial pesticides. A cup of instant coffee contains about .05% caffeine.
Many organic molluscicides contain Iron Phosphate. Iron phosphate when used properly is regarded as safe by EPA. It is the same compound found in vitamin supplements. However some commercially available and allowed for use in organic production can contain inert ingredients that have hazardous properties.

Garlic oil

Chemicals to Avoid

Look at your product labels and try to avoid products containing those chemicals listed below:

(A = acute health effects, C = chronic health effects, SW = surface water contaminant, GW = ground water contaminant, W = wildlife poison, B = bee poison, LT = long-range transport)

Carbaryl (A, C, SW, GW, W, B)

Copper Sulfate (W)

Metaldehyde (A, C, W)

Spinosad (C, W, B)

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