Snail and slug baits can be effective when used properly in conjunction with a cultural program incorporating the other methods discussed above. However, baits alone won’t effectively control snails or slugs. Baits are toxic to all snails and slugs, including the predatory decollate snail and native species.
Movie: How to apply snail and slug bait (1:24 min) (Note: This is directed toward residential applications)
Several types of snail and slug bait products are available. Baits containing the active ingredient metaldehyde are most common; however, metaldehyde baits are particularly poisonous to dogs and cats, and the pelleted form is especially attractive to dogs. In production nurseries, this is usually not a problem but growers should be aware of these risks. Metaldehyde baits containing 4% active ingredient are more effective than those containing only 2%. Metaldehyde baits are most effective when applied to moist soil. Higher application rates should be used if the pest population is high and can be reduced as the pest population is reduced.
Baits containing only metaldehyde are most reliable when temperatures are warm or during periods of lower humidity. When it is sunny or hot, these baits cause snails and slugs to die from desiccation or dehydration. The pests usually die with one day of ingesting the chemical or getting it on their foot. If cool, wet weather follows the baiting, they can recover if they ingest a sublethal dose. Don’t water heavily for at least 3 or 4 days after bait placement, since watering will reduce effectiveness. Most metaldehyde baits break down rapidly when exposed to sunlight and high irrigation; however, formulations hold up somewhat longer in these conditions.
Iron phosphate baits—available under many trade names including Sluggo—have the advantage of being safe for use around children, domestic animals, birds, fish, and other wildlife, making them a good choice for an integrated pest management program. Ingesting even small amounts of the bait will cause snails and slugs to stop feeding, although it can take several days for the snails to die. You can scatter the bait on lawns or on the soil around any vegetable, ornamental, or fruit tree that needs protection. Iron phosphate baits can be more effective than metaldehyde during periods of higher humidity. Snails and slugs tend to hide before they die, so you won’t see scattered empty shells or dead snails and slugs as you would if treating them with metaldehyde.
Photo: Iron phosphate bait sprinkled in a snail prone area
Sprinkle baits in areas that snails and slugs regularly frequent such as around sprinkler heads. Placing baits repeatedly in the same areas maximizes control, because mollusks tend to return to food source sites. Never pile bait in mounds or clumps, especially those products that are more hazardous, because piling makes bait attractive to pets and children and is not as effective as sprinkling. Thick, liquid baits might persist better when it is rainy or in areas that receive sprinkler irrigation.
The timing of any baiting is critical; baiting is less effective during very hot, very dry, or cold times of the year, because snails and slugs are less active during these periods. Irrigate before applying a bait to promote snail activity, and apply the bait in the late afternoon or evening. Sprinkle bait around sprinklers, or in other moist and protected locations, or scatter it along areas that snails and slugs cross to get from sheltered areas to the beds.
In situations where action must be taken to control snails and slugs in a nursery or greenhouse that is designated snail-free or has other limitations, methiocarb (Mesurol) my be recommended. This is a sprayable molluscicide, is labeled "Danger", and can only be used two times per crop per year. This product is very effective and fast acting, but due to its high toxicity and label restrictions should only be used as a "rescue" treatment.
The information in this section has been modified from the University of California IPM website (http://www.ipm.ucanr.edu/).