Photo: Snail damage to Black Eyed Susan
A good snail and slug management program relies on a combination of methods. In a nursery or greenhouse, inspect all plants before placing in the growing area. If possible, place in a holding area for 2 days and use an attractive bait containing metaldehyde or a “beer trap” nearby to monitor for snails or slugs that might be in the pots. Eliminate, as much as possible, all places in and around growing areas where snails and slugs can hide during the day. Boards, stones, debris, weedy areas around beds or under benches, leafy branches growing close to the ground, and dense ground covers are ideal sheltering spots. Make a regular practice of trapping, baiting, and removing snails and slugs from these areas. For more information see the Snail and Slug section of the Pest Management Guidelines for Floriculture and Nurseries
Locate susceptible plants as far away from snail and slug hiding places as possible. Reducing hiding places allows fewer snails and slugs to survive. The survivors congregate in the remaining shelters, where you can more easily locate and remove them.
Switching from sprinkler irrigation to drip irrigation will reduce humidity and moist surfaces, making the habitat less favorable for these pests. Copper barriers can be useful for protecting especially susceptible plants. Though baits can be part of a management program, it is better to use them in conjunction with other habitat modification, especially in growing areas that contain plenty of shelter, food, and moisture.
Plant selection can greatly affect how difficult your battle with snails and slugs will be. Because snails and slugs favor seedlings and plants with succulent foliage, you will need to vigilantly protect these. Some plants these pests will seriously damage include basil, dahlia, delphinium, hosta, marigolds, strawberries, and many other vegetable plants. On the other hand, many plants resist snail and slug damage including begonias, California poppy, fuchias, geraniums, impatiens, lantana, nasturtiums, and purple robe cup flower as well as many plants with stiff leaves and highly scented foliage such as lavender, rosemary, and sage. Most ornamental, woody plants, and ornamental grasses also aren’t seriously affected but could serve as hiding places for snails and slugs during the day.
The information in this section has been modified from the University of California IPM website (http://www.ipm.ucanr.edu/)