SNAILS AND SLUGS Integrated Pest Management for Home Gardeners and Landscape Professionals Snails and slugs are among the most Snails and slugs are most active at bothersome pests in many gardens and night and on cloudy or foggy days. On landscapes. The brown garden snail, Cor- sunny days they seek hiding places out nu aspersum (formerly Helix aspersa), is the of the heat and bright light. Often the most common snail causing problems in only clues to their presence are their California gardens (Fig. 1). It was intro- silvery trails and plant damage. In duced from France during the 1850s for areas with mild winters, such as south- use as food. Another troublesome snail is ern coastal locations, snails and slugs the white garden snail, Theba pisana (Fig. can be active throughout the year. 2). It currently is established only in San Diego County but has been found in Los During cold weather, snails and slugs Figure 1. Brown garden snail. Angeles and Orange counties as well. hibernate in the topsoil. During hot, dry periods or when it is cold, snails Several species of slugs also cause seal themselves off with a parchment- damage including the gray garden slug like membrane and often attach them- (Deroceras reticulatum, formerly Agrio- selves to tree trunks, fences, or walls. limax meticulatus) (Fig. 3), the banded slug (Lehmannia poirieri), the three-band DAMAGE garden slug (L. valentiana), the tawny Snails and slugs feed on a variety of liv- slug (Limacus flavus) (Fig. 4), and the ing plants and on decaying plant matter. greenhouse slug (Milax gagates). They chew irregular holes with smooth edges in leaves and flowers and can clip Figure 2. Adult white garden snail, Theba pisana. IDENTIFICATION AND succulent plant parts. They also can BIOLOGY chew fruit and young plant bark. Both snails and slugs are members of the mollusk phylum and are similar in Because they prefer succulent foliage or structure and biology, except slugs lack flowers, they primarily are pests of seed- the snail’s external, spiral shell. These lings and herbaceous plants, but they mollusks move by gliding along on a also are serious pests of ripening fruits muscular “foot.” This muscle constant- that are close to the ground such as ly secretes mucus, which facilitates strawberries, artichokes, and tomatoes. their movement and later dries to form They also will feed on foliage and fruit the silvery “slime trail” that signals the of some trees; citrus are especially sus- presence of either pest. ceptible to damage. Look for the silvery Figure 3. Gray garden slugs with chew- mucous trails to confirm slugs or snails ing damage and slime trails on leaves. All land slugs and snails are hermaph- caused the damage and not earwigs, rodites, so all have the potential to lay caterpillars, or other chewing insects. eggs. Adult brown garden snails lay an average of 80 spherical, pearly white MANAGEMENT eggs (Fig. 5) at a time into a hole in the A good snail and slug management pro- soil. They can lay eggs up to 6 times a gram relies on a combination of methods. year, and it takes about 2 years for snails The first step is to eliminate, as much as to mature. Slugs reach maturity after possible, all places where they can hide about 3 to 6 months, depending on the during the day. Boards, stones, debris, species, and lay clear, oval to round eggs weedy areas around tree trunks, leafy in batches of 3 to 40 beneath leaves, in branches growing close to the ground, Figure 4. Tawny slug, also called yellow soil cracks, and in other protected areas. and dense ground covers such as ivy are cellar slug. EST OTES Publication 7427 PUniversity of California N Statewide Integrated Pest Management Program Agriculture and Natural Resources November 2009 November 2009 Snails and Slugs ideal sheltering spots. It won’t be possible to potential hiding places. After the to eliminate some shelters such as low population has noticeably declined, a ledges on fences, the undersides of wood- weekly handpicking can be sufficient. en decks, and water meter boxes, so make a regular practice of trapping and remov- To draw out snails and slugs, water the ing snails and slugs from these areas. infested area in the late afternoon. After dark, search them out using a flashlight, Locate vegetable gardens or susceptible pick them up (rubber gloves are handy plants as far away from snail and slug when slugs are involved), place them in hiding places as possible. Reducing hid- a plastic bag, and dispose of them in the ing places allows fewer snails and slugs Figure 5. Snail eggs. trash. You also can put them in a bucket to survive. The survivors congregate in with soapy water and dispose of them the remaining shelters, where you can more easily locate and remove them. in your compost pile after they are dead. Alternatively, crush captured snails Switching from sprinkler irrigation to and slugs and leave them in the garden. drip irrigation will reduce humidity and Another option for killing slugs you moist surfaces, making the habitat less have collected is to spray them with a favorable for these pests. Choose snail- solution of household ammonia diluted proof plants, such as those listed below, to a 5 to 10% solution in water. for areas where snails and slugs are dense. Copper barriers can be useful for Traps Figure 6. This turned over board trap protecting especially susceptible plants. You can trap snails and slugs beneath reveals snails on its underside. Though baits can be part of a manage- boards or flower pots that you position ment program, it is better to use them in throughout the garden and landscape. conjunction with other habitat modifica- tion, especially in gardens that contain Inverted melon rinds also make good plenty of shelter, food, and moisture. traps. Construct wooden traps using 12- by 15-inch boards (or any easy-to-han- Plant selection can greatly affect how dle size) raised off the ground by 1-inch difficult your battle with snails and runners (Fig. 6). The runners make it slugs will be. Because snails and slugs easy for the pests to crawl underneath. favor seedlings and plants with succu- Scrape off the accumulated snails and lent foliage, you will need to vigilantly slugs daily and destroy them; crushing protect these. Some plants these pests is the most common method. Don’t use Figure 7. Copper barriers can keep snails will seriously damage include basil, salt to destroy snails and slugs, since it and slugs out of trees and raised beds. beans, cabbage, dahlia, delphinium, will increase soil salinity. hosta, lettuce, marigolds, strawberries, Barriers and many other vegetable plants. On the Some people use beer-baited traps Several types of barriers will keep other hand, many plants resist snail and buried at ground level to catch and snails and slugs out of planting beds. slug damage including begonias, Cali- drown slugs and snails that fall into The easiest to maintain are those made fornia poppy, fuchias, geraniums, impa- them. Because it is the fermented part with copper flashing and screen. It is tiens, lantana, nasturtiums, and purple of the product that attracts these pests, believed that copper barriers are effec- robe cup flower as well as many plants tive because the copper reacts with the with stiff leaves and highly scented foli- you also can use a sugar-water and yeast mixture instead of beer. However, slime that snails and slugs secrete, caus- age such as lavender, rosemary, and sage. ing a disruption in their nervous system these traps aren’t very effective for the Most ornamental, woody plants, and similar to an electric shock. When erect- labor involved. Beer traps attract slugs ornamental grasses also aren’t seriously ing vertical copper screens, it is best to and snails within an area of only a few affected. If you design your landscape use ones that are at least 4 inches tall, so using snail and slug resistant plants, you feet, and you must replenish the bait you can bury a portion of it a few inches are likely to have very limited damage. every few days to keep the level deep below the soil to prevent slugs from enough to drown the mollusks. Traps crawling beneath the barrier. Handpicking must have deep, vertical sides to keep Handpicking can be very effective if the snails and slugs from crawling out Copper foil (e.g. Snail-Barr) wrapped done thoroughly on a regular basis. and a top to reduce evaporation. You around planting boxes, headers, or trunks At first you should look for snails and can purchase this type of snail and (Fig. 7) will repel snails for several years. slugs daily, paying careful attention slug trap at garden supply stores. When banding trunks, wrap the copper ◆ 2 of 4 ◆ November 2009 Snails and Slugs foil around the trunk, tab side down, and problems. Be careful, though, as these cut it to allow an 8-inch overlap. Attach birds also can eat seedlings. one end or the middle of the band to the trunk with one staple oriented parallel to The predatory decollate snail, Rumina de- the trunk. Overlap and fasten the ends collata, (Fig. 9) has been released in South- with one or two large paper clips to al- ern California citrus orchards to control low the copper band to slide as the trunk young brown garden snails and is pro- grows. Bend the tabs out at a 90° angle viding very effective biological control. It from the trunk. If the bands tarnish, you feeds only on small snails, not full-sized can clean them with a vinegar solution.