Pest Notes, Publication 7427 Revised March 2018 Integrated Pest Management for Home Gardeners and Landscape Professionals Snails and Slugs nails and slugs are among the most destructive Spests found in gardens and landscapes. The brown garden snail, Cornu aspersum (formerly Helix aspersa), is the most common snail causing problems in California gardens (Figure 1). It was introduced from France during the 1850s for Figure 1. Brown garden snail, Cornu aspersum. use as food. Another damaging snail is the white along on a muscular “foot.” This muscle garden snail, Theba pisana (Figure 2). It constantly secretes mucus, which facil- is currently an established pest only in itates their movement and later dries to San Diego County but has been found form the silvery slime trail that signals in Los Angeles and Orange counties the recent presence of either pest. as well. All land slugs and snails are hermaph- Common species of slugs that injure rodites, so all are able to lay eggs after landscape plants include: the gray mating with another individual. Adult garden slug, Deroceras reticulatum brown garden snails lay an average of (formerly Agriolimax reticulatus) 80 spherical, pearly white eggs at a time (Figure 3); the banded slug, Lehmannia (Figure 5) into a hole in the soil. They poirieri; the three-band garden slug, can lay eggs up to 6 times a year. Darker L. valentiana; the tawny slug, Limacus colored eggs are close to hatching. It flavus (Figure 4); and the greenhouse takes about 2 years for snails to mature. Figure 2. Adult white garden snail, slug, Milax gagates. Slugs reach maturity after about 3 to Theba pisana. 6 months, depending on the species, IDENTIFICATION AND and lay translucent oval to round eggs BIOLOGY in batches of 3 to 40 beneath leaves, in soil cracks, and in other protected Both snails and slugs are members of areas. the mollusk phylum and are similar in structure and biology, except that Snails and slugs are most active at night slugs lack the snail’s external spiral and on cloudy or foggy days. On sunny shell. These mollusks move by gliding days, they seek hiding places out of the heat and bright light. Often the only clues to their presence are their silvery Authors: trails and plant damage. Cheryl A. Wilen, UC IPM Program/ During cold weather, snails and slugs UC Cooperative Extension, San Diego hibernate in the topsoil. In areas with County. mild winters, such as southern coastal Mary Louise Flint, Extension locations, snails and slugs can be active Figure 3. Gray garden slugs, Entomologist Emerita, Entomology, throughout the year. During hot, dry Deroceras reticulatum, with UC Davis. periods snails estivate (hibernation chewing damage and slime trails during hot weather) by sealing them- on leaves. Pest Notes: Snails and Slugs Page 2 of 6 eggs are detected in the bed or garden, shallow cultivation will bring them to the soil surface to dry out. Susceptible and resistant plants. Plant selection can greatly affect how difficult your battle with snails and slugs will be. Because snails and slugs favor seedlings and plants with succu- lent foliage, you will need to vigilantly protect them. Some plants these pests will seriously damage include basil, beans, cabbage, dahlia, delphinium, hosta, lettuce, marigolds, strawberries, Figure 4. Tawny slug, Limacus Figure 5. Snail eggs. and many other vegetable plants. flavus, also called yellow cellar slug. Choose plants that are not attractive to snails and slugs for areas where they selves off with a parchment-like mem- trunks, leafy branches growing close to are dense. Examples are plants with brane. They often attach themselves to the ground, and dense ground covers, highly scented foliage, such as lav- tree trunks, fences, or walls. such as ivy, are ideal sheltering spots. ender, rosemary, and sage and some commonly grown plants including Though baits can be part of a manage- ferns, cyclamen, hydrangea, California DAMAGE ment program, it is best to use them in poppy, nasturtium, and lantana. Snails and slugs feed on a variety of conjunction with habitat modification, Most ornamental woody plants and or- living plants and on decaying plant especially in gardens that contain plen- namental grasses are also not seriously matter. They create irregular holes with ty of shelter, food, and moisture. damaged by snails and slugs but can smooth edges on leaves and flowers by be a hiding place for them during the scraping with their rasp-like tongues. Cultural Control day. Nevertheless, if you design your Small succulent plant parts are easily It will not be possible to eliminate some landscape using snail- and slug-resis- clipped by snail and slug feeding. shelters, such as low ledges on fences, tant plants, you are likely to have very Because they prefer succulent foliage the undersides of wooden decks, and limited damage. or flowers, snails and slugs are primar- water meter boxes, so make a regular Hand-picking. Hand-picking can be ily pests of seedlings and herbaceous practice of trapping and removing very effective if done thoroughly on a plants. They are also serious pests of snails and slugs from these areas. regular basis. At first you should look turfgrass seedlings and ripening fruits Place vegetable gardens or susceptible for snails and slugs daily, paying careful that are close to the ground, such as plants as far away from snail and slug attention to potential hiding places. strawberries and tomatoes. Snails and hiding areas as possible. Reducing hid- After the population has noticeably slugs will also feed on the young plant ing places allows fewer snails and slugs declined, weekly hand-picking can be bark and foliage and fruit of some trees. to survive. The survivors congregate in sufficient. Citrus are especially susceptible to the remaining shelters, where you can damage. more easily locate and remove them. To draw out snails and slugs, water the infested area in the late afternoon. Snail and slug damage can be confused Switching from sprinkler irrigation to After dark, search them out using a with feeding by other pests such as drip irrigation will reduce humidity flashlight, pick them up (rubber or earwigs, caterpillars, or other chewing and moist surfaces, making the habitat latex gloves are recommended), place insects. Look for silvery mucous trails less favorable for these pests. Irrigating them in a plastic bag, and seal and dis- to confirm that slugs or snails caused near sunrise will reduce the amount of pose of them in the trash. You also can the damage, rather than other pests. time that foliage and ground are moist. put them in a bucket with soapy water or diluted ammonia (5 to 10% solu- Solarizing the soil—a technique that MANAGEMENT tion) and dispose of them after they uses a clear plastic tarp and the sun’s are dead. Alternatively, crush captured A good snail and slug management heat—is a good way to kill eggs in snails and leave them in the garden. program relies on a combination of raised beds. See the Pest Notes: Soil So- methods. The first step is to eliminate, larization for Gardens and Landscapes Traps. You can trap snails and slugs as much as possible, all places where for more information. Eggs will also beneath boards or flower pots that you they can hide during the day. Boards, rapidly dry if on the soil surface. If snail position throughout the garden and stones, debris, weedy areas around tree Pest Notes: Snails and Slugs Page 3 of 6 Figure 6. This turned-over board trap reveals Figure 7. Bury beer traps at ground level. snails on its underside. landscape. Inverted melon rinds also Barriers. Several types of barriers will repel snails until it becomes tarnished make good traps. Construct wooden keep snails and slugs out of planting (Figure 8). If the bands do tarnish, you traps using 12- by 15-inch boards (or beds. The easiest to maintain are those can clean them with a vinegar solution. any easy-to-handle size) raised off the made with copper flashing and screen. ground by 1-inch runners (Figure 6). It is believed that copper barriers are When banding tree trunks, wrap the The runners make it easy for the pests effective because the copper reacts copper foil around the trunk and cut it to crawl underneath. with the slime that snails and slugs to allow an 8-inch overlap. Attach one secrete, causing a disruption in their end or the middle of the band to the Scrape off the accumulated snails nervous system similar to an electric trunk with one staple oriented parallel and slugs daily and destroy them (see shock. to the trunk. Overlap and fasten the hand-picking). Do not use salt to de- ends with one or two large paper clips stroy snails and slugs, as it will increase When erecting vertical copper screens, to allow the copper band to slide as the soil salinity. it is best to use a strip that is at least 2 trunk grows. inches tall so you can bury a portion of Some people use beer-baited traps bur- it 1 to 2 inches below the soil to pre- When using copper bands on planter ied at ground level to catch and drown vent slugs from crawling beneath the boxes, be sure the soil within the boxes slugs and snails that fall into them. barrier. is snail-free before applying them. Because it is the fermented part of the If this is not the case, hand-pick and product that attracts these pests, you Copper foil or tape wrapped around remove any snails and slugs that are can also use a sugar-water and yeast planting boxes, headers, or trunks will present after applying the band (but mixture instead of beer (see Cranshaw, 1997).