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
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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. ones. Because of the potential impact of the decollate snail on certain endangered Figure 8. The devil’s coach horse, Ocy- When using copper bands on planter mollusk species, it can’t be released in pus olens, which is more than an inch boxes, be sure the soil within the boxes California outside of Fresno, Imperial, long, is a predatory beetle that feeds on snails and slugs. is snail free before applying them. If Kern, Los Angeles, Madera, Orange, Riv- it isn’t, handpick the snails and slugs erside, Santa Barbara, San Bernardino, from the soil after applying the band San Diego, Ventura, and Tulare counties. (but before planting new plants) until Decollate snails can feed on seedlings, the box is free of these pests. Solarizing small plants, and flowers and can be a the soil—a technique that uses clear, nuisance when they cover the back patio plastic tarp and the sun’s heat—is a on a misty day. Because snail baits will good way to kill eggs in raised beds. kill decollate snails, you shouldn’t use them where these predators are active. Instead of copper bands, Bordeaux mixture (a copper sulfate and hydrated Baits lime mixture) or copper sulfate alone Snail and slug baits can be effective Figure 9. The decollate snail is a preda- brushed onto trunks will repel snails. when used properly in conjunction tor of snails. One treatment should last about a year. with a cultural program incorporating Adding a commercial spreader or white the other methods discussed above. Baits containing only metaldehyde are latex paint can help the Bordeaux mix- However, baits alone won’t effectively most reliable when temperatures are ture remain effective for two seasons. control snails or slugs. Baits are toxic to warm or during periods of lower hu- all snails and slugs, including the pred- midity. When it is sunny or hot, these Barriers of dry ashes or other abrasives atory decollate snail and native species. baits cause snails and slugs to die from heaped in a band 1 inch high and 3 desiccation or dehydration. The pests inches wide around the garden also can Several types of snail and slug bait prod- usually die with one day of ingesting be effective. However, these barriers lose ucts are available. Baits containing the the chemical or getting it on their foot. their effectiveness after becoming damp, active ingredient metaldehyde are most If cool, wet weather follows the bait- making them difficult to maintain and common; however, metaldehyde baits ing, they can recover if they ingest a not very useful in most garden situations. are particularly poisonous to dogs and sublethal dose. Don’t water heavily for cats, and the pelleted form is especially at least 3 or 4 days after bait placement, Natural Enemies attractive to dogs. Don’t use metaldehyde since watering will reduce effectiveness. Snails and slugs have many natural en- snail baits where children and pets could Most metaldehyde baits break down emies including ground beetles, patho- encounter them. Metaldehyde baits con- rapidly when exposed to sunlight and gens, snakes, toads, turtles, and birds, taining 4% active ingredient are more high irrigation; however, some paste or but most are rarely effective enough effective than those containing only 2%; bullet formulations (e.g. Deadline) hold to provide satisfactory control in the however, they also are more toxic to dogs up somewhat longer in these conditions. garden. One predator found in some and wildlife. Avoid getting metaldehyde California gardens is a large Staphyli- bait on plants, especially vegetables. Iron phosphate baits—available under nid beetle called the devil’s coach horse, many trade names including Sluggo Ocypus olens (Fig. 8). However, this Some metaldehyde products are formu- and Escar-Go—have the advantage beetle, which is more than 1-inch long, lated with carbaryl, partly to increase of being safe for use around children, also will feed on ripening or decaying the spectrum of pests controlled such domestic animals, birds, fish, and other fruits and vegetables. as soil- and debris-dwelling insects, spi- wildlife, making them a good choice ders, and sowbugs. However, carbaryl for an integrated pest management Domesticated fowl—such as ducks, is toxic to earthworms and soil-inhab- program in your garden. Ingesting geese, or chickens—kept penned in iting beneficial insects such as ground even small amounts of the bait will infested areas can be effective snail beetles, so it is better to avoid using cause snails and slugs to stop feeding, predators that significantly reduce snail baits containing carbaryl. although it can take several days for
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the snails to die. You can scatter the and Native Fauna of California. Oakland: bait on lawns or on the soil around any Univ. Calif. Agric. Nat. Res. Publ. 8336. vegetable, ornamental, or fruit tree that needs protection. Iron phosphate baits Sakovich, N. J., J. B. Bailey, and T. W. can be more effective against snails Fisher. 1984. Decollate Snails for Con- than slugs overall and more effective trol of Brown Garden Snails in Southern than metaldehyde during periods of California Citrus Groves. Oakland: Univ. higher humidity. Snails and slugs tend Calif. Agric. Nat. Res. Publ. 21384. v to hide before they die, so you won’t see scattered empty shells or dead snails and slugs as you would if treat- ing them with metaldehyde.
Sprinkle baits in areas that snails and slugs regularly frequent such as around sprinkler heads. Placing baits repeated- AUTHORS: M. L. Flint, UC Statewide IPM University of California scientists and other ly in the same areas maximizes control, Program, Davis/Entomology, UC Davis; and qualified professionals have anonymously peer reviewed this publication for technical accuracy. The because mollusks tend to return to food C. A. Wilen, UC Statewide IPM Program, ANR Associate Editor for Urban Pest Management source sites. Never pile bait in mounds San Diego Co. managed this review process. or clumps, especially those products To simplify information, trade names of products EDITOR: M. L. Fayard have been used. No endorsement of named products that are more hazardous, because pil- is intended, nor is criticism implied of similar products ing makes bait attractive to pets and ILLUSTRATIONS: Figs. 1, 3–7 and 9, J, that are not mentioned. This material is partially based upon work children and is not as effective as sprin- K. Clark, Fig. 2, D. Rosen; and Fig. 8, R. supported by the Extension Service, U.S. Department kling. Thick, liquid baits might persist Weinstein. of Agriculture, under special project Section 3(d), better when it is rainy or in areas that Integrated Pest Management. receive sprinkler irrigation. Produced by UC Statewide Integrated Pest Management Program The timing of any baiting is critical; bait- University of California, Davis, CA 95616 ing is less effective during very hot, very This and other Pest Notes are available at dry, or cold times of the year, because www.ipm.ucdavis.edu. snails and slugs are less active during For more information, contact the University of these periods. Irrigate before applying a California Cooperative Extension office in your bait to promote snail activity, and apply county. See your telephone directory for addresses University of California the bait in the late afternoon or evening. and phone numbers, or visit http://ucanr.org/ce.cfm. Agriculture and Natural Resources Program Sprinkle bait around sprinklers, close to walls and fences, or in other moist and WARNING ON THE USE OF CHEMICALS Pesticides are poisonous. Always read and carefully follow all precautions and safety recommendations protected locations, or scatter it along given on the container label. Store all chemicals in the original, labeled containers in a locked cabinet or shed, areas that snails and slugs cross to get away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock. from sheltered areas to the garden. Pesticides applied in your home and landscape can move and contaminate creeks, rivers, and oceans. Confine chemicals to the property being treated. Avoid drift onto neighboring properties, especially gardens containing fruits or vegetables ready to be picked. REFERENCES Do not place containers containing pesticide in the trash or pour pesticides down the sink or toilet. Either use the pesticide according to the label, or take unwanted pesticides to a Household Hazardous Waste Collection Dreistadt, S. H., J. K. Clark, and M. L. site. Contact your county agricultural commissioner for additional information on safe container disposal and Flint. 1994. Pests of Landscape Trees and for the location of the Household Hazardous Waste Collection site nearest you. Dispose of empty containers by following label directions. Never reuse or burn the containers or dispose of them in such a manner that Shrubs: An Integrated Pest Management they may contaminate water supplies or natural waterways. Guide. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3359. NONDISCRIMINATION STATEMENT The University of California prohibits discrimination or harassment of any person on the basis of race, color, national origin, religion, sex, gender identity, pregnancy (including childbirth and medical conditions Flint, M. L. 1998. Pests of the Garden and related to pregnancy or childbirth), physical or mental disability, medical condition (cancer-related or Small Farm: A Grower’s Guide to Using genetic characteristics), ancestry, marital status, age, sexual orientation, citizenship, or service in the uniformed services (as defined by the Uniformed Services Employment and Reemployment Rights Act of Less Pesticide. 2nd ed. Oakland: Univ. 1994: service in the uniformed services includes membership, application for membership, performance of Calif. Agric. Nat. Res. Publ. 3332. service, application for service, or obligation for service in the uniformed services) in any of its programs or activities. University policy also prohibits reprisal or retaliation against any person in any of its programs or activities Koehler, C. and W. Barclay. 1983. Snail for making a complaint of discrimination or sexual harassment or for using or participating in the investigation Barriers. California Agriculture 37(9-10):15. or resolution process of any such complaint. University policy is intended to be consistent with the provisions of applicable State and Federal laws. Inquiries regarding the University’s nondiscrimination policies may be directed to the Affirmative Action/ McDonnell, R., T. Paine, and M. J. Gor- Equal Opportunity Director, University of California, Agriculture and Natural Resources, 1111 Franklin Street, mally. 2009. Slugs: A Guide to the Invasive 6th Floor, Oakland, CA 94607, (510) 987-0096.
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