How to Manage Pests
UC Pest Management Guidelines
Brown Garden Snail
Scientific Name: Cantareus aspersus (= Helix aspersa)
(Reviewed 9/08, updated 9/08)
In this Guideline:
Description of the Pest
The brown garden snail is about 1 inch (2.5 cm) in diameter at maturity and has a distinct brown and gray color pattern. It is most active during the night and early morning when it is damp. In southern California, particularly along the coast, young snails are active throughout the year; in the San Joaquin Valley brown garden snails are active primarily in late winter and spring. Mature snails hibernate in the topsoil during winter.
Snails are bisexual (hermaphroditic); all snails of reproductive age lay eggs up to six times during a season, depending on local climate and available moisture. After mating, they lay up to 80 eggs a month in shallow depressions in the topsoil. Eggs are white, spherical, and about 0.1 inch (3 mm) in diameter.
The brown garden snail can cause extensive damage in orchards by feeding on ripe and ripening fruit, leaves of young trees, and in nurseries by feeding on young tree bark. Fruit damage appears as circular chewed areas in the rind. Damaged leaves have large chewed areas along the margins. Snails can cause severe problems in citrus orchards, where no-till weed control and sprinkler and low-volume irrigation create an ideal environment for snail development.
Management of the brown garden snail is a multi-step process that involves pruning tree skirts to make it more difficult for snails to attack low-hanging fruit; banding tree trunks with copper foil or a basic copper sulfate slurry to prevent snails from climbing trees, and putting out poison bait or spraying the foliage to reduce their populations. Alternatively, growers can make releases of the predatory decollate snails, but this option should not be employed in groves where poison baits are used because baits kill both the pest and predator snails.
While not always consistently effective, the decollate snail, Rumina decollata, may reduce brown garden snail populations to insignificant levels in 4 to 10 years. The most effective way to manage brown garden snails while establishing the decollate snail is to combine skirt pruning and trunk banding with decollate snail releases. Decollate snails do not climb trees, thus they will not be affected by pruning or trunk banding.
To establish the decollate snail, distribute about 8 to 10 decollate snails to the shady northeast skirt zone of every other tree in every other row. (If a shorter transition period is desired, release a larger number of snails per tree.) If there are not enough snails to release at this rate, a second method is to reduce brown garden snails by mechanical removal or with a poison bait program. Release the available decollate snails in a cluster of untreated core trees. After the colony grows, some of the snails can be transferred to other trees in the grove. Provide an unbaited buffer zone of at least two tree rows between the expanding colony and the baited areas or the decollate snail will feed on poison bait and die. When establishing decollate snails in a core area, provide supplemental food, such as rabbit pellets, and cover for them to hide under, such as old fertilizer bags. The best time to introduce decollate snails is when it is warm and damp (February through May); this snail will survive well in hot areas, but avoid introducing them during the hot, dry season as they must have moist soil conditions to move about effectively and to establish themselves.
The rate of decollate snail dispersal depends on the amount of moisture present. Low-volume and sprinkler irrigation are most conducive to snail movement and development. Light supplemental irrigations may be desirable during the establishment of a colony. It is more difficult to establish decollate snails in groves that are irrigated by furrow.
In addition to moisture, factors that may affect the decollate snails ability to become established in an orchard are the amount of canopy shading the soil (older trees have a larger canopy and thus provide greater shading) and soil texture (coarse sandy soils not only tend to hold less water than loamy soils but also are less preferred by the snails for burrowing).
Prune tree skirts 24 to 30 inches above the ground before the rainy season and apply a barrier trunk treatment. Barrier trunk treatments can be made with a band of copper foil wrapped around the trunk, which repel snails for several years; with an annual application of a Bordeaux slurry that is painted around the trunk; or with an application of a sticky material that contains tribasic copper sulfate. The sticky material also reduces tree access by ants and Fuller rose beetle.
Organically Acceptable Methods
Skirt pruning, trunk banding, releases of decollate snails, and the use of ducks.
Apply bait only to reduce snail populations to low levels before introduction of the decollate snail. Bait immediately following an irrigation or rainy period when the soil is wet and snails are active. The waiting period before the decollate snail can be released following a baiting program depends on soil moisture. Under sprinkler or low-volume irrigation, the toxins will break down faster than in drier soil, and a decollate snail release program can start in about 2 months.
Bait is consumed most easily by snails if it is applied under trees, but unless snails are exposed to the sun and dry conditions, the bait will not be as effective. Snails move around a lot more under humid, moist conditions than under dry conditions. When it is humid and moist, place bait in a narrow strip in the middle between rows; under drier conditions, place bait closer to the ground that is moistened by irrigation.
When snails are present in the trees, a foliar treatment may be necessary.
UC IPM Pest Management Guidelines:
Insects, Mites, and Snails
Acknowledgments for contributions to Insect, Mites, and Snails: