How to Manage Pests

UC Pest Management Guidelines

Citrus

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.

Damage

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

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.

Biological Control

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).

Cultural Control

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.

Treatment Decisions

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.

Common name Amount to use R.E.I.‡ P.H.I.‡
(example trade name) (type of coverage)** (hours) (days)

  Calculate impact of pesticide on air quality
 
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy and impact on natural enemies and honey bees. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. RUMINA DECOLLATA#   NA NA
  (Decollate Snail)
  RANGE OF ACTIVITY: Pests: narrow (brown garden snail); Natural enemies: none
  PERSISTENCE: Pests: long, unless snail bait used; Natural enemies: none
  COMMENTS: May take several seasons to obtain control. These snails may be released only in the following California counties: Fresno, Kern, Imperial, Los Angeles, Madera, Orange, Riverside, San Bernardino, San Diego, Santa Barbara, Tulare, and Ventura.
 
B. COPPER BANDS#   NA NA
  RANGE OF ACTIVITY: Pests: narrow (brown garden snail only); Natural enemies: none
  PERSISTENCE: Pests: long; Natural enemies: none
  COMMENTS: Use with skirt pruning. Affix a copper foil band around the tree trunk at a height of 1–2 feet above the ground. It is essential that the copper foil be affixed to the tree trunk with about an 8-inch overlap so it will slip and allow for trunk growth. Not all copper compounds are approved for use in organic production; be sure to check individual products.
 
C. COPPER SULFATE# Label rates 24 When dry
  RANGE OF ACTIVITY: Pests: narrow (trunk climbers); Natural enemies: few, if any
  PERSISTENCE: Pests: long; Natural enemies: none to short
  COMMENTS: Tree trunks can be banded with a slurry of basic copper sulfate with a small quantity of boiled linseed oil added as a sticker. Paint or spray it on the tree trunks in about a 4-inch-wide band. Not all copper compounds are approved for use in organic production; be sure to check individual products.
 
D. METALDEHYDE
  (Deadline) Pellet 20–40 lb/acre 12 0
  RANGE OF ACTIVITY: Pests: narrow (snails); Natural enemies: beneficial snails
  PERSISTENCE: Pests: short; Natural enemies: short
  COMMENTS: For use on all varieties. Use higher rate for heavy infestation.
 
E. IRON PHOSPHATE
  (Sluggo) G Label rates 0 0
  RANGE OF ACTIVITY: Pests: narrow (snails); Natural enemies: beneficial snails
  PERSISTENCE: Pests: intermediate; Natural enemies: intermediate
  COMMENTS: Apply using standard fertilizer granular spreader. If ground is dry, wet it before applying bait. Reapply as bait is consumed or at least every 2 weeks. Check with CCOF to determine if this product is acceptable for use on organically certified produce.
 
FOLIAR APPLICATION
 
A. PHOSMET
  (Imidan) 70W 1-3 lb/acre (TC) 3 days 7
  RANGE OF ACTIVITY: Pests: broad (many insects, mites); Natural enemies: most
  PERSISTENCE: Pests: intermediate; Natural enemies: short
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Use allowed under a 24(c) registration. Do not make more than two applications per season or use in combination with oils.
 
** TC - Thorough coverage uses 750–2,000 gal water or more/acre, depending on tree size.
Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
# Acceptable for use on organically grown produce.
1 Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode-of-action Group numbers ("un"=unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.
NA Not applicable.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441

Insects, Mites, and Snails

  • E. E. Grafton-Cardwell, Entomology, UC Riverside and Kearney Agricultural Center, Parlier
  • J. G. Morse, Entomology, UC Riverside
  • N. V. O'Connell, UC Cooperative Extension, Tulare County
  • P. A. Phillips (emeritus), UC IPM Program, UC Cooperative Extension, Ventura County
  • C. E. Kallsen, UC Cooperative Extension, Kern County
  • D. R. Haviland, UC Cooperative Extension, Kern County
Acknowledgments for contributions to Insect, Mites, and Snails:
  • J. Barcinas, E.S.I., Corona, CA
  • R. Dunn, Badger Farming Co., Exeter, CA
  • J. Gorden, Pest Management Associates, Exeter, CA
  • H. Griffiths, E.S.I., Corona, CA
  • D. Machlitt, Consulting Entomology Services, Moorpark, CA
  • C. Musgrove, retired entomologist, Riverside, CA
  • K. Olsen, S & J Ranch, Pinedale, CA
  • T. Roberts, E.S.I., Corona, CA
  • T. Shea, UC Cooperative Extension, Riverside County
  • J. Stewart, Pest Management Associates, Exeter, CA
  • P. Washburn, Washburn & Sons Citrus Pest Control, Riverside, CA

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