Brown Garden Snail

The brown garden snail (phylum Mollusca, family Helicidae) has a soft, slime-covered brown body. Its body and a pair of antennalike sensory appendages can be withdrawn into its shell. The hard spiraling shell grows up to about 1.25 inches in diameter. The shell is brown, tan, and yellow patterned in bands, flecks, and swirls.

Snails are hermaphroditic; they contain both male and female organs. After mating, snails drop eggs in a scattered group in a sheltered spot on topsoil. Mature snails lay eggs up to six times during a year, depending on climate and moisture.

Snails are most active during the night and early morning when surfaces are damp, such as after irrigation or rain. In southern California, particularly along the coast, young snails are active throughout the year. Mature snails hibernate in topsoil during cold weather.

Extensive damage due to rasping of blossoms, leaves, and shoots stunts the growth of young trees and trees that have been topworked. Damage is similar to that of a chewing insect. The brown garden snail can especially be a problem following wet winters and springs. Brown garden snail feeding is not a problem in mature groves. Thick, dry leaf mulch suppresses snail numbers and large trees tolerate any modest damage.

• Inspect young and topworked trees regularly for damage, especially during and after wet conditions. Be sure to distinguish the cause of damage. Caterpillars, earwigs, Fuller rose beetle, grasshoppers, and June beetles also chew tree foliage.
• Inspect surfaces for slimy or dry silvery trails characteristic of snails and slugs. Look for snails hidden under trunk wraps or other shelters near trunks.
• Modify cultural practices, encourage biological control, and exclude snails from canopies to provide good control.
• Control weeds in young groves and groves where tree canopies are sparse as low vegetation favors snails.
• Retain dropped leaves and apply coarse organic mulch near trunks to retard snail numbers and to suppress root rot and weeds. Frequent microsprinkler irrigation encourages snail problems.
• Increase the interval between irrigations to the extent compatible with good tree growth. Trim branches that touch soil to restrict snail access to canopies and expose the soil surface to drying.

Birds and other small vertebrates, parasitic flies, and several types of predatory beetles commonly prey on snails. The predatory decollate snail (Rumina decollata, family Subulinidae) is widely distributed in southern California. Decollate snail is commercially available and legal for introduction only in certain San Joaquin Valley and southern California counties (Fresno, Imperial, Kern, Los Angeles, Madera, Orange, Riverside, Santa Barbara, San Bernardino, San Diego, Ventura, and Tulare counties). Decollate introductions are not recommended in avocado. Establishment of significant decollate numbers usually requires several years after introduction, and brown garden snail primarily is a pest when avocado trees are young.

Snails and slugs are repelled by copper. Commercially available bands of copper foil wrapped around trunks exclude snails. Another alternative is to add Bordeaux mixture to whitewash and paint 1 to 2 inch strip around the trunks of trees. Certain snail baits are available for spot applications. Molluscicides also kill predatory decollate snails. Pesticides are rarely warranted for mollusk control in avocado.