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How to Manage Pests

UC Pest Management Guidelines


Removing cardboard wrap from around a young avocado trunk to reveal brown garden snails, Helix aspersa, hiding underneath.

Avocado

Brown Garden Snail

Scientific name: Cantareus aspersus (=Helix aspersa)

(Reviewed 1/07, updated 8/08)

In this Guideline:


DESCRIPTION OF THE PEST

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 Its body and a pair of antennalike sensory appendages can be withdrawn into its shell.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. In southern California, particularly along the coast, young snails are active throughout the year. Mature snails hibernate in topsoil during cold weather.

DAMAGE

Extensive chewing of blossoms, leaves, and shoots stunts the growth of young trees and trees that have been topworked. 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 chewing.

MANAGEMENT

Inspect young and topworked trees regularly for chewing 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 around trunks to retard snail populations and to suppress root rot and weeds. Frequent microsprinkling 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 southern California counties. Decollate introductions are not recommended in avocado. Establishment of significant decollate populations 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. Certain snail baits are available for spot applications. Molluscicides also kill predatory decollate snails. Pesticides are rarely warranted for mollusk control in avocado.

Common name Amount to use R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to the impact on natural enemies and honey bees and environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. METALDEHYDE G
20–40 lb/acre
12
0
  COMMENTS: Use the higher rate for heavy infestations.
 
B. COPPER BANDS#
Label rates
  COMMENTS: Place copper foil band around the tree trunk at a height of 1-2 feet above the ground. Overlap the copper foil on the tree trunk about 8 inches so it will slip and allow for trunk growth.
   
C. BORDEAUX MIXTURE#
  (10:10:100)
Label rates
see label
see label
  MODE OF ACTION: An inorganic insecticide.
  COMMENTS: A slurry containing tribasic copper sulfate can be sprayed on trunks to act as a barrier. Not all copper compounds are approved for use in organic production; be sure to check individual products. Be sure to follow label directions for products used. For information on making a Bordeaux mixture, see UC IPM Pest Note: Bordeaux Mixture, ANR Publication 7451.
   
D. IRON PHOSPHATE
  (Sluggo)
Label rates
0
0
  COMMENTS: Apply using standard fertilizer spreader. If ground is dry, wet it before applying bait. Reapply as bait is consumed or at least every 2 weeks. Check with your organic certifier to determine if this product is acceptable for use on organically certified produce.
   
+ 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 are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.
Not applicable.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Avocado
UC ANR Publication 3436
Invertebrates
P. A. Phillips, UC IPM Program, UC Cooperative Extension, Ventura County
B. A. Faber, UC Cooperative Extension, Santa Barbara/Ventura counties
J. G. Morse, Entomology, UC Riverside
M. S. Hoddle, Entomology, UC Riverside
Acknowledgment for contributions to Invertebrates:
M. Blua, Entomology, UC Riverside
P. Oevering, UC Cooperative Extension, Ventura County
D. Machlitt, Consulting Entomology Services, Moorpark, CA
T. Roberts, Integrated Consulting Entomology, Ventura, CA
B. B. Westerdahl, Nematology, UC Davis

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