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How to Manage Pests

UC Pest Management Guidelines


Gray garden slug crawling on ripe strawberry.

Strawberry

Slugs

Scientific Names:
Garden slug: Arion hortensis
Little gray slug: Deroceras reticulatum and other species

(Reviewed 6/08, updated 6/08)

In this Guideline:


DESCRIPTION OF THE PESTS

Slugs have no shell, are slimy and have bodies that are flexible in shape. They move by gliding along on a muscular "foot." This muscle constantly secretes mucus, which later dries to form the silvery slime trail that signals the presence of these pests. Slugs can be found on the plant at night and in the early morning, and under the plastic or other mulch during the day. They are sensitive to dryness, and will seek out moisture, making the humid environment under the mulch of strawberries attractive to them.

The garden slug is larger than the little gray slug. It measures about 1 to 1.5 inch in length and is gray to dark brown in color. Living for about one year, the garden slug is sexually mature in about 3 weeks. This slug is sensitive to cold and many will not survive a cold winter.

The little gray slug measures about 0.5-0.75 inches (12-19 mm) in length and has a mottled gray color. It takes from 3 to 4 months for the little gray slug to reach maturity. This slug is less sensitive to cold than the garden slug and is better able to survive mild winters in high numbers.

Peak egg-laying for both slugs occurs from late September through early November. Most eggs deposited before late October hatch during fall; those deposited in November hatch from late February through spring.

DAMAGE

Slugs feed on ripe fruit and produce rough holes that render the fruit unmarketable. These holes may be invaded by a number of secondary pests such as sowbugs, earwigs, and small beetles. Slugs also feed on the leaves of strawberries, and the effects of the rasping feeding are ragged holes in the leaves.

MANAGEMENT

Cleaning up debris in fields to make them less hospitable to slugs can help prevent large numbers from developing. If damaging populations of slugs are present, baits can be applied in nonorganic fields.

Cultural Control
The elimination of hiding places such as rocks, weeds, logs and boards will assist in reducing the numbers of slugs, because of the removal of habitat. Furthermore, growers can seek to plant away from areas with lots of debris, such as leaves and ground covers.

Organically Acceptable Methods
Cultural controls and the use of Sluggo bait are acceptable for use on organically certified strawberries.

Treatment Decisions
Apply baits during fall and spring when slugs are most mobile on the ground surface in search of food and mates. Adverse weather conditions keep the slugs, especially the juveniles, inactive and they do not consume enough bait. The efficacy of metaldehyde baits may also be reduced by cool, wet weather because slugs produce less mucus during these periods.

Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (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. METALDEHYDE
  (Deadline) 4% bait 10–20 lb/acre 12 0
  COMMENTS: Use higher rate for heavy infestation. This bait has minimal impact on other organisms in the field. Avoid contacting the fruit with bait.
 
B. IRON PHOSPHATE#
  (Sluggo) G 24–44 lb 0 0
  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.
 
+ 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.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Strawberry
UC ANR Publication 3468
Insects and Mites
F. G. Zalom, Entomology, UC Davis
M. P. Bolda, UC Cooperative Extension Santa Cruz County
P. A. Phillips, UC IPM Program/UC Cooperative Extension Ventura County
Acknowledgment for contributions to the Insects and Mites:
N. C. Toscano, Entomology, UC Riverside

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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