WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Slugs

(Limax spp., Arion spp., Deroceras spp.)

Insects & Invertebrates

 

Slug

 

Symptoms

Slugs can climb up the blueberry plant and feed on foliage and berries; their feeding, and the slime trails they leave behind, can reduce fruit quality. They can also be a contaminant in the harvested fruit. They are most likely to be a problem in cool, wet summers, and when branches heavy with fruit bend down and make contact with the ground or vegetation between the plant rows.

 

Identification

Slugs are soft-bodied mollusks without a shell. They can range in length from ¼ inch to 10 inches long. They range in color from yellow to green to brown to black; some may have spotting or colored patterns. They have eyestalks that look like antennae. Slug eggs are small and semi-transparent.

Slug on leaf

Life History

Slugs can reproduce at any time of year. Each slug has both male and female reproductive parts. During mating, two slugs cross-fertilize to reproduce. Three to 40 eggs are laid at a time and up to 400 eggs can be laid by one slug each year. Eggs are laid in soil cracks. Eggs will hatch in a few weeks when late spring and summer weather is cool and moist. Newly hatched slugs must travel through the soil and feed on roots. After only three months, offspring can reproduce.

 

Monitoring

Look for slime trails starting in March.  Populations can be monitored by placing small mounds of slug bait (or bait stations) near potential slug habitat and checking periodically for activity.

 

Thresholds and Management

Threshold varies according to end product usage and processor. Talk to your buyer for their threshold.

Trellising the blueberry plants keeps branches heavy with fruit off the ground, which can reduce the number of slugs gaining access to the plant. Vegetation management (mowing or complete elimination) in the plant row and between the berry rows can reduce slug habitat. Slugs migrate into and under crates taken to the field before harvest; keeping crates and pallets away from damp soil and grass helps reduce the chance of contaminated fruit. Geese have been used with some success in small, organic blueberry fields.

Slug baits are registered for use in blueberries. The most widely used, and the most effective, are baits with methaldehyde. Baits containing iron phosphate are also available and have the added benefit of being approved for organic production; however, their efficacy is questionable. Baits can be applied broadcast or in a band, but must not come in contact with the fruit. Baiting prior to harvest is common if slugs are known to be present. Baiting after harvest in the fall helps reduce next year’s population by controlling the egg-laying adult slugs.

 

Resources

WSU Extension Bulletin 0968: Slug Control
http://cru.cahe.wsu.edu/CEPublications/eb0968/eb0968.html

Colorado State University, Slugs
http://www.ext.colostate.edu/Pubs/insect/05515.html

WSU Whatcom County Extension, Top 10 Most Un-Wanted Pests: Slugs
http://lakewhatcom.wsu.edu/gardenkit/UnWantedPests/Slug.htm

 

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WSU Whatcom County Extension • 1000 N. Forest St., Bellingham, WA 98225 • (360) 778-5800 • whatcom@wsu.edu