Northwest berry Foundation

Management Detail


in Blackberries

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Latin name: Limax spp., Arion spp., Deroceras spp.


Reason for Concern:
1) Given environment and field conditions, slugs can be numerous and cause economic damage.
2) Climb canes and move onto berries, on which they become contaminants.
3) Most likely to be a problem in cool, wet summers.
4) Migrate into and under crates taken to the field before harvest.

A slug is a snail without a shell: a soft slimy body with extensible eyestalks. They vary in size depending upon species and measure from 1/4 to 7” long. They secrete a characteristic slime (mucus) trail that is silvery upon drying and is a common diagnostic used to identify presence. Color varies with species, from dark black-brown to orange. The most common slugs found in the northwest are the Gray Garden Slug (generally a mottled gray to black in color usually less than 1” long), and the European Black Slug (either black or red); the red form is common in western regions. The eggs are round gelatinous spheres filled with a watery substance, from 1/8” to ¼” in diameter, usually colorless, often reflecting the color of their surroundings, but may become cloudy just before hatching. Baby slugs resemble adults but are smaller and may not be as fully colored.

All slugs lay eggs, but eggs develop and young mature over different time lengths. One slug may lay up to 100, but average 20 to 30, eggs in spring and early summer. Most species overwinter as adults or nearly mature young. In spring, eggs are laid in moist areas and new slugs reach maturity by fall. During warm and wet conditions, the rate at which the slugs develop may allow for eggs to be laid in mid-summer, making possible a second generation. Slugs mate from August to mid-October and lay eggs 30 to 40 days later. Minimum temperature for egg development is 32 to 42 degrees F with up to 100 days hatch. At hatch slugs are active and begin to feed if temperature and humidity are right. Slugs are mainly nocturnal remaining motionless and concealed until nightfall.



  • Train workers on harvesting machines to remove them. Keep a container for the workers to put insect contaminants. This can be used monitor their numbers.
  • Look for slime trails.
  • Populations can be monitored by placing small mounds of slug bait (or bait stations) near potential slug habitat and checking periodically for activity.

Cultural Controls:

  • Slugs migrate into and under crates taken to the field before harvest, so keep crates and pallets away from damp soil and grass.
  • Maintain vegetation free row middles and in rows.


For information about chemical controls, check with our Pesticide Guide.


photo by R. Berry

photo by T. Peerbolt

photo by T. Peerbolt

photo by T. Peerbolt

photo by T. Peerbolt

photo by T. Peerbolt

Slug with egg - photo by T. Peerbolt


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