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Ministry of Agriculture, Food and Rural Affairs

Slugs

Slug egg  Slug Slug Slug feeding damage on fruit Typical slug damage on leaves Slug feeding damage on fruit Click to enlarge.

Beginner

Scientific Names
Deroceras (Agriolimax) species and Arion species

Identification

  • Soft-bodied, slimy
  • Tear-drop shaped and legless
  • Anywhere from 4 to 18 cm (1 2/3- 7 in.) in length
  • Dark grey, black, yellow-grey or brown
  • They produce small to moderate holes in fruit
  • A slime-glistening trail is left on fruit and leaves

Often Confused With
Bird damage to fruit

Period of Activity
Slugs have two populations: one that is active in the spring and the other in the fall. Damage to strawberry fruit is mainly caused by slugs which hatch from eggs laid the previous autumn. This population hatches just before harvest. Most species of slugs are active only at night, during overcast days or in the shade of a thick plant canopy.

Scouting Notes
Check weeds and legumes for leaf shredding caused by slugs. Check fruit and foliage for slugs when dew is present (early morning, late evening) or on rainy days. Slug injury is easy to recognize by the slimy trail left on the surface of the fruit.

Thresholds
None established. Damage is relative to the weather and microclimate in the field. Growers with a history of problems should take preventative measures.

Advanced

Scientific Names
Deroceras (Agriolimax) species and Arion species

Identification
Slugs are soft-bodied, slimy, tear-drop shaped, legless, worm-like molluscs ranging in colour and size. They can be anywhere from 4 to 18 cm (1 2/3- 7 in.) in length. They can be dark grey, black, yellow-grey or brown and may or may not have spots.

Slugs produce small to moderate holes in fruit. A slime-glistening trail is left on fruit and leaves.

Often Confused With
Bird damage to fruit (Both break the surface of the fruit and cause holes in the flesh. Bird damage is more irregular in shape and occurs on the side of the fruit exposed to the sun. Slugs are associated with slime trails.)

Biology
Each of the two populations have one generation per year, each with a 9- 12 month lifespan. Spring population slugs hatch from resting eggs in late summer, develop during fall and winter, overwinter as adults, and lay eggs in the late spring. Fall population slugs hatch in late spring from overwintered eggs which were laid in the late fall. These larvae develop over the summer and lay eggs in the fall. Both populations hatch in response to cooler temperatures and moisture and may be active at the same time.

Period of Activity
Slugs have two populations: one that is active in the spring and the other in the fall. Damage to strawberry fruit is mainly caused by slugs which hatch from eggs laid the previous autumn. This population hatches just before harvest. Most species of slugs are active only at night, during overcast days or in the shade of a thick plant canopy.

Scouting Notes
Check weeds and legumes for leaf shredding caused by slugs. Check fruit and foliage for slugs when dew is present (early morning, late evening) or on rainy days. Slug injury is easy to recognize by the slimy trail left on the surface of the fruit.

Thresholds
None established. Damage is relative to the weather and microclimate in the field. Growers with a history of problems should take preventative measures.

Management Notes

  • Slugs do the most injury during damp, rainy seasons, but they can cause damage in dry seasons when plantings are irrigated frequently. Irrigate early in the day to allow plants to dry rapidly by nightfall.
  • Slug populations can be reduced by good soil drainage. Rows should be kept narrow and weed-free to allow foliage to dry rapidly. Do not over fertilize with nitrogen.
  • Most insecticides are toxic to slugs. Therefore, in most situations, insecticide sprays applied to control tarnished plant bugs and strawberry clipper weevil will suppress slug populations. However, they will not control slugs if the plants have heavy foliage or if a thick straw mulch is present.
  • High risk factors for slugs include: wet years following mild winters, weedy, trashy areas, clovers or legumes nearby, thick straw mulch and vigorous leaf canopies.
  • Steps that can be taken to reduce slug populations include: lower-density plantings, removal of straw mulch, summer renovation of fields, delay of fall mulching and removal of trash and debris.