Northwest berry Foundation

Management Detail

Slugs

in Blueberries

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

Description:

Reason for Concern:
1) Slugs are not a major blueberry pest. However, given the right environmental and field conditions they can be numerous enough to cause economic damage.
2) 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.
3) Can be a contaminant in the harvested fruit. They are most likely to be a problem in cool, wet summers.

Identification/Symptoms:
Slugs vary in size depending upon the species, from 1/4 to 7 inches long. They secrete a characteristic slime trail as they move that is silvery upon drying. The color of slugs varies with species, ranging from dark black-brown to orange. The gray garden slug is a mottled gray to black, usually less than 1 inch long. The European black slug has 2 color forms, black or red. The red form is common in the west. Eggs look like round gelatinous spheres filled with a watery substance and are 1/8 to 1/4-inch in diameter. Baby slugs resemble adults but are smaller and may not be as fully colored.

Lifecycle:
All slugs lay eggs. Each species requires a different length of time for the development of its eggs and the maturing of its young. Most species overwinter as adults or nearly mature young. In the spring, eggs (up to 100) are laid in moist areas and the young reach maturity by fall. During periods of particularly warm and wet climatic conditions, the rate at which the slugs develop may allow for eggs to be laid in mid-summer, making a second generation possible. Mating usually takes place from August until mid-October and eggs can be laid from 30 to 40 days after a successful mating. Eggs are generally laid on or near the soil surface, but are usually deposited in places of concealment. The minimum temperature for egg development is between 32 to 42 degrees F. At the minimum temperature, as long as 100 days may be required for eggs to develop. At higher temperatures, development is usually completed in 10 days to 3 weeks. Newly hatched slugs can crawl and feed. Slugs are mainly nocturnal and remain motionless and concealed until nightfall provides suitable conditions for activity. The rate of growth of immature slugs depends on type and amount of food available. Dry conditions usually result in weight loss, which is regained rapidly when moist conditions return.

Links:

Scouting:

  • Look for slime trails they leave behind.
  • They can also be a contaminant in the harvested fruit.
  • When branches, heavy with fruit, bend down and make contact with the ground or vegetation between the plant rows slugs can readily climb onto the plants and into the fruit clusters.
  • They are most likely to be a problem in cool, wet summers.
  • 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:

  • Baiting after harvest in the fall helps reduce next year’s population by controlling the egg-laying adult slugs.
  • 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.
  • Because 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.

 

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

images


photo by R. Berry


photo by T. Peerbolt


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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Northwest Berry Foundation

Northwest Berry Foundation

© 2016

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