Northwest berry Foundation

Management Detail

Lecanium Scale

in Blueberries

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Latin name: Lecanium spp.

Description:

Reason for Concern:
1) Scales suck sap from the plants reducing plant vigor and terminal growth.
2) Scales secrete honeydew, which promotes the growth of a black sooty mould, makes picking unpleasant and may make fruit unsuitable for fresh market.
3) Feeding by the immature crawlers causes stunted and distorted growth, witches’ broom, and reduced fruit yield and quality.

Identification/Symptoms:
Small (up to 5 mm in diameter), yellowish-brown, helmet-shaped shells cover and protect scale eggs during dormancy. Eggs hatch into "crawlers" in spring and summer. The crawlers are about .5 mm long, flat and yellowish, with legs, eyes and antennae. Leaves may become sticky and discolored with heavy feeding. Mature females are yellowish brown turning later to dark brown covered with powdery or cotton-like material. They are oval and shell-like. Full-grown females are 3 to 5 mm long. The scales of the males are composed of delicate, almost transparent wax, with well-marked ridges.

Lifecycle:
Overwintering forms complete development by late spring or early summer. White eggs (1,000-plus) are laid under the bodies of the females during late May or June. The egg stage lasts 2 to 4 weeks. The eggs become pinkish and hatch in late June or July. After egg laying, the female dries into a hard shell on the surface and shrinks away from the eggs inside the shell, The young emerge as “crawlers” and move to the underside of leaves, feeding for 4 to 6 weeks before returning to the stems and twigs to overwinter. While feeding, crawlers secrete a brownish scale cover, becoming spindle or shell-shaped. The female has 3 instars and the male has 4. Pupation lasts about 1 month. The scales mate in early spring and the females continue to feed until early fall. The males die after mating.

Links:

Scouting:

  • During the dormant season, before pruning, (December) inspect plants and mark areas where many scales are seen. 4 locations, 5 plants, 10 tips.
  • Start to check for egg hatch and crawler migration prior to bud break. The crawler stage is most susceptible to control and can be monitored using double-sided sticky tape placed around branches.
  • If numerous enough, feeding by the immature crawlers can cause stunted and distorted growth and witches’ broom.

 
Cultural Controls:

 

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

images


photo by K. Gray


photo by K. Gray


photo by T. Peerbolt


photo by T. Peerbolt

 


photo by T. Peerbolt

 

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