Northwest berry Foundation

Management Detail

Weevil, Black Vine Root

in Blueberries

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Latin name: Otiorhynchus sulcatus

Description:

Reason for Concern:
1) Weevil larvae can feed on and girdle the roots, rootlets and basal crown area and are especially harmful to young plants.
2) Adults feed at night on leaves, notching the leaf edges.
3) Feeding damage results in stunted plants, poor yields, and possibly plant death.

Identification/Symptoms:
Larvae are legless, C-shaped, and white or pink with brown heads. Black Vine larvae are up to 1.3 cm long when fully grown. Strawberry Rough larvae are slightly smaller and Strawberry Root larvae are the smallest. Adults are flightless, hard-shelled beetles with coarse punctures on their wingless wing covers. They are oblong, have a broad snout, long, downward curved mouthparts and elbowed antennae. They feed at night and hide around the crowns of plants during the day. Strawberry Root Weevils are about 1/5 inch long, shiny black with thinly scattered yellowish short hairs (pubescence), and reddish-brown antennae and legs. Black Vine Weevils are about 1/3 inch long, black with patches of orange or yellow scales.

Lifecycle:
Root weevil larvae overwinter 2 to 8 inches deep in the soil, feeding on small roots that can quickly reduce the vigor of young plants. Adults (nearly all females) appear after bloom, continuing through and after harvest. The beetles do not fly but are strong walkers, able to climb into the canopy at night to feed on foliage. They lay their eggs around the crowns about 1 month after emergence (usually July or August). Eggs are deposited without fertilization on the soil of host plants. They lay several eggs each day and usually lay 200 eggs during their adult lifetime (90-100 days). Rough strawberry root weevil, unlike other weevil species, lay many of their eggs in late summer/early fall. Eggs will hatch in 2 to 3 weeks. The larvae work into the soil and feed on roots and crowns. Larvae grow slowly over the summer, molting 5 to 6 times. By late fall, they have matured and are about 5/8-inch long. They enter a prepupal stage in an earthen cell and pupate the following spring/summer. There is 1 generation per year. Because they are flightless, spread can be relatively slow; however, they are active walkers.

Links:

Scouting:

  • Detection can be found by using pitfall traps or temporary shelter (tile, cardboard, plywood, etc).
  • Greater attention should be given to younger plantings as weevils can girdle and kill young plants.
  • Start inspecting the soil in April for signs of damage from larvae. Watch for leaf notching, especially on sucker growth near the ground.
  • Adult weevils feed at night and usually return to the trash at the base of the plant in the day.
  • Weevils may stay in the foliage on cool, cloudy days especially if the foliage is dense.
  • To confirm weevil contribution to low vigor locations, dig up plant and look for evidence of grub population in roots. Note developmental stage to help time treatment.

 
Cultural Controls:

  • Tillage helps reduce weevil populations by crushing the soft-bodied larvae, but is not a standalone method.
  • Adjacent area management can aid in reducing in-field populations; adult weevils don’t fly.

 

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

images


photo by J. Troubridge


photo by K. Gray


Black vine weevil larvae in roots - W. MacDiarmid


Black vine weevil eggs - K. Gray


Various stages of black vine weevil from larva to pupa, to newly emerged adult with still soft body, to fully black adult - photo by T. Peerbolt

 

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