Northwest berry Foundation

Management Detail

Weevil, Rough Strawberry Root

in Blackberries

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Latin name: Otiorhynchus rugosostriatus

Description:

Reason for Concern:
1) One of many weevil species found in caneberries. It has been the predominant species and contributes to serious economic loss.
2) Emerges in early May and June; can be contaminants in machine-harvested fruit.
3) Larvae (grubs) feed on roots, weaken cane growth, devour roots and destroy bark and root cortexes.

Identification/Symptoms:
Larvae are white or pink, legless, "C" - shaped grubs. In the larval stage, size is the only characteristic that distinguishes one species from another. About 9 mm long when fully grown with distinct brown heads. Found in soil during most of winter and summer. Adults are flightless, hard-shelled beetles, oblong, oval in shape and slightly more than ¼” long (a size between black vine and strawberry root weevils). They have a broad snout, long, downward curved mouthparts and elbowed antennae. Body is blackish-brown and wing covers have numerous small pits and hairs. The collar just behind the head is heavily pitted. They feed at night and hide around plant crowns during the day. Presence of adult weevils can be detected by distinct notching patterns along leaf margins. Unlike other weevil species, rough strawberry root weevils tend to feed at the base of plants and in detritus.

Life Cycle:
Adults (nearly all females) appear after bloom, beginning in May and continuing through and after harvest. They climb canes at night to feed on foliage and lay their eggs around crowns about 1 month after emergence. Lay many of their eggs in late summer/early fall: many each day during adult phase (90-100 days). Eggs hatch in 2 to 3 weeks into young larvae that work their way into soil and feed on roots and crowns. In the larval stage, size is the only characteristic that distinguishes one species from another. Larvae grow slowly over summer, molting five to six times. By late fall, they have matured to about 5/8” long. They enter a prepupal stage in an earthen cell and pupate the following spring/summer. There is one generation per year.

Links:

Scouting:

  • In early-mid April, begin taking 10 beating tray samples from several sites in the field (monitoring technique developed by Washington State University, Whatcom County Raspberry IPM Manual), and record the number found. This is most effective at night or on cool cloudy days as this is when weevils will stay in the foliage.
  • In late May, begin examining foliage for weevil feeding signs (notching of the leaf margins). Rough Strawberry do not show as much leaf notching as other weevil species.
  • 1 or 2 weevils found for every 10 beating tray samples taken may warrant the consideration of a pre-harvest spray to target those weevils.

 
Cultural Controls:

None listed at present.

 

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

images


photo by K. Gray


Rough strawberry root weevil larva - photo by K. Gray


photo by K. Gray

 

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