Northwest berry Foundation

Management Detail

Weevil, Obscure Root

in Raspberries

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Latin name: Sciopithes obscurus

Description:

Reason for Concern:
1) Occur sporadically on berry crops.
2) Feed on foliage and can contaminate machine-harvested fruit.
3) Larvae (grubs) feed on the roots and weaken cane growth.

Identification/Symptoms:
All weevil species are similar in habit and appearance. In larval stage, size is the only characteristic that distinguishes one species from another. Larvae are white, legless, "C" - shaped grubs that feed on roots during most of summer and winter. Obscure weevils are mid-sized. Adults are flightless, hard-shelled, and have long, downward curved mouthparts and elbowed antennae. The obscure weevil is gray or brown with wavy brown lines across its back near the rear. It is about 5 to 7 mm long (1/4”).

Life Cycle:
Although they can emerge as early as May, obscure root weevil adults generally emerge beginning in August and are more numerous from August to October. Their behavior varies from other root weevils. The adult sometimes remains in foliage rather than climbing down the plant trunk to hide during the day. Obscure root weevil lays its eggs inside a folded edge of the leaf. As larvae emerge from the eggs, they burrow into soil to feed on roots. Females can lay 8 eggs/ day, roughly equivalent to a black vine weevil.

Links:

Scouting:

  • Unlike the other weevil species, Obscure root weevils spend most of their time in the foliage.
  • 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).
  • 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


Obscure root weevil damage - photo by R. Rosetta


Obscure root weevil eggs - photo by K. Gray


photo by J. Boyd


Obscure root weevil damage - photo by K. Gray


Leaf knotching by obscure root weevil - photo by B. Leung

 

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