Incidence and Management of Root Weevils in Ontario Strawberry Fields

Root weevils are significant pests of many crops, including strawberry. While adults feed on foliage, often leaving characteristic notches, economic injury is due to larval feeding on roots. In Ontario, the profitable life-span of heavily infested strawberry fields may decline from 3-4 years to two or fewer years. As part of a national, multi-year project to develop reduced risk pest management strategies for root weevils in Canadian berry crops, work was undertaken in selected Ontario strawberry fields to identify root weevils active in those fields and to evaluate potential of components of an integrated management program.

Identification

Twelve different species of root weevils were collected from Ontario sites in 2004-2006. Black vine weevil (BVW), Otiorhynchus sulcatus, is the most widespread and destructive weevil in Ontario. The smaller strawberry root weevil, O. ovatus, and a third species O. raucus occasionally cause significant damage.

Exclusion Barriers

Barriers to prevent weevil migration to new fields were evaluated in 2005. "Vernon Barriers" were built of 3 m lengths of purpose designed extruded black plastic. "Sheet Barriers" were made by supporting 30 cm wide sheets of plastic with 2x2 stakes, and with 1 edge buried 5-10 cm deep in soil. Collection pails were set at the ends of each barrier and numbers of adult root weevils captured were recorded.

Many more black vine weevils were collected moving around "Sheet Barriers" than "Vernon Barriers" . Perhaps the Vernon barriers were less effective because they tended to warp and lift from the soil due to solar heating. Details on constructing sheet barriers were published in the Ontario Berry Grower,
May 2006. Some growers have subsequently installed modified sheet barriers, intercepting as many as 600 adults/m barrier at 1 location.

Foliar Insecticides:

Effectiveness of post harvest application foliar insecticides was determined in 2008. Relative effectiveness was measured by sweep net captures of adult weevils. Sweeping confirmed that indicated that weevil adults are active at night, only after it is fully dark. In this preliminary evaluation, several insecticides were identified as potentially suitable for minor use registration in future.

Recommendations:

BVW is the most important root weevil attacking Ontario strawberries. Management requires an integrated program with emphasis on prevention. Elements of an effective strategy will include:

• tolerant cultivar selection and plant management for optimum root growth.
  
• rotation and isolation of new plantings from infested patches.
  
• exclusion barriers for new plantings.
  
• control by properly timed application of entomopathogenic nematodes or insecticides.
  
• timely destruction of infested patches to minimize weevil adult emigration.
  

Learm more:

• Root Weevils in Ontario Strawberry Fields (Hort Matters, vol #5, issue #6, Apr 28/05)
  
• Exclusion Barriers for Management of Black Vine Weevil in First Year Strawberries (Ontario Berry Grower April 2006)

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