Root Weevils in Ontario Strawberry Fields

Introduction

Root weevils cause sporadic but substantial yield loss losses in strawberries. A research project was initiated by Agriculture and Agri-Food Canada in 2004 to identify species of weevils active in strawberry fields and to investigate monitoring tools, treatment thresholds and integrated control strategies. This project involves collaborators and projects in eight provinces. Here we report on root weevil monitoring in 2004 in Ontario.

Black vine weevil adult

Weevil larva

Strawberry root weevil larvae on roots

Strawberry field damaged by root weevil feeding

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Monitoring studies:

In 2004, four fields in southern Ontario were intensively monitored each week for root weevils using various traps and visual assessment. We also collected samples from seven additional sites where root weevils were reported.

Three types of traps were used to monitor root weevil activity in the field. Visual assessments were made by inspecting 0.25 m2 of the straw mulch and soil surface along the row near each set of traps.

Pitfall traps and barrier pitfall traps were most effective at trapping black vine weevils. Board traps were not effective. Visual assessments were tedious and inefficient.

Pitfall trap used for monitoring root weevils

Barrier pitfall trap used for monitoring root weevils

Grooved board trap.
This trap is buried beneath the straw with the grooved surface contacting the soil

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Leaf notching provided good indication of black vine weevil adult activity, but may not be a good indicator for strawberry root weevil.

Leaf notching caused by adult black vine weevil

Thirteen different species of root weevils were identified from Ontario sites. Black vine weevil (BVW) (Otiorhynchus sulcatus) was most commonly associated with damage to strawberry plants. BVW was the dominant species collected at 8 sites. Strawberry root weevil (O. ovatus) predominated at 1 site while the brown punctate weevil (O. raucus), collected for the first time on strawberry, predominated 1 site.

Adults were most active in late July, throughout August, and into September.

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Sporadic adult activity in May and early June may be the remnants of an overwintering adult population.

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Seasonal activity of adult black vine weevils in representative fields

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Beneficial nematodes to control root weevils: A commercial formulation of beneficial nematodes, Nemasys H (Heterorhabditis megadis) was applied to a 13 row swath in an infested field. The product was applied at approx. 2 billion nematodes/acre using hand-held hose, fed from a 500 gallon tank of water, on June 3, when root weevil larvae were in the late instar stage. Nematode-infected root weevil larvae were subsequently detected throughout the treated area, but not in adjacent areas of the field.

Reddish pink larvae are infected with beneficial nematodes

Nematodes exiting deceased root weevil larva

Barrier fences: Root weevil adults are flightless; adults move to new fields on foot. Barrier traps may be a useful tool for preventing infestation of new fields. A simple 18" plastic barrier fence supported with 2"x2" stakes was erected between an infested field and non-infested field. Large numbers of weevils were trapped in the pitfall traps at each end of the barrier, indicating that at least some weevils tended to move along the barrier rather than climb over it.

Barrier fence to prevent weevil migration

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