Root Weevils In Strawberries: Recognize Them, Take Action

Root weevils can be a serious pest on strawberries. Damage can be extensive; a pocket of of damage in a corner of the field can expand and cause devastating losses the following year. Recognizing root weevils and their damage is the first step in preventing this problem. Unfortunately, control is difficult and there are few pesticide options.

The following photos can help you identify root weevils and their damage in the field. There are many good internet sources that provide details on life cycle and biology of these pests.See also Massachusetts Berry Notes, July 18, 2002 for a good article on root weevils and their control in strawberries.

Important facts that affect control

• Root weevil larvae feed on plant roots and crowns. Like most soil born insect pests, there are no labeled insecticides for control of larvae, and very few even being investigated.
  
• There are several species of root weevils, including the black vine weevil and the strawberry root weevil. They have similar life cycles and habits.
  
• Root weevils have a wide host range: Japanese yew; hemlock; white cedar; pine; spruce; Euonymus; Rhododendron; grapes and berries. They generally move onto a field from the edges.
  
• Root weevils can't fly. They walk from crop to crop. Expect them to travel short distances when food is available, but longer distances (several hundred feet) if they need to search for new food sources. Barriers and inhospitable conditions will slow migration to new fields.
  
• Root weevil adults hide in strawberry crowns and plant debris during the day, and feed mostly at night.
  
• Adults feed on strawberry foliage. The notches and semi-circles cut out of the leaf edge is characteristic. The injury alone is not serious, but it indicates a potential problem with the larvae next year.

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Control of root weevils

• To suppress root weevils, apply an insecticide labelled for root weevil adults in strawberries. (most azinphosmethyl labels list this pest) . Spray after strawberry renovation, at night, when adults are most active. Renovating the field first will help to expose the adults Adult weevils are hard to kill. They are secretive. They emerge and are active over extended periods of time. Their body design does not lend itself to control with contact insecticides.
  
• Strawberry renovation practices should include rototilling. Where weevils are a problem, do not narrow the rows with gramoxone, because the plant debris and undisturbed soil will favour weevil activity.
  
• Never plant new fields adjacent to older plantings.
  
• Disc infested fields under as soon as possible after harvest, but leave a trap row or two of the old planting at the edge of the planting to prevent mass exodus from the field.

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Unconventional attempts to control root weevils:

• Consider barriers or trap crops that will prevent weevils from moving to the new fields. We think that the plastic lined trenches used for Colorado potato beetle might work.
  
• Researchers are focussing on use of beneficial nematodes to control root weevil larvae. The beneficial nematodes are available commercially. They must be applied with great care and at specific timings in order to survive the application process and reach the weevil larvae, which they infect.
  
• A grooved board has been developed to capture and collect adult weevils. Using traps like this could be used to monitor migration of weevil larvae to new fields.

  If your fields are plagued by root weevil, and you would like to investigate these alternative methods, please call Pam Fisher or Hannah Fraser. We would like to work with you.

Recognizing the stages of root weevils:

Figure 1: Adult root weevil.
There are several species, sizes and colour variations.
All have the same shape, snout, and hard shell.

Figure 2: Root weevil larvae: these larvae, pinkish white in colour,
can be found in spring on strawberry plant roots. They are small, only 1/2- 1 cm in length.

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Figure 3: Larvae are legless, with a brown head capsule.

Figure 4: Damage to strawberry plants.
Dead plants are clustered together, with less severely infested plants adjacent to the dead ones.

Figure 5: Overview of field with root weevil damage.
The problem started at the field edge.

Figure 6: Leaf notching on strawberry leaves caused by adult weevil feeding.

Related Links

• Massachusetts Berry Notes, July 18, 2002
• OMAFRA Publication 360, Fruit Production Recommendations
• OMAFRA Berry Index Page
• Berry Bulletin Agriphone

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