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Ministry of Agriculture, Food and Rural Affairs

Strawberry Clipper Weevil

Strawberry clipper weevil adult on bloom Clipped bud from strawberry clipper weevils Close up of adult strawberry clipper weevil Monitoring for strawberry clipper weevils Older damage from strawberry clipper weevil: dried up bud Click to enlarge.

Beginner

Scientific Name
Anthonomus signatus Say

Identification

  • Adults are 2- 3 mm (1/12- 1/8 in.) long, reddish-brown with a long snout
  • Larvae and eggs develop inside strawberry buds and are rarely seen
  • Damage is caused by adult feeding and egg laying
  • Adults initially feed on pollen in strawberry buds and bloom, leaving round holes on buds and bloom as they do so
  • When eggs are laid, the female weevil cuts the stem below the bud, which causes it to dry out and drop off

Sometimes Confused With
Strawberry root weevil

Period of Activity
Adults become active in early spring, especially after a few warm nights.  Damage occurs until all flower buds are open.

Scouting Notes
Begin to monitor for clipper injury when strawberry buds emerge from the crown.  Check older fields for first signs of damage.  Check plants at the edge of the field near woods, bush and other overwintering sites.  Examine buds and unopened blossom clusters for clipped buds.  Sometimes the buds will remain partially attached, sometimes they will drop off the plant.  Freshly clipped buds will be green and only partially shrivelled.  As time passes these buds become quite dry and brittle.  Assess damage by counting clipped buds in 0.2 m2 (2 ft2) sections of the row.  Continue twice weekly until petal fall.

Thresholds
13 clipped buds per 0.2 m2 (2 ft2).

Advanced

Scientific Name
Anthonomus signatus Say

The strawberry clipper weevil (SCW) is one of two major insect pests that frequently causes economic losses in strawberry plantings.  It is believed to be native to North America.  Alternate hosts are blueberries, wild strawberry, and wild and cultivated brambles.

Identification
Adult: The strawberry clipper weevil is a small, reddish-brown weevil, 2– 3 mm (1/12- 1/8 in.) long with a long snout.  They can be found on blooms and in blossom clusters.

Larvae:  Eggs are laid in the strawberry blossom bud, where larvae develop.  These stages can be seen by dissecting dried-up buds.  Larvae are white, with no legs.

Damage:  Damage is caused by adult feeding and egg laying.  Adults initially feed on pollen in strawberry buds and bloom, leaving round holes on buds and bloom as they do so.  The female weevil lays an egg in a bud, and then cuts the stem below the bud, which causes it to dry out and drop off.

Often Confused With
Strawberry root weevil

Biology
In Ontario, there is one generation of the SCW per year.  The SCW overwinters as an adult in protected areas such as fence lines, hedgerows and under mulch. The SCW migrates into the strawberry field from its overwintering site. After mating, the female cuts a hole in the flower bud and lays one egg inside.  She then partially cuts off the blossom stalk a few centimetres (1/2 in.) below the bud.  This is where the common name the “Clipper Weevil” comes from.  The damaged bud will not open; it wilts, turns brown and dries up, providing a place for the egg and larva to develop.  Once the egg hatches the larvae develop inside the bud for approximately four weeks.  The larvae pupate inside the bud with adults emerging in mid-summer.  After emerging, adults feed on pollen from flowers and weeds until the fall when they seek out overwintering sites.  A resident population (one that becomes established inside the strawberry field) may develop in plantings older than three years.

Period of Activity
Overwintering adults become active in early spring, after several warm nights (16°C or 60°F) when strawberry buds extend from the crown.  Damage occurs until all flower buds are opened.

Scouting Notes
Begin to monitor for clipper injury when strawberry buds emerge from the crown.  Check older fields and sheltered areas for first signs of damage.  Check plants at the edge of the field near woods, brush and other overwintering sites.  Expect more damage in older fields, and near alternate hosts (i.e. raspberries). 

The standard way to monitor for SCW is with a 30 cm by 60 cm (1 ft. by 2 ft.) wooden frame.  Place the frame on a row and count all the clipped buds within the frame.  Check for clipped buds in a  total of 5 locations in the perimeter of the field.

Re-examine fields for newly clipped buds 5- 7 days after the date of the first insecticide application.  When reassessing the need for further insecticides, it is important to only count newly clipped buds.  Newly clipped buds will still be green, with only a little browning.  As time passes these buds become quite dry and brittle.  Monitor fields continuously for clipped buds every 3 days until the end of bloom, to assess the need for additional controls.

Thresholds
13 clipped buds per 0.2 m2 (2 ft2).

Management Notes

  • Apply an insecticide when the threshold is reached.  Border sprays of the ten first rows may provide adequate control in newer plantings.
  • In most situations, only one corrective spray is required.  Fields with severe SCW pressure may require a second spray, if the action threshold is reached 7 days after the application of the first insecticide.  Late SCW damage is often prevented when tarnished plant bug sprays are applied. 
  • Renovation should take place promptly after harvest.
  • Good weed control, especially the elimination of broadleaf weeds can reduce the survival of newly emerging SCW adults.
  • In the final fruiting year, plough down the field immediately after the last picking.  Follow this by summer fallowing and crop rotation, especially if you are replanting strawberries back into the same field.
  • Older fields tend to have more damage, so reduce pressure from clipper weevil by fruiting fields for two years or less.