Mint-Root weevil

Black vine weevil (Otiorhynchus sulcatus)
Strawberry root weevil (O. ovatus)

Pest description and crop damage Larvae are legless white grubs with tan heads. They overwinter 2 to 8 inches deep in the soil. Adults generally are black but may be brown or chocolate brown. Larvae feed on mint roots, and adults feed on foliage.

Scouting and thresholds Sweep fields for adults on a calm, warm night (above 70°F) beginning in late May, June. A few weevils (five or more) in the net after 10 sweeps at various sites within the field may need control. An infestation of from five to eight larvae per 1 sq ft soil sample the depth of the mint roots usually signals need for control. Sample for larvae in April/May.

Management-chemical control

  • acephate (Acephate 90WDG, Orthene) at 1 lb ai/A. PHI 14 days. REI 24 hr. Retreatment interval 7 days. Do not exceed 2 lb ai/A per season, nor make more than two applications per crop season. Grazing of animals on treated areas, and feeding of spent mint hay to animals are prohibited. For control of adult weevils. Apply late May through early June after adults emerge but before egg laying when weevils are feeding actively on foliage. Apply on warm, still evenings, usually between 10 pm and 2 am. Two applications 10 to 14 days apart may be necessary to reduce large infestations, particularly in central Oregon.
  • azadirachtin (Neemix 4.5 IGR) at 0.012 to 0.044 lb ai/A. PHI 0 days. REI 4 hr. Some formulations are OMRI-listed for organic use.
  • Beauveria bassiana (Mycotrol) Check each label for application rate. PHI 0 days. REI 4 hr. Most effective when used at first detection. Some formulations are OMRI-listed for organic use.