Black vine weevil (Otiorhynchus sulcatus)
Pest description and crop damage Adult weevils are black, 0.4 inch long, and appear May through July. Larvae are C-shaped, legless, and white with tan heads, up to 0.5 inch in size. Adult weevils cause a characteristic notching in the leaves of host plants. This feeding damage is relatively minor. The real damage is done by the larvae, which feed through the winter and spring on the root systems of host plants. Infested plants are stunted, grow poorly, and may die.
Biology and life history Weevils overwinter as larvae in the soil. Feeding may occur throughout mild winters. In April to June, larvae pupate, and adult emergence occurs. Adults are night feeders that remain in the soil or in debris at the base of the plant during the day, then climb up to feed on leaves. Adult weevils cannot fly, but walk or are carried from one location to another. Also, all adults are females capable of laying eggs. Adults are slow moving and should not be confused with swifter predacious ground beetles. Eggs are laid in clusters in or on the soil from June to September. The eggs hatch, and the larvae immediately wriggle through the soil to begin feeding. There is one generation per year.
Scouting and thresholds Observe leaves for first signs of notching in early summer (primroses are an inexpensive preferred host and can be used as an indicator plant for conifer field production. Confirm presence of adults by night inspection of foliage on warm, still evenings. Or, look for adults by day in debris at the base of the plant. Laying a small piece of cardboard at the base of the plant provides a refuge that you can check easily in the early morning. Commercial root weevil traps are available.
Management-biological control (larvae)
Natural enemies include:
- carabid (ground) beetles several species
- pathogenic nematodes (Heterorhabditis heliothidis, H. medidis, Steinernema carpocapsae, S. feltiae, S. kraussei, S. riobravis)-Adequate soil moisture and temperature are necessary for success.
- acephate (Orthene TR, Precise) at 0.024 lb ai/1,000 sq ft broadcast (0.6 oz). REI 24 hr.
- acetamiprid (Tristar 30SG) at 0.81 to 1.59 oz ai/100 gal. REI 12 hr.
- azadirachtin (Azahar, Azatin XL)-Some formulations are OMRI-listed for organic use.
- Beauveria bassiana (Botanigard, Mycotrol, Nautralis L)-Some formulations are OMRI-listed for organic use.
- bifenthrin (Talstar S) at 0.168 to 0.335 lb ai/1,000 sq ft. REI 12 hr. Restricted use pesticide.
- dinotefuran (Safari 20SG) at 0.1 to 0.2 lb ai/1,000 ft sq; 0.05 to 0.1 lb ai/100 gal. REI 12 hr.
- cyfluthrin/imidacloprid (Discus N/G) at 0.063 lb ai/100 gal foliar; 0.009 to 0.014 lb ai/1,000 ft soil. REI 12 hr.
- imidacloprid (Marathon) at 0.027 oz ai /100 gal foliar. REI 12 hr. Drench and irrigation permitted.
- Isaria fumosoroseus (PFR 97) at 4 to 8 fl oz per pot as soil treatment. REI 4 hr. Some formulations are OMRI-listed for organic use.
- permethrin (Permethrin 3.2 AG)-Restricted use pesticide.