Black vine weevils, Otiorhynchus sulcatus, are primarily pests of species in the genera Taxus and Rhododendron. The weevils also target azaleas, mountain laurel and Euonymous. Adult black vine weevils feed on the leaf and needle margins, leaving distinct half-circular notches. Larvae appear similar to grubs you would find in your lawn except they are less “C” shaped and lack the thoracic legs. They feed in the spring on fine roots and in the fall will change to larger ones; this may result in a girdling of the stem right about the soil line. The adult black vine weevils are black with white flecks and grow to about 3/8 inches long. All adult black vine weevils are female. Damage caused by feeding will cause chlorosis, premature death and drop of leaves.
Black vine weevils overwinter in the soil as partially grown larvae, termed “pre-pupa”, they resume feeding in the early spring when the heaviest damage is caused. Larvae pupate in late May to early June. Adults will begin emerging in June or when the season reaches 600 growing degree days, and continue through July. Adult weevils feed at night and hide near the base of the plant during the day. Within 2 or 3 weeks of continuous feeding they will begin laying eggs, this is usually around late July. Larvae hatch in August, feed on roots beginning the whole cycle anew.
Distinctive damage inflicted by adult feeding is most visible from March through November. Although this damage will be from the previous season, it is a good indicator that you may want to take control measures or set up traps to confirm the presence of black vine weevils. The traps can be used to catch and dispose of adults before they can mature and lay eggs. If cultural measures don’t work to contain and eliminate the issue there are other methods such as nematode applications which are very effective at controlling black vine weevils. If you have concerns or questions about possible weevil issues on your property contact your arborist as soon as possible.