Black Vine Weevil & Other Root Weevils

What are root weevils?

Black vine weevils (Otiorhynchus sulcatus) are one of numerous species of weevils (snout beetles) whose larvae feed on plant roots. Because larvae damage roots they are sometimes collectively called root weevils. Root damage can be so severe that plants, especially young or shallow-rooted ones, can be killed. Older larvae can also girdle (remove bark) stems as well. In fact, root weevils are among the most damaging of woody landscape plant pests worldwide.

Adult weevils feed on plant leaves resulting in characteristic notching (right). There is generally only one generation per year and control efforts should be directed at newly emerged adults, not larvae. When notching of new growth is first found in early summer you should begin your control program.

Common names and misspellings: strawberry weevil, obscure weevil, rootweevil, and blackvine weevil.

Least-toxic root weevil control

The critical time for root weevil control is when the adult beetles start to emerge from the soil. Weevils feed for about 4 weeks after emerging from their underground pupal chambers. After feeding they begin to lay eggs for the next generation. The best time for control is between when feeding notches first appear on new leaves and the start of egg laying, 4-6 weeks later. For the black vine weevil this period is early summer.

For gardeners interested in a low toxicity approach to black vine weevil control you can disrupt feeding and egg laying in early summer with neem oil insecticides applied to leaves. Then, if necessary, control larvae with fall applications of insect-parasitic nematodes.