Did you ever wonder if the garden fairies were out in your garden at night with pinking shears working on the leaves of your favorite plants? Well, bad news…it’s not the fairies, it’s the Black Vine Weevil. This insect is one of several species of root weevil in our area. The adult weevils first appear in early summer and begin feeding on plant foliage This feeding causes the characteristic notching along the leaf edge that resembles the cut made by pinking shears. You may have noticed damage on plants like Peony, Lilac, Rhododendron, or Rose, although, since this insect isn’t a finicky eater, almost any variety of ornamental plant could be affected. The weevils feed at night and spend their days hiding in leaf litter or in the mulch under the plant. If you want to see one of these insects, go out at night with a flashlight and shake the plant over some white paper. You’ll know you’ve got one when you find a small (0.5 in), oval shaped, black beetle that has a snout. They very closely resemble a Billbug, another root weevil. The leaf damage the Black Vine Weevil causes is unsightly, but won’t normally kill the plant. The problem is the damage that is caused by the developing larvae or grubs. The adult insect lays her eggs in the soil near plants and as the larvae develop, they feed on the plant’s roots and crowns often killing the plant. The adult weevil continues to lay eggs throughout the summer. When fall arrives and the soil cools, the larvae stop feeding and over-winter in the soil. Larval development and pupation continue again in the spring as the soil warms. Adult insect emergence depends on soil temperature so timing varies from year to year.
There are several ways of trying to control this pest; beneficial nematodes have been shown to be effective when used as a drench around the plants that are showing signs of damage. Since these nematodes are microscopic organisms, using them is an act of good faith, so purchase them from a reputable merchant. Apply them in late summer or early fall, after egg laying, but before the soil gets too cold. These nematodes are only harmful to the grubs, not the adult insect and are non- toxic to plants and people when used as directed.
If you choose to use a topical insecticide for the adult insect, spray in the evening after the bees have gone for the day and keep the insecticide off the flowers to help protect our pollinators.
As with any chemical use, follow the label directions carefully.