How to Get Rid of Vine Weevils in the Garden

Black vine weevils are a garden invader capable of extensive damage, especially to their preferred woody ornamentals. Active for several weeks in early summer, the adult beetles feed on leafy upper growth, followed by their larvae, the hidden destroyers that feed on roots.

Vine weevils flock to certain trees, shrubs, vines, and perennials. A favored host will have irregular leaf margins filed with notches, while more serious occurrences like wilt occur as stems and roots experience girdling.

To get rid of vine weevils, it helps to know their habits and preferences to offer countermeasures. 

About Black Vine Weevils

In the U.S., black vine weevils arrived from Europe, likely on imported ornamental plants in the 1800s, with confirmation in Connecticut in 1910. They’re a species of root weevils, Otiorhynchus sulcatus (Fabricius), and the most widespread and destructive of the genus.

While leaf damage from the adults in spring and summer is unsightly, it’s the grub phase that is most damaging. Grubs (larvae) are active in fall and winter when they burrow into the crowns to feed on roots. Their continual feeding causes root and stem damage, weakness, and an eventual inability to thrive.

Identification and Life Cycle

The weevil larvae are white and legless with brown heads, and their bodies have a “C” shape. The adult weevils are small, slate gray to black beetles with a prominent, narrow snout. They have subtle yellow markings (actually fine hairs) and dipped areas on the wings.

Adults feed on foliage for three to four weeks before laying hundreds of eggs near the base of their host plants. When the larvae hatch two weeks later, they begin feeding on the roots until cold temperatures drive them deeper. They feed in late summer, fall, and again in early spring.

Signs of Damage

Signs of weevil infestations include wilting stems that occur during prime grub-active seasons of fall and spring. They begin feeding on young, tender roots but become more robust as they develop, moving to thicker roots and stems. Their feeding impedes the plant’s ability to uptake moisture and nutrients.

Leaf damage from adults presents as irregular notches along the margins. While unattractive, the leaf damage seldom injures the specimen.

Scout Regularly

Early detection is the best way to save the plants and manage the pests. Look early and often, starting in late May and continuing into early summer.

If you suspect a problem, as is evident with signs of wilt, notching, or the insects themselves, dig the plants to inspect the roots. You’ll see the white grubs, curved in a “C,” between the roots. This inspection is easier for small and potted selections than it is for established shrubs and trees.

Handpick

The adults are most active at dusk and a few hours after sunset in late spring and early summer. To get rid of vine weevils, try handpicking them off stems and leaves when they’re active in the evening. Since they hide under leaf litter and debris during the day, handpicking in the evening offers the best chance to displace the most insects.

Handpicking the beetles can involve a sweep of the underside of the leaf to easily knock them off. Vine weevils naturally drop to the ground with disturbance, so a quick brush is all that’s needed. Or, shake the stems gently to get the insects to drop. For either technique, use a layer of newspaper, cardboard, or cloth to capture the dropped pests for removal. Toss them in a bucket of soapy water for disposal.

Handpick or shake nightly for a week or so during peak activity. Since the population of adult females may not be high in number, physically removing them from the host plant may be a viable option for decreasing leaf damage and limiting reproduction. 

Add Beneficial Nematodes

Entomopathogenic nematodes offer one of the best biological controls against black vine weevils. The parasitic nematodes applied in early to mid-spring and into fall can establish themselves and prey on larvae. Available at garden centers and online, certain nematode species target the grubs. Species vary in their hosts and soil activity; these don’t damage roots or leaves the way harmful nematode species do. They serve to get rid of vine weevils early in their life cycle.

Look for Heterorhabditis spp. to target black vine weevils. The species travels deeper in the soil to find its hosts.

Water the specimens before and after applying nematodes to activate the microorganisms, and maintain soil moisture for the best activity. Pull back the mulch layer at application to grant them easy access to the root layer.

Apply nematodes only when temperatures are warm (above 55°F/13°C but less than 85°F/29°C). Offer the treatment in three-week intervals through fall. The key application times are in early spring (if warm enough) before larvae emerge and in late summer/early fall as they’re active before cool temperatures.

Entomopathogenic Fungus

Like nematodes, certain fungi offer a biological, non-chemical control. Apply Metarhizium anisopliae (Met 52) as a soil drench before eggs hatch. The timing is about four to five weeks after you start seeing adult beetles or their damage. Adults feed for 21 to 28 days and then lay eggs, which hatch 10 to 14 days later.

Lure Them Into Hiding

Since the weevils are reclusive during the day, setting up a spot for them to take cover gives them a space to congregate for collection. Boards, cardboard, or a burlap collar offer dark respite zones. Uncover them during the day, shaking out the cloth over a bucket of soapy water and stepping on those at the ground level.

Start this in late spring as a means of scouting for the first weevils, giving time to take action before they feed and lay eggs.

Encourage Wildlife

Growing a diversity of plant species helps maintain a balanced garden system by attracting natural pest managers. Birds, frogs, and small mammals are examples of weevil predators, including the adults and the grubs. Ground beetles and others also feed on the pests. 

An array of plants, including natives, draws targeted pollinators and beneficial insects. These then bring the birds and frogs, and the food web continues. Ensure overwintering habitat for year-round garden creatures by not clearing fall leaves. Also, leave certain perennials standing as nesting sites. A diversity of species certainly can’t hurt as a means to help manage destructive pests.

Reduce Optimal Conditions

If you see signs of extensive damage, making the environment less accommodating may help get rid of vine weevils. Pull back mulch from around the base of the host to minimize hiding places and egg protection. It also limits excessive moisture that allows larvae to subsist near the surface.

Moist soils also create inviting situations for the root-feeding larvae. Water only when needed, and as soils dry out a few inches below the soil surface, when suitable. Drier conditions drive the larvae deeper as they seek moisture, while damp ones keep them feeding and girdling roots and stems close to the surface.

If you have a history of these pests, avoid planting their preferred hosts. Steering away from Taxus, Rhododendron, and other top species could mean less damage. Look for species and varieties with resistance, too. Hairy-leaved rhododendrons (indumentum) are less favorable to the weevils than smooth or glabrous types.

Chemical Controls

If you notice extensive damage or high populations, there are insecticides to target adult beetles and drenches for larvae. Apply two rounds early in the season to kill the females before they lay eggs.  Aim for late May through June, spacing the applications 3 weeks apart.