Vine Weevils in the Vegetable Garden
Vine Weevils are common all around the world. They can be found most easily in two forms: larvae and adults. As larvae they appear as small grubs in the soil where they can feed on your plants root system. As adults they chew on leaf margins.
This damage is not as harmful, however it is easier to identify the pests' presence. They commonly feed on ornamental plants such as yews, arborvitae, euonymus, and hydrangeas while also being a threat to fruits and vegetables.
The real threat is when they are in their larval stage as grubs. As adults, while their damage is not pleasant to the eye, it is not detrimental to your garden's success.
Facts About Vine Weevil Garden Pests
- Vine Weevil Distribution: Invasive to nurseries, greenhouses, and gardens throughout the world
- Vine Weevil Host Plants: Evergreens such as rhododendron, azalea, rose, and nearly any greenhouse container annual
- Vine Weevil Lifespan: ~10-12 months (2-3 months as adults)
- Vine Weevil Eggs Laid per Lifetime: ~250-500
- Vine Weevil Removal: Sticky traps, diatomaceous earth, mulch, pesticides containing Bifenthrin or Beauveria bassiana
- Vine Weevil Predators: Nematodes, roundworms, birds, spiders, grasshoppers, chickens
- Most Common Vine Weevil in North America: Black Vine Weevil (Otiorhynchus sulcatus)
What Do Vine Weevils Look Like?
As larvae they are white, legless grubs with pale brown heads and about 10mm long. While in their larval stages they can be found burrowing in the soil after hatching from their eggs at the crowns of their host plants.
As larvae they prefer to stay in moist soils such as can be found in container gardening. In the spring to summer months adults appear as gray/black beetles with short and broad snouts, bent antennae, and patches of hair on their wings.
Their bodies measure about .5-1” long. While they have wings they are flightless insects which primarily can be found in the soil, compost, or rocks during the day and emerging at night. When identifying Vine Weevils become familiar with other beneficial insects such as ground and rove beetles to be sure and keep them around.
Vine Weevil Damage to Garden Vegetables
Weevil damage is fairly easy to identify because chewing marks to leaves look like nothing else in the garden. Vine weevils exclusively chew on the perimeter of the leaf, causing it to appear notched similar to an arrow or spearhead.
Vine weevils are one of the few insects where both the undeveloped larvae and the adult will feed aggressively on host plants. Adult weevils cause damage to leaf margins by chewing at night, rarely being caught or seen with the naked eye.
Their larvae however cause the greatest amount of damage as they feed on plant roots causing wilt, even if well watered due to the inability of your plants to adequately take up water and nutrients. This damage can lead to stunted growth or even death in the fall to spring months. Moist soils are a sanctuary for vine weevil grubs to destroy your root systems.
What Do Vine Weevils Eat in the Garden?
While there are several types of weevils found throughout the world, they almost exclusively feed on evergreen perennials such as rhododendron, yew, azalea, lilac, rose, apple, and nearly any kind of potted greenhouse annual.
The Vegetable Weevil is found on many common garden crops in the western states. Adult vine weevils eat leaves while grubs eat roots. There is not much discrimination between what plants are likely to be eaten.
While most plants are susceptible there are a few that are more likely to be infested than others as noted above. Adults almost exclusively stick to eating leaves, as their chewing marks leave a half moon shape or a small trail in the leaf margins that get a thin dry border around them.
Vine Weevil Eggs
Female vine weevil adults come out of the soil in late spring to early summer before feeding on plant material for 3-6 weeks. Then they start laying their eggs near potential host plants and are able to lay about 250-500 eggs during their 90-day adult life.
Their eggs are white for the first day after being laid before starting to brown. The eggs are spherical and very small measuring only 0.7mm in diameter.
The laid eggs hatch after 2-3 weeks allowing the larvae to burrow into the soil to feed on available roots. The larvae mature to about ¾ inch long before overwintering and pupation in the spring. The pupa are white with small spines on the head, abdomen, and legs. From this stage they will develop into an adult.
How To Rid Vine Weevils from the Garden
Cabbage loopers are easier to remove from the garden because they are smaller, softer, and have more predators than larger beetles or hornworms.
The best times to check for a vine weevil infestation is to observe chewing marks on the leaves or to inspect plants in the early morning or at night. In greenhouses or nurseries check under pots and the underside of benches during the day.
Sticky traps and barriers are a good way to catch living adults as they travel via crawling since their wings are flightless. If natural wildlife has access to your garden or nursery natural predators may also aid in controlling the population.
If composting, check regularly for grub infestations that could harm your gardens when applied. For grub infestations diatomaceous earth is a good option to control larval populations.
Nematodes are another option but work best in moist and light soils and can also be used within traps to affect adult populations.