How to Identify and Control Strawberry Root Weevil

One of the hallmark signs of spring is the welcoming taste of fresh strawberries. Unfortunately, this harvest can be ruined by several pest issues, including strawberry root weevil. 

Three different species of weevil have larvae that will feed on the roots of strawberry plants: the Black vine weevil (Otiorhynchus sulcatus), the Rough strawberry root weevil (O. rugosostriatus), and the Strawberry root weevil (O. ovatus).

Since strawberries are perennial plants that go through a period of dormancy in the winter, their roots become a good source of food for weevil larvae during winter and spring. Damaged roots can lead to a season of stunted plant growth or kill the strawberry plant entirely. 

If you are growing strawberries hydroponically or if you are purchasing starts from nurseries in the spring, you will likely not need to worry about a strawberry root weevil infestation. However, these weevils also attack some woody ornamental plants and other berries such as raspberries and blackberries, so keep an eye out.

What is Root Weevil?

The black vine weevil, rough strawberry weevil, and strawberry weevil are common pests for strawberries grown in Europe and North America.

These three species of weevils are hard to tell apart during their larvae stage when they are small white grubs with tan heads. Adult strawberry root weevils and black vine weevils are about 8-10 mm long with reddish-brown or dark brown to black bodies. Strawberry root weevils also have distinctive “elbowed” antennae with a bend in the middle.

The black vine weevil is the largest beetle out of these three species. Weevils can be mistaken for ticks but weevils have three pairs of legs whereas ticks have four. 

Life Cycle

Weevils have one generation per year. Adult weevils cannot fly and they lay clusters of eggs on the soil surface or just below the soil surface from June through September.

The black vine weevil and the strawberry root weevils reproduce asexually, which means all of these weevils are female and capable of laying eggs. Weevils overwinter during their larvae stage and will feed on the roots of host plants like strawberries when temperatures allow.

The larvae will pupate in late spring and become adult beetles in early summer to restart this life cycle. 

Common Habitats

Like many other pests, adult strawberry root weevils are active at night. They are often found at the base of the plant or in the soil during the day and they will climb up plants to feed on leaves after the sun sets. If you suspect that you might have a weevil issue, inspect your plants at night with a flashlight. 

During June through August, weevils can also be found inside homes as accidental invaders. They are not harmful to humans or pets and will not consume food products around the house. If you find weevils inside, sweep or vacuum them up to dispose of them. Or gently place them outdoors. Seal up cracks and openings in your home that may allow them inside.

What Do Weevils Eat?

There are thousands of species of weevils and they are commonly named after their common host plant.

As their names suggest, the strawberry root weevil and the rough strawberry root weevil feed on strawberry plants. The black vine weevils, on the other hand, feed on over 150 different species of plants including strawberries.

Weevils make very distinct notched chew patterns along the edge of leaves and flower petals. While adults feed on foliage or flowers, weevils cause the most damage as larvae that feed on plant roots. 

How to Control Strawberry Root Weevils

Controlling pests starts with understanding their behavior and life cycle. As part of an integrated pest management strategy, the objective should not be to eliminate all weevils from the garden entirely, but rather to control their population and minimize their damage. 

Organic or Chemical Control

Adult strawberry root weevils and black vine weevils can be controlled with several kinds of pyrethroid insecticides. However, bees are very sensitive to these insecticides, even those approved for organic use. Only spray at night and under non-windy conditions to limit damage to other susceptible insect species.

Adult weevils do not all emerge at the same time. If you are planning to use chemicals to control their population, you may have to make multiple applications. Follow the instructions on the product carefully.

Environmental Control

One way to mitigate against strawberry root weevils is to plant strawberries as annuals. You can also use the crop rotation method on strawberry beds with non-host plants such as lettuces to reduce the overall weevil population in the soil. 

Beneficial nematodes have also been shown to be effective against weevils. Specifically, Heterorhabditis spp. and Steinernema spp are parasitic nematodes that feed on beetle larvae.

Apply the nematodes during the late spring or summer near the roots of the host plant and water the area thoroughly. You’ll need to apply when the weather is temperate in two treatments spaced two weeks apart. Maintaining a good moisture level will prevent the nematodes from drying out and increase their effectiveness against weevil larvae. 

Preventing Weevils

Since weevil larvae attack the roots of plants, it can be hard to identify this pest problem until the following spring when you see weak growth. Monitoring adult weevils in the summer might give you a better idea of the pests’ population. 

Inspect the leaves of your plants and go outside with a flashlight to look for feeding females. You can also set up a cardboard ‘trap’ that offers an attractive habitat for these weevils. Remove any weevils by hand if you find them on leaves and dispose of your cardboard trap.

Once you confirm a weevil presence in your garden, you can also use the control methods outlined above. 

Frequently Asked Questions