Strawberry blossom weevil, Anthonomus rubi, is an invasive pest affecting a range of plants in North America. This weevil, known for causing significant damage to strawberry and raspberry crops, is primarily found in British Columbia, Canada, where it has become established. Here’s how to identify, prevent, and manage this pest to protect your plants.
What Does the Strawberry Blossom Weevil Look Like?
Identifying the strawberry blossom weevil is crucial for effective management. Adults are small beetles, typically 2.5 to 3 mm long, with a black body covered in fine grey pubescence. Their appearance includes a distinct white patch on the scutellum (a small area at the top of the back) and an elongated rostrum (or snout), making them recognizable among other weevils.
The larvae are C-shaped, creamy white, and about 3.5 mm long with a light brown head. They develop inside flower buds, which typically wither due to the female weevil’s habit of severing the pedicel after laying her eggs. The adults and larvae can be found on various host plants in the Rosaceae family, including strawberries, raspberries, blackberries, and roses.
Where Is the Strawberry Blossom Weevil Found in North America?
The strawberry blossom weevil is currently reported only in the southern parts of British Columbia, particularly in the Fraser Valley. It was first detected in Abbotsford in 2019 and has since spread throughout this region. Its presence is mainly limited to British Columbia, but ongoing surveillance is essential as the weevil could spread to neighboring areas with favorable habitats.
How Does the Strawberry Blossom Weevil Affect Plants?
The weevil’s life cycle involves a single generation per year, with adults emerging in the spring as temperatures rise. Initially, they feed on strawberry leaves, creating small, round holes. Females lay eggs within unopened flower buds, severing the stalk afterward, which causes the buds to wither. This action not only affects strawberry plants but also other Rosaceae members like raspberries and blackberries. Bud damage leads to reduced fruit yield and malformed or unmarketable fruits. Although the primary impact on strawberries has been documented, other crops, including raspberries, can experience up to 38% damage in some cases.
How Can You Avoid the Strawberry Blossom Weevil?
Prevention strategies are critical to controlling the spread and impact of Anthonomus rubi. Here are some recommended methods to limit their presence in your garden or farm:
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Regular Monitoring: Early detection is essential, especially during the spring when adults are active and beginning to lay eggs. Check for weevil feeding damage on leaves and withering flower buds as signs of infestation.
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Mechanical Barriers: Using black plastic mulch around plants has shown potential in reducing bud damage. The high temperatures under the plastic can disrupt the weevil’s life cycle by reducing the survival rate of larvae developing in fallen buds.
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Habitat Management: Clearing dry leaves and plant debris around plants can help limit overwintering spots. Removing damaged buds that fall to the ground can also prevent the larvae from completing their development cycle.
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Plant Selection: Some strawberry and raspberry cultivars may show resistance to bud damage. Although not yet widely available, resistant cultivars are an area of active research.
How Do You Control and Get Rid of the Strawberry Blossom Weevil?
Effective control measures for strawberry blossom weevils involve integrated pest management (IPM) techniques that combine chemical, mechanical, and biological controls:
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Chemical Controls: While specific insecticides for A. rubi are not yet registered in Canada, similar weevils in North America, like Anthonomus signatus, are targeted with pyrethroids (cypermethrin, lambda-cyhalothrin) and the insect growth regulator Novaluron. Application of spinosad, a microbial insecticide, has shown effectiveness in trials and could be considered where permitted. It’s important to apply these treatments early in the growing season when adults are active and before they start laying eggs.
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Biological Control: Research in Canada has initiated studies on natural enemies of A. rubi. Pteromalus parasitoids, a type of tiny wasp, have been observed attacking weevil larvae in damaged buds of strawberries and other host plants in British Columbia. These parasitoids may offer a promising biological control option, although further study is required to assess their impact fully.
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Predators and Natural Enemies: Predation by midge larvae and potential predatory carabid beetles has been noted. Although these predators are not yet part of an established control program, ongoing research aims to determine their role in managing A. rubi populations in the field.
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Crop Sanitation and Field Management: Practices such as burning leaf litter in strawberry beds, plowing over fields with severe damage, and removing damaged buds from beneath plants can help reduce the weevil population. These methods are particularly useful in small-scale or home gardening settings, though they may be less cost-effective in commercial farming.
How Can You Detect Strawberry Blossom Weevil Infestation?
Detection relies on observing the characteristic damage caused by A. rubi. Look for buds that appear partially or fully withered, often with small punctures at the base. These punctures are the result of the female weevil’s egg-laying process. Buds that fall off are another indicator of infestation.
In some cases, eggs are laid in open flowers, and larvae development within these flowers leads to distorted fruits with scarring, rot, or mold. Damaged buds and flowers generally yield unmarketable fruit, contributing to potential economic losses. Early and consistent monitoring is the best approach to identify and manage A. rubi in affected areas.
By recognizing the signs of infestation and implementing these control strategies, North American growers can better manage the impact of the strawberry blossom weevil on their crops.