Raspberry Crown Borer: Essential Guide to Identification, Control, and Prevention

Raspberry Crown Borer is a common pest affecting raspberry plants, causing damage to canes and potentially reducing crop yields. The adult borer is a striking black and yellow moth, resembling a yellow jacket in color, and it flies during the daytime. In some individuals, the yellow can be quite bright, while in others it is almost white [1].

This pest attacks raspberry plants in a two-year life cycle. In the first year, its larvae burrow into the cane’s tips where the damage might not significantly affect the overall plant. However, in the second year, the larvae move downward to the plant’s crown and could cause more severe damage, such as premature dying of canes and reduced leaf size [2].

Raspberry Crown Borer Identification

Adult Moth Characteristics

The adult raspberry crown borer moth is a black and yellow moth that measures 10 to 15mm (3/8 to 5/8 inch) long. The moth is known for its striking resemblance to a yellow jacket. Some key characteristics include:

• Bright yellow or almost white bands
• Clearwing moth with feathery antennae
• Flies during the daytime

Larvae and Eggs

Raspberry crown borer larvae are large (1/2-inch to 3/4-inch) and tunnel into the plant’s base, causing damage to the canes. The brown oval eggs are laid on the underside of the raspberry leaf.

Similar Pests

Raspberry crown borers can be easily confused with yellow jacket wasps. However, adult moths have scales on their body and wings, while yellow jacket wasps do not. Here’s a comparison table:

By understanding the adult moth characteristics, larvae and eggs, and similar pests, identifying raspberry crown borers in your garden can be much easier.

Life Cycle and Biology

Two-Year Life Cycle

The Raspberry Crown Borer (Pennisetia marginata) has a unique two-year life cycle. Adult moths emerge during the summer months, typically from July to September¹. They lay their eggs on the undersides of raspberry leaves, and the larvae hatch and begin to feed. They then tunnel into the lower part of the raspberry cane, where they continue to develop throughout the winter months.

Overwintering

• Larval stage: Raspberry Crown Borer larvae overwinter inside the raspberry canes.
• Spring emergence: In the spring, usually around May, these white larvae with brown heads continue feeding, weakening the canes and causing damage².

Pupation Period

During the pupation period, larvae change into adult Raspberry Crown Borers. This transformation takes place within the cane itself, specifically, near the base of the raspberry plant. After they emerge as adults, these moths, resembling yellow jacket wasps, start the next generation’s life cycle³.

Comparison Table: Life Cycle Stages

Damage and Symptoms

Affected Canes and Crowns

The Raspberry Crown Borer mainly affects the canes and crowns of raspberry plants. Infested canes exhibit premature dying, spindly growth, and swelling at the base. You may also notice sawdust-like frass near the soil, indicating the presence of larvae.

Leaves and Roots

In addition to canes and crowns, infestations can cause reduced leaf size. However, the damage to leaves and roots is minimal compared to the damage to canes and crowns.

Reduced Productivity

Infestations of the Raspberry Crown Borer have a detrimental impact on the productivity of raspberry plants. Their damage to the canes and crowns leads to a decrease in overall plant health and vigor. Thus, it is crucial to identify and address infestations early on to minimize their impact on your raspberry crop.

Characteristics of Raspberry Crown Borer damage:

• Premature cane death
• Stunted cane growth
• Swelling at cane base
• Sawdust-like frass
• Reduced leaf size

Prevention and Management

Cultural Control

One effective way to manage Raspberry Crown Borers is through cultural control. Start by removing wild brambles near your raspberry plants, as these can harbor pests and diseases¹. Pruning and cane removal activities are essential, as it helps you monitor for tunnels in the cane base, which indicates borer activity². Also consider:

• Regularly inspecting your plants, especially during the growing season
• Ensuring proper sanitation by cleaning up fallen plant debris and trimming weak or damaged canes
• Planting resistant varieties when available

Biological Control

Biological control involves using the pest’s natural enemies to reduce their populations. For instance, using nematodes like Heterorhabditis bacteriophora³ can help control Raspberry Crown Borer larvae. These beneficial worm-like organisms can enter the borer’s body and release bacteria, killing the pest.

Advantages of biological control:

• Eco-friendly and safe for bees and other pollinators
• Compatible with other pest management methods
• Minimizes the need for chemical control

Disadvantages of biological control:

• May be less effective in reducing large infestations
• Requires precise application and monitoring
• May be more expensive and labor-intensive

Chemical Control

Chemical control should be the last resort when other methods are not sufficient. Always choose a pesticide registered for use on raspberries⁴ and follow label instructions to ensure its proper application. Chemical control options for the Raspberry Crown Borer include:

• Diazinon: A broad-spectrum insecticide suitable for both commercial and home use⁵. However, keep in mind that it can be harmful to beneficial insects and aquatic life.
• Other insecticides: Available for raspberry pest control, but always read the label for specific directions and restrictions.

Remember that chemical control should be applied responsibly to minimize harm to the environment and other organisms, such as pollinators.