Here’s why your raspberries are wilting – even though they have plenty of water

In the fruit garden, few things say summer quite like raspberries.

However, two significant insect pests can damage a raspberry patch if not managed properly: the raspberry horntail and the raspberry crown borer. While the symptoms of their presence may be noticeable now, the best times for control are in spring and fall.

Effective management begins with regular monitoring and proactive cultural practices. Both pests spend much of their lives hidden inside the plant, so early detection is crucial for effective control.

It’s relatively easy to differentiate between the two pests by observing the location of the damage on the plant, the physical appearance of the insects, and the nature of the cane’s wilting.

Infestation sites and symptoms

The most visible indicators of the two pests can be identified by examining which part of the cane is affected and how it wilts.

Target area

The raspberry horntail exclusively attacks first-year growth (primocanes). The larvae tunnel upward in a spiraling pattern toward the tips of the canes.

The raspberry crown borer targets the lower cane, crown and upper roots of the plant.

Wilting and damage

The raspberry horntail causes cane tips to soften, wilt and die back. This is typically noticed in June and July. While the tips may recover, they often become crooked and weakened.

The raspberry crown borer causes entire canes to wilt and die. Because the damage occurs at the base, heavily infested canes frequently break off at the crown.

Visible signs

If you suspect you might have a raspberry horntail, look for dark trails from young larvae tunneling just beneath the “skin” (epidermis) of the primocane.

If you think it’s a raspberry crown borer, look for swollen crowns or galls — which are particularly noticeable in October — and sawdust-like frass (insect waste) in the hollowed-out crown area.

Physical characteristics

The adult and larval stages of both pests have distinctly different appearances.

Adults

The raspberry horntail is a narrow-bodied, iridescent black wasp with long antennae, measuring half to three-quarters of an inch long.

The raspberry crown borer is a stout-bodied, clear-winged moth that resembles a yellow jacket wasp, featuring black and yellow bands on its body.

Larvae

Raspberry horntail larvae are white with a brown head and are approximately 1 inch long. A key identifying feature is a short spine on the tail end.

Raspberry crown borer larvae have a white body and reddish-brown head, and grow to 1 to 1.25 inches long. They do not possess a tail spine.

Life cycle differences

The duration of the life cycles of these pests also varies.

The raspberry horntail generally has one generation per year.

The raspberry crown borer has a two-year life cycle, spending most of that time as a larva tunneling deep within the crown and roots.

Control and timing

Effective chemical or biological intervention relies heavily on timing. Start with the least invasive tactics and escalate as necessary.

Cultural control and sanitation

Healthy plants resist pests more effectively. Choose well-drained sites and monitor for nutrient issues like iron chlorosis.

For the raspberry crown borer, start with certified clean nursery stock and avoid transferring canes from infected plantings to new ones. If the crown borer strikes, you should dig up and burn the entire crown.

For the raspberry horntail, select resistant varieties over susceptible ones and prune out wilted cane tips from June to August, cutting 6 inches below the wilt.

Biological control

Parasitic wasps naturally attack raspberry borers and horntails. For the crown borer, apply beneficial nematodes (Steinernema feltiae) as a soil drench in late June to July when the soil is warm and moist.

Soft/organic insecticides

If necessary, try neem oil or azadirachtin (Aza-Direct, Neemix, Neem Oil) or pyrethrins (Pyganic) for either pest. Kaolin clay (Surround) may help repel horntail egg-laying.

Traditional insecticides

To protect pollinators, avoid spraying during bloom.

For the raspberry horntail, target emerging adults in early spring with carbaryl, malathion or permethrin.

For the raspberry crown borer, drench canes and crowns in mid-October or early spring with carbaryl, malathion or acetamiprid.

An imidacloprid soil drench may assist with the horntail, although evidence for its effectiveness is limited.

Brief variety recommendations

Summer raspberries

Look for varieties with resistance to the horntail, good to excellent winter survivability and good quality and yields, such as:

・Royalty

・Cowichan

Note: The popular variety Canby is more susceptible to horntail than both of these varieties, according to research performed by Utah State University Extension.

Early fall bearing varieties

Choose those that will ripen before the season ends and offer quality fruit, such as:

・Polka

・Amira (BP-1) — a recent introduction to be on the lookout for in the coming years.

IMPORTANT: Always read and follow the instructions printed on the pesticide label. The pesticide recommendations in this University of Idaho publication do not substitute for instructions on the label. Pesticide laws and labels change frequently and may have changed since this publication was written. Some pesticides may have been withdrawn or had certain uses prohibited. Use pesticides with care. Do not use a pesticide unless the specific plant, animal or other application site is specifically listed on the label. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.

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