By Hannah Fraser, Entomologist – Horticulture, OMAFA & Erica Pate, Fruit Crop Specialist, OMAFA
Published September 2025
If borers are hobbling the health of your raspberry canes, take action this fall to help reduce pest pressure going forward. There are two types of borers attacking raspberries and other Rubus species in Ontario: raspberry crown borer (a clearwing moth) and cane borers (two species of beetles). Raspberry crown borer is the most challenging to manage due to narrow windows of opportunity for control and limited availability of registered insecticides in Canada. Coupled with physical removal of infested canes and crowns, fall insecticide applications are the most effective way to reduce populations.
Raspberry crown borer adults are active during the daytime and can sometimes be observed resting on foliage, often as mating pairs. These moths have a wingspan of 25-30 mm and look like a big furry yellowjacket, with alternating black and yellow stripes on the abdomen and thorax. The biology of this pest has not been thoroughly investigated in Ontario, therefore some of the phenology (life stage timing) is based on other regions. Females lay eggs in the summer, from late August to September. Eggs are small (1.5 mm), oval, reddish-brown, and are laid on the underside of leaves, usually near the margin. The eggs hatch several weeks later (mid September through October), with larvae migrating to the base of canes, where they either excavate a small cavity or find a protected place in the bark to overwinter. Early the following spring, larvae move through the cambium and into the crown, where they continue to feed through another entire year. Larvae spend most of their two-year life cycle protected within the plant, feeding on the crown, at the base of the canes, and on larger roots. They are protected from insecticides over most of that period. The longer a field is in production, the higher the risk, especially if the pest is not well-managed. High tunnel and soilless production systems are unlikely to be at risk for infestation.
Feeding by larvae cuts off nutrients and water to canes, reducing plant vigour and yield, causing wilting and breakage at the crown, and allowing for the entry of secondary pathogens. The canes become weak and spindly and fruiting canes often collapse while the fruit is still immature. Recognizing raspberry crown borer infestations early is key to reducing economic injury. Symptoms include wilting or dying primocanes and areas of weak growth in the spring, galls at the base of canes, and sawdust-like material at the crown. By early summer, infested canes will pull out easily from the crown with a sharp tug. Dig up the crown, clip off the canes and cut through the crown to look for frass, larvae, and tunnelling to confirm activity.
Since raspberry crown borer has a two-year life cycle and the larvae are at different stages of development at any given time, you need to target the pest over multiple years. This means applications in the fall to intercept newly hatched larvae as they move down the cane to the base of the crown and again in the following spring before they burrow into the crown. You will need to repeat this process over two consecutive years for effective control.
There is only one active ingredient (chlorantraniliprole) currently labelled for raspberry crown borer control in Canada. Altacor® Max (PCP# 34654) or Shenzi® 400 SC (PCP# 34974) (max 3 applications per year depending on rate) will control hatching eggs and young larvae before they move into the crown. Research by McKern et al. (2006) in Arkansas indicated excellent control (100%) using Altacor drenches with early November timing. In Ontario, begin watching for adults and eggs to time control in late summer. The first spray will likely be needed in mid-September or early October when eggs are hatching, ensuring good coverage of the whole plant (canopy and lower plant). Follow this with a second application in mid to late-October, using a high-volume spray directed at the base of the cane to target larvae before they move into overwintering sites. Making two applications helps address the extended egg-hatch period in the fall. Spring applications target the larvae before they move into the crown; these need to be completed very early, in April, when new shoots are 10-15 cm or less. Altacor Max can be used a maximum of 3 times at the low rate (108 g/ha) or 2 times at the high rate (143 g/ha) – maximum 324 g per hectare per season. Shenzi can be used a maximum of 3 times at the low rate (188 mL/ha) or 2 times at the high rate (250 mL/ha) – maximum 563 mL per hectare per season. Unfortunately, another insecticide that was previously relied upon for crown borer control, Diazinon 50 EC / 500 E, is no longer registered for use on raspberries.
Having only one insecticide registered for managing this pest sets growers up for problems with pesticide resistance, since there are no available rotation partners. Early identification and removal of infested canes needs to become a key component of IPM programs for raspberry crown borer. Dig out and burn infested canes and crowns in the late summer and fall. Where practical, remove alternative hosts, such as wild blackberry and other brambles, from the area around the planting. Summer applications of entomopathogenic nematodes such as Steinernema feltiae that actively hunt raspberry crown borer (even once in the crown) may help to reduce numbers (Capinera, 1986); soils are too cold in the spring for these predators to be effective (McKern et al., 2006). Nematodes have not been evaluated in Ontario for management of raspberry crown borer.
For more information and pictures of raspberry crown borer and injury, visit Ontario.ca/cropIPM.