"From: Hannah Burrack, Extension Entomologist
Blackberry Borers Can Mean Big Problems
Gina Fernandez, the North Carolina State University caneberry specialist, has just returned from sabbatical and has wasted no time getting out for field visits. Yesterday, she brought me several samples from blackberry fields in Guilford County that were in severe decline. Their problems were almost all insect related. There were more cane boring pests from these few sites than I have seen my entire time at North Carolina State University! I'd like to use these samples as an overview of the key cane boring insects in North Carolina, what symptoms to look for, and what the management strategies for these pests should entail.
Evidence of borer damage is often visible from a distance. Plants will appear weakened, and in the case of raspberry crown borer, floricanes will be loose and easily removed. There are 3 key cane boring insects in North Carolina, and these locations had all of them!
Rednecked Cane Borer
The rednecked cane borer (Agrilus ruficollis) is part of a family of beetles known as metallic wood boring beetles. The adults (http://www.ca.uky.edu/
Low levels of rednecked cane borers can be managed with cultural control, specifically by removing and destroying all infested canes during the fall. The larvae overwinter inside the cane, so pruning will remove next year's generation of adults. For large infestations, chemical control of the adults may be necessary (for chemical information, see the Southern Region Brambles IPM Guide online at http://www.smallfruits.org/
Raspberry Cane Borer
Raspberry cane borers (Oberea bimaculata), members of a family known as long horned beetles due their prominent antennae (http://www.virginiafruit.
Cultural control, via pruning, is also an effective means of managing raspberry caneborers. Insecticide treatments may be targeted to the emerging and ovipositing (egg laying) adults just after bloom in cases where large infestation exist.
Raspberry Crown Borer
Raspberry crown borer (Pennisetia marginata) is perhaps the most severe pest of caneberries in the southeast. The larvae of this clearwing moth feed on the roots and crowns of caneberry plants and can kill an entire plant. Because they spend most of their 1 to 2 year larval stage underground, they are extremely hard to manage. Work conducted in Arkansas demonstrated that late fall or early spring soil drench pesticide treatments are most effective at reducing raspberry crown borers. These timed treatments target the early instar larvae before they are ensconced in the crown.
Insecticides are, at this time, the most effective means of raspberry crown borer management. Infested plants should be completely removed, since mature larvae will not be impacted by pesticide treatments.
In addition to the damage caused by these three wood boring insects, there were also several canes with damage at the tip that were dying back.
It is possible that this damage was cause by raspberry cane borers, but no larvae were found in the canes, and what tunnels there were stopped several inches from the top. If this was raspberry cane borer injury, we would expect to see tunnels continuing to the soil level or larvae present. These canes may have been injured during tipping and then feed on be opportunistic secondary pests. I dissected one of these canes, and there was fungal growth in the gallery, although this may also be secondary.
Wood boring insects are a fact of life for caneberry growers and can easily get out of control if a planting is not management carefully. There are abundant feral and wild brambles in the landscape, which serve as hosts for all three of these insects. Carefully scouting, good cultural management, and insecticide treatment when needed will keep borers from destroying caneberry plantings.
For the latest information on insect management in small fruits in North Carolina, see the NC Small Fruit, Specialty Crop, and Tobacco IPM blog at http://ncsmallfruitsipm.