Blackberry borers

Asked December 12, 2015, 2:26 PM EST

My care of the blackberries was a little behind last summer and many of the canes have the grooved swellings from cane borers at the base on the new canes. If I sacrifice them I will loose 2/3 of the canes. Is better to keep them and try to watch to remove involved canes early next summer, or cut them out and destroy those canes now? Thanks

Jefferson County Kentucky insect issues insect damage blackberries

4 Responses

This damage appears to be caused the red-cane borer. Borer larvae cause damage as they grow and feed inside the cane. At this time of year, they can only be controlled by cutting out the affected canes and destroying them. Infested canes usually die or are severally weakened by the insect.

The adults emerge in May and June. The adult borer can be controlled with insecticides, right before the blackberries bloom or immediately after the fruit is harvested. They are a red and black beetle with a flat head.

Our publication on growing blackberries and raspberries has more details on controlling insect and disease problems:
http://www2.ca.uky.edu/agc/pubs/ho/ho15/ho15.pdf

Feel free to contact our office if you have other questions.

Let me know if I can help you further!


Carol Wilder
Horticulture Technician
Jefferson County Cooperative Extension Service
502-569-2344
810 Barret Ave
Louisville KY 40204




Thank you for your assistance. I don’t expect you to spend time answering my further questions, but I would like to share my thoughts for other gardeners.

I had seen some of the information on the cane borer, and the advice to destroy the canes. However, when the majority of canes are affected that is very destructive of next summer’s crop. Some of my canes were allowed to grow over tall, they are 6-10 feet high (had to put up some tall posts to keep them in their bed). As such not all of the galls are at the base, but some on branches. I could not find out how far and in what direction the larva travels. I would like to be able to spare any portion of the canes that does not contain a larva.

I also wondered if there was not some way to destroy the larva, or the pupa later in the year before they emerge. That way I could keep the canes even if they were less productive. As a gardener any crop is better than none. I did find an article on Google that some varieties of upright blackberries that were infected produced better than others, but mine are Apache, and this was not one of the tested varieties, so I do not know what the effect of the galls will be. The canes look healthy now.

I know that a large part of the problem is the need to destroy the many wild brambles in the area. How feasible this depends on how far the clear zone should be. I could not find any information on how the adult beetle senses the target or how far they travel to find a target cane.

Controlling propagation of the beetles is a priority. Since the larvae go directly from the egg into the cane, they are protected from predation, but is there anything that kills or eats the eggs. Just to make things more complicated, I try to garden organically, or at the least use IPM. I am not sure what I would spray when the beetles emerge, as some websites suggest malathion which I would avoid. I could not find out the best predators for the cane beetle or its eggs.

If I keep some canes with galls, can I prevent the adult beetles from emerging? I could not find out if a gall is from one larva or many. In fact in cutting the canes in half I could not even find a larva in them (they are supposed to be white and 11mm long). Do they all survive to pupate, or do some die in the cane or gall?

I would appreciate any tips on researching details. Most advice on line is general and similar, but does not provide great biological detail. Part of the pleasure of the garden beside the culinary uses (and my garden is all about food), is the biology. I have access to some journals via the Internet, but I find it hard to search for the details of the ecology of the pests and plants I grow. The published peer reviewed articles are often very narrow and the molecular techniques outside of what I have available. How does a gardener get good ecological information?

Thanks



Borers are very hard to control on plants because they are doing damage as they grow and feed inside the plant where we cannot see or easily manage them. Especially on crops or plants that we eat as we are restricted on the insecticides we can safely use. So that means using pesticides that are not very strong or using other measures to control the adult insect. The most organic way to control these insects is to cut the canes affected and destroying them.

The adults mate and lay eggs right before the berries bloom (May-June). The eggs hatch as tiny larvae and burrow into the cane but did the damage you see now, during this last growing season. The canes that are infested will either die or be very weak so they are not going to produce anyway. Cutting those canes out now will help prevent infestation NEXT year.

As you know, there is not a way to kill the larvae once the eggs hatch and the larvae burrow inside the cane without heavy chemical use. The photo shows how much damage they can do to the tissue of the blackberries infested.

Dr Ric Bessin, UofK Extension Entomologist, has a publication on these insects:
http://www2.ca.uky.edu/entomology/entfacts/entfactpdf/ef209.pdf

Please feel free to call me if you would like to discuss this topic further.


Carol
Horticulture Technician
Jefferson County Cooperative Extension Service
email: carol.wilder@uky.edu ph: 502-569-2344





Carol,
Thanks, the extension article was very helpful. The larva travel 6 " below to 25" above the gall, and many are destroyed by fungus, parasitic wasps, and unknown causes. I may leave some in place and try to put the cane in a sleeve of plastic tight at each end to see how many beetles hatch. I could look just look for "D" shaped exits, but then they would be free to reproduce again. I will trim most out and try to follow the full length to see if I can find the larva. If I can find them, I will try to section and make a slide to see if they have fungus, wasp or other findings. I will keep an eye out for degenerated larva particularly. I wonder where they pick up the fungus and if that effect can be enhanced. I will keep you informed. Bob