Blackberry Gall

I recently noticed what looks like a gall on one of my blackberry canes. An internet search for possible causes revealed blackberry cane gall and blackberry knot gall, but I’m not sure if it’s either of these or something else.

Does anyone know what this is and what, if anything, I should do.



not sure but id definitely cut that cane out and burn it.


Yes, cutting the cane out is probably a good idea, but depending on the cause it might be best to remove the entire plant. Blackberry Cane Gaul is a bacterial infection which requires removal of the entire plant whereas Blackberry Knot Gall is caused by wasp larvae and is relatively harmless to the plant.

Internet searches are helpful with issues like this, but sometimes it takes someone with experience to make the correct call. I was hoping someone here might have that experience and be able to help me decide what to do. We’re coming off a holiday weekend, so many of the regular contributors to this forum may not have been active here for several days.

As a side note, I am waiting for a reply on this question from my local Cooperative Extension and see that the Master Gardener initially assigned the question has passed it on to the Extension Agent. From this I assume it’s a difficult question to answer. I’ll post an update when I hear from them.



The extension agent replied that he thinks the gall is likely caused by rednecked cane borer, but I’m not sure I agree. The few photos I’ve found on the internet of brambles infected with rednecked cane borers show a swollen area of the cane rather than a gall. Here’s an example from the Missouri Botanical Garden.

I think it looks more like Blackberry Knot Gall as seen in BugGuide and Nature Watch.

I cut the gall out and opened it up. Here are a few photos.

First cut to open it up:

Another cut showing two larvae:


Well, the gall was certainly not caused by a bacteria, so I can rule out Bacterial Cane Gall, which would have required removing the entire plant. Whether the cause is rednecked borers or a wasp really doesn’t matter at this point as I have removed the gall and associated larvae, though I’m leaning towards the wasp.

What do you think? Does anyone here have experience with these pests that you can share?

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A final update

A week or two back my extension agent forwarded information and pictures of the gall and larvae to the Plant Disease & Insect Clinic at NC State University. Today, he sent me their findings which I pasted below. (edited for clarity and to remove personal information)

It confirms what I suspected, Blackberry Knot Gall caused by the wasp Diastrophus nebulosus. I am fortunate to have the NC Cooperative Extension available and willing to help when confronted with a problem not easily solved by and internet search. Now I know the cause and proper plan of action for future reference.


Plant Disease & Insect Clinic · Plant Pathology · Entomology
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Sample Report

Please print a copy of this page for your records and to include when submitting a physical sample
Sample Number 34733
Date Entered 2019-12-19 09:11:24
Host: Blackberry (Rubus sp./spp.)
Variety: not sure but thornless
Invoice Status: $0 FREE_SAMPLE (N/A)
This sample report is provided free of charge to your agency as an educational sample.
Collected By: CLIENT
Date Collected: 2019-12-09
Host Site Type: HOME GROUNDS
Host Address: CLIENT
Problem Type: UNSURE
Expect Physical Sample: NO
Disease Symptoms: GALLS
Disease Distribution: LOCALIZED
Site Conditions: SUNNY SITE
Disease Parts Affected: STEMS
Disease Percent Affected: 10%
Insect Signs: Galls
Insect Doing: Looks like larvae inside the gall in
picture of cross cut gall
Insect Degree of Infestation

Sample Result #1
Date Entered 2019-12-19
Description blackberry knot gall wasp
Pest Gall wasps (Family Cynipidae)

Findings — Matthew B @ Thu Dec 19 2019 11:37:54 GMT-0500 (Eastern Standard Time) —

This is a gall made by a wasp, and almost certainly the blackberry knot gall wasp (Cynipidae: Diastrophus nebulosus ).

Thanks for the info on this. Good photos and an excellent future reference. I never seen this, just the borers, and the swellings look nothing like your gall. Those wasps have a lot of gall to attack your plant! :slight_smile:

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