Dahlia Gall - Ask Extension
I have a bed of dahlia tubers that I overwintered in the ground. I started digging them to divide last week and found some obvious gall (1st photo sin...
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Dahlia Gall #928194
Asked April 13, 2026, 12:15 AM EDT
I have a bed of dahlia tubers that I overwintered in the ground. I started digging them to divide last week and found some obvious gall (1st photo single tuber). I have been digging the dahlias in the same bed and inspecting them for fall as well. I found this large clump that looks suspicious (2nd photo of many tubers in a clump) could you confirm if this is gall?
Then this third clump with three tubers is from another bed but now I am questioning if this is gall… I dug it up a couple weeks ago so it’s much drier but I didn’t think anything of it at the time. (3rd photo)
Lane County Oregon
Expert Response
Thank you for contacting "ask extension" with your question about dahlia galls. I forwarded your pictures to one of our dahlia experts.
1. You correctly identified the first picture as a gall--
2. The second photo is inconclusive. We need to wait until the eyes sprout. If they have multiple shoots per eye then the gall bacteria is present. If it's a single shoot, then it's healthy,
3. The third picture is of a healthy tuber.
You can find images and more information about this disease in the Pacific Northwest Plant Disease Management Handbook: (https://pnwhandbooks.org/plantdisease/host-disease/dahlia-crown-gall).
Crown gall is not treatable and spreads easily. If you suspect a tuber has crown gall, discard it. Sterilize all tools used on the infected plant before using them on other dahlia tubers.
Hope this helps!
1. You correctly identified the first picture as a gall--
2. The second photo is inconclusive. We need to wait until the eyes sprout. If they have multiple shoots per eye then the gall bacteria is present. If it's a single shoot, then it's healthy,
3. The third picture is of a healthy tuber.
You can find images and more information about this disease in the Pacific Northwest Plant Disease Management Handbook: (https://pnwhandbooks.org/plantdisease/host-disease/dahlia-crown-gall).
Crown gall is not treatable and spreads easily. If you suspect a tuber has crown gall, discard it. Sterilize all tools used on the infected plant before using them on other dahlia tubers.
Hope this helps!
