This was part of one of the dahlias I dug up today. Anyone have any clue what it is?

I believe that is crown gall - though I have never seen it so big! I am afraid you should toss those.

http://www.dahlias.net/dahwebp...

Oh no, I have no idea now which dahlia it came off of. Of course I threw the gall out. But I divided 43 clumps yesterday. No way to remember!

Oh and it certainly did NOT affect the health of the dahlia, whichever one it was. I only had one sickly dahlia and that was more because of poor placement. I would remember if it came off that plant.

More reading, it is caused by a soil bacterium. So I should not plant dahlias in that spot for at least two years. Now I really wish I knew which one it was. Grrr

The only bright spot is that I read it only enters through a wound.

I'll have to practice better management next year.

I am afraid I don't really know much about it. I remember seeing it on one of my tubers one year, before I understood that it was a disease. I don't remember if I tossed mine or not, and I didn't see it again the following years.

So........I wouldn't worry about it to much. It doesn't seem to spread viruntly from plant to plant.

@jvdubb, I have experienced such growth. I agree with @mandolls.