By Patsychilds
United Kingdom 
we grow flowers for cutting and are currently digging up the dahlia tubers for the winter - we have found some knobbly growths on one tuber and would like advice on what this might be
31 Oct, 2010
Answers
It sounds as if it might be a canker. These form knobly growths on the tuber and can be indicative of fire blight. If this is only on one tuber then I would suggest binning it.
31 Oct, 2010
If the knobs are cauliflower-shaped, it's probably crown gall. Bin--don't compost--the tuber, and replace the soil 30 cm deep and 70 cm wide where it was growing, binning the contaminated soil.
1 Nov, 2010
Previous question
Nothing springs to mind from your description - a photograph would be useful.
31 Oct, 2010