London,
United Kingdom 
I've just dug up an unhappy looking Phlox which I put in last year, and discovered that the roots are light brown and look like saw dust. I think it may be Cotton Root Rot (one of its names) after googling for diseased root info. Should I destroy the plant? How should i treat the area of soil where it was planted?
Many thanks
2 May, 2011
Answers
Well that's a relief. But I think it's more than just lack of moisture. I moved another one just before (from a different place) which was definitely in a too hot and dry position and the roots looked fine. I'll post a photo of the roots of the affected one - they look horrible - like saw dust...
Many thanks x
2 May, 2011
Cotton root rot is a perennial problem here, but, as far as I know, it is still restricted to alkaline soils in the mild winter, hot summer areas of the North American Southwest--count your blessings!
3 May, 2011
That's a relief - thank you!
3 May, 2011
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As far as I'm aware cotton root rot is not a problem in the UK, but in warmer parts of the US and Mexico. Phlox hate to dry out and will wilt at the first hint of dry soil, so the usual problem with them is, in fact, drought.
2 May, 2011