Allotments 4 All

Can anyone tell me what this is and whether I need to worry about it?  ???

It's on the new growth of one my first earlies (Swift) but hasn't spread to the other three varieties yet (Red DOY, Lady Crystl, Mimi). Only affecting the tops/recent growth so far.

see recent thread ..

http://www.allotments4all.co.uk/smf/index.php?topic=32210.0

Thanks bak, missed that thread.