Antony Greene wrote ...
I don't really have any knowledge of gardening, but am just helping my
grandpa with a problem he's facing right now in his little garden. As
the subject line suggests, he's having a problwm with his onion where
the roots are pink. I've looked up this disease and its actually
called pink root - Pyrenochaeta terrestris. The search results,
however, don't really suggest any practical ways of curing this
disease. My question is, is there a natural (preferred) and/or
chemical solution to this issue?

Anthony, are you posting from the US? The reason I ask is I haven't heard of
this disease (caused by the fungus Phoma terrestris) in the UK yet, but it's
common on the other side of the pond. My understanding is that other than a
long rotation system there isn't much you can do. There are resistant
strains of onions in the US.
You could try sterilising the soil you are to plant onions in, when it's
empty but after it's dug and ready, with armillatox or similar as I know
someone who had some success with subduing White Rot using this method. Give
it a good drenching from a watering can.
Please say you aren't in the UK, I've had enough problems with White Rot
without Pink Root too!

--
Regards
Bob H
17mls W. of London.UK