Cure or prevention for rust on garlic?

I am looking for a cure for or prevention of rust on garlic.  My garlic gets it every year but doesn't seem to affect onions or leeks until much later in the year if I leave my garlic around which is already rusted.

The main problem, apart from affecting growth of the bulb is it makes it impossible to know when to lift the garlic as foliage die back is affected prematurely and there is nothing to judge by.

I think I need to harvest by tomorrow though to prevent rust spread to my onions.

As soon as you see the rust on the leaves smear the area with petroleum jelly. It stop's the spore's infecting other plant's.

The rhs has some advice

http://apps.rhs.org.uk/advicesearch/Profile.aspx?pid=214 :

• Infection is worse on nitrogen-rich soils with low potassium, so take care with fertiliser applications

I've been adding potash as a spring dressing round my overwintered garlic (and onions), and this seems to keep rust at bay.  I never seem to get it right with leeks though - maybe I'm just so eager to get them dibbed and out the way that I forget about the potash

Note to self then for next year - garlic needs Comfrey tea not Nettle tea!