[julietmaria]

I was hoping to make a liquid feed from my comfrey leaves but as I cut them I noticed that a lot were covered in a dark yellow powder, particularly on the underside.  I am assuming this must be some kind of rust and decided I should not use to make a fertalizer as this may well pass on the disease to other plants - was I right?  And does anyone know what the yellow powder is and how I can stop it happening again?  Thanks Juliet

[John]

I've not come across this but I would have thought making a liquid comfrey fertiliser would kill off the rust which I think is specific to comfrey from your description (Melampsorella symphyti) and generally only effects wild comfrey.
L D Hills suggests the best thing to do with the comfrey in these circumstances is to kill off the patch and dispose of the plants then replant Bocking 14 elsewhere.
Since he wrote that we have systemic fungicides available and I would be tempted to try a spray with Dithane although not approved for the usage.

[WG.]

Good call John ... http://www.gardenorganic.org.uk/factsheets/dc5.php

If you are organic JM (please update your profile so that we can all see how to reply.  It helps to know where you are (approx) and whether you are seeking remedies considered to be organic.) then replacing the plants is the only real option