On 01/02/2015 15:47, FrankB wrote:
Yesterday I realised I'd made a serious error in sawing off a major
branch )about 5" thick) of a mature plum tree which had been giving the tree
a lopsided look. I only found out today that you should never prune a plum
tree in winter due to susceptibility to silver leaf disease. If I treat the
cut tomorrow by painting with Bayer 'seal and heal' fungicide will that
prevent the problem arising or will 48 hours exposure to the elements of the
wound already be too late?


It's already potentially too late. Anything nasty will have already
entered the wound. Using a wound treatment now will only seal disease
in. I suggest you wait until the summer and see how the tree reacts.
You may be lucky.
--
Spider.
On high ground in SE London
gardening on heavy clay