Treating black knot on plum tree
I have a 15 year old Italian plum tree which has widespread black knot. I pruned off all the knots which were visible last year but it came back with a vengence this year. Winter is now upon us and the tree is about to shed its leaves. There are knots on just about all the small branches but the main branches do not have any VISIBLE signs of infection. My intention is as follows:
1. Prune off all branches having visible knots about 8 inches from the knot and clean the pruner with alcool between cuts.
2. Spray all remaining branches with a mix of 70% rubbing alcohol and 10% javel water.
3. Later in the winter, spray with a lime-sulphur fungicide.
My question is: will step #2 actually be helpful or could it hurt the bark of the tree?