Treating black knot on plum tree

MDBenoitNovember 7, 2012

Hi folks,

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?


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alan haigh

Both 2 and 3 will not be helpful. Even the most affective synth fungicides have limited efficacy against this disease but chlorathalinal is said to be helpful although it's hard to tell in my experience. It certainly doesn't make a big difference.

You needn't treat with alcohol between wounds if you cut to clean wood. Next year cut out knots as they occur. Keep plum growing with good vigor.

    Bookmark   November 8, 2012 at 9:14AM
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