black knot control on young plum trees

ztomJanuary 8, 2014

I planted about 12 bare root euro plums in the spring of 2013. Several already have black knot. I got them from 4 different nurseries so I think the problem is mine, not any one nursery. There was two huge choke cherry trees next door cut down in the early summer, maybe they were the source and it spread when they fell. Anyway, I don't think I can properly prune several inches back from each knot and still have much tree left. I was thinking of trying the following: mix some powder copper bordeaux with some diluted white latex paint and painting over the whole area after I cut the individual knots out. I figure the diluted latex should hold the copper in place for several months, hopefully keeping any fungus inside the branch from forming on the outside and spreading. Any thoughts on wether this would be worth it, or should I just prune them back to a walking stick? I'm probably going to order black knot resistant Blue Byrd Plum, President Plum and a Kenmore in the spring, but I'd like as many of the trees I planted this year to make it as possible.

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alan haigh

Cut the wounds out conservatively and spray the wounds with chlorathalinil. In the future, cut out the BK as soon as it appears. You are probably wasting your time with other fungicides judging from Cornell recs.

    Bookmark   January 9, 2014 at 6:30AM
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thanks hman!

    Bookmark   January 9, 2014 at 9:01AM
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Scott F Smith(6B/7A MD)

I just cut them out and that worked every time but once when a little came back by one edge; I cut that little bit out and it was all gone. Spraying would help more but for me it was not needed.

I don't consider black knot a major problem, just keep alert and you can nail it. Make sure to look for the green knots as well, thats the color when they first form.


    Bookmark   January 9, 2014 at 10:07PM
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alan haigh

How bad a problem it is depends a lot on the site and region, as you know Scott. Sometimes it is a major hassle to keep up with all the cutting necessary at a couple of sites I manage. I've even had to cut down Methely plums on a couple of occasions because it is a typhoid Mary of black knot. On large trees it can get out of hand on that variety.

A site with high dew, eastern shade and nearby infected cherries is a perfect storm, but sometimes it has been a problem at sites where I couldn't figure the cause. On my property the issue is driven mostly by eastern shade and the plum part of my nursery is now in the best eastern exposure on my site.

For the first ten years I grew plums here it was never a problem, now I have to cut out all the black knot every month during the growing season in my nursery and some of the orchards I manage.

    Bookmark   January 10, 2014 at 6:42AM
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