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["Alan Haigh" <alandhaigh@gmail.com>]

I don't know how our black-knot issues compare to other parts of USA and Canada.  We have lots of native cherries spreading the innoculum and some black-knot is almost always going to appear on most plums.  I grow Mt Royal on just 2 sites and have only been around when ripe fruit was available once.  I was unimpressed taste-wise compared to many we can grow here.  Black-knot-wise I think I've had to cut some out on this variety.  Never grown the German prune-plum because it's not sold by my suppliers.

 

Black knot seldom is a serious issue here as long as the site has a reasonable amount of eastern exposure to dry off the dew quickly and you keep the trees vigorous (grow 'em on myro) while removing knot as it appears.  Of euro-types I've grown, only Damson has seemed particulary vulnerable, maybe becuase it's so brushy.  I'm sorry that I haven't kept more notes on relative resistance, but it just hasn't been that crucial for me.

 

It is the Japs that suffer the most and of these, Methely is the ultimate bk magnet.  I once cut a mature tree down on my own property because I couldn't keep up and it was spreading to surrounding nursery trees.  Elephant Heart picks up a lot also.  Fortune seems relatively resistant and is a great plum here based on a mere 2 years of harvests.  Totally upright grower though, so you better tie down the branches.