A story of the mystery of black knot on plums
I was at an orchard today that I've been managing for almost 20 years. The owner inherited the property from his mother and was raised there some 70+ years ago before going out into the world and making big bucks and returning to take over the family estate.
When I first arrived, there were two plum trees completely overwhelmed with black-knot. I cut them down.
Over the last couple decades I've installed about 8 different varieties of plums- all BK susceptible including the ultimate black-knot magnet, Metheley.
The site is very moist (air-wise), with a large pond bordering one side of the orchard and some of the plums are blocked by trees to the east so it's almost noon when they're first struck by sun. It is also very sheltered from wind. Heavy dew is the norm.
All aspects would suggest a great deal of difficulty in managing black knot, but they are the cleanest plums I manage.
There are even native cherries as the first forest trees on the orchards edge, but strangely they have no black knot I can see either.
Every other site I manage without wide open, dawn to dusk sun has at least some black knot, although not in ratio to the fungus encouraging aspects of any given site.
I doubt there's a pathologist on the planet that could explain the whimsy in which BK runs through my world.