Like the other posts indicated, welcome to the exciting world of Black Knot. I have been struggling to find resistant varieties for the past 10 years in upstate NY, zone 5. It does limit some varieties to try, but having some success. As I cycle through every variety I can try, the standouts are pretty clear. While the Stanley Plum (the worst for black knot) had every twig infected with galls, 10 feet away, my Superior still has none going on 12 yrs old. My Alderman of the same age still has none. For newer trees that are several years old, Maneta, Early Italian, Toka, and Au Rubrum are free of any sign of Black Knot.
I was disappointed this spring to find my Oblinaja and Seneca had several knots forming . Supposedly The President is supposed to be very resistant or even the most resistant. I planted one about 20 feet from a wild Black Cherry tree that always has it and it did get a gall last year that I cut off and nothing has come back this year. Im starting to think that the young sapling trees are more susceptible to Black knot and may be able to fight it off as they mature. I also had two Bluebyrds that I ripped out last year as saplings that were covered in knots in one year, but Ive gotten another this spring on the off chance they were mislabeled at the seller.
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