Kevin,
My Euro plums have more black knot than E plum even though they are in the best planting spot of full sun.
Here are my Bavay setting fruit for the first time.
My J plums are in the back yard near tall trees and get 40-60 % of sun. They have black knot but not as much as E plums.
@RichardRoundTree, I have two grafts of Opal, one on each E plum tree. Both grafts flowered profusely and set fruit abundantly. I thought Mirabelles set fruit like mad. Opal beats them. It sets as many fruit, if not more, and the fruit are also larger.
