I have just detected that a young (3 yr old) plum tree with knot disease. It is mid July and I live in southern Ontario. What actions should I take. So far I have cut off the limbs that display these knots. Is there a spray I could buy here in Ontario which I should spray on the tree now? Also...there is a main limb that has some knots...If I cut this limb off the tree will be quite lopsided...is there any alternatives to cutting this large limb? Thanks so much for your help.