Inherited old plum trees with brown rot and black knot
This is my first post so i hope i am following the guidelines.
Anyways, so we moved into a property about 4 years ago. It was an old Italian couples home. Part of the reason we chose it was because it had a garden plot and many different fruit trees (i will post separate questions for those). There was two plum trees. At the time i did not think to get the common or latin names of the trees.
Anyway, since the year we moved in i have not eaten a single plum due to numerous plant diseases. I have battles black knot every year, to the point where the tree now looks like ridiculously strange. I have been cutting the limbs off below where the infected branch was which has resulted in the loss of some major branches and a strange growth pattern. One of the trees contracted black knot near the base of the trunk and i didnt think all the hassle was worth trying to surgically dig in around it to prevent it constricting the trees vascular system. I usually burn the removed parts, but there must be other trees in the area that have it as it comes back every year relentlessly.
Secondly, is the brown rot. This hits hard right around now. It has rained quite heavily infrequently. We had a rain fall that was a record for the amount we received, even surpassing a previous hurricane. Anyway, literally almost every plum is covered with this stuff. I know i should be getting rid of the infected ones but its just about all of them, and i cant even reach the highest branches as the tree is well established and the massive pruning i have taken to it has caused it to skyrocket for the heavens.
I guess my question to those familiar with plums is: is it worth it? Should i cut them down? or is there any hope? In ontario we have strict regulations or fungicides, herbicides, and pesticides. So those are out of the picture. Pretty much all i have left is dormant or horticultural oils. To my knowledge they wont protect from black knot or protect the fruit. Can sulfur be applied to the fruit when the tree has leafed out already?
I can post pictures of the tree to display some of the features if it better helps to diagnose treat. The fruits usually start to produce this yellowish sap then go all moldy looking. The black knot, is well black knot. Brown growth that turn to black. I sterilize between cuts.
PS. There will be other question to follow in regards to some seriously huge apricot trees with canker as well.