I manage so many contrasting sites as far as black knot infections go it really defies easy explanation about best managment or cause. Some sites with infected cherries nearby and no morning sun will not have a big issue and another with wide open light and no nearby native cherries will have galls almost impossible to control. I've had to cut down mature trees (goddam Methely- the ultimate gall magnate) just to save other varieties. Scott, I wish an open tree was a panacea. Methely tends to grow leaves all along its wood and even when I keep them open and repeatedly cut out those little spurs that shade the wood I have had a lot of trouble the last couple years. Last years relentless rain just made it all the more difficult. I have saved large trees completely overwhelmed with the cancer by doing what was mentioned- drastically heading back to pretty large wood. It was a Santa Rosa. Don't think it would work with Methely. Olpea, I cut out galls at sites last fall where there were new galls this spring, and I even cut out the swollen early infections when I see them. After we went over this last season I decided to follow your advice and go back to spraying with chlorothalonil. I also keep a small bottle and spray the wounds. I had stopped doing this because it seemed unecessary for a few years but when it's really wet it may be helpful. The good news is we're having a drought spring- my prayers have been answered. Maybe in a couple weeks I'll be praying for rain. Right now I'm just hoping for no hard frosts.

Unfortunately here in Ontario we have quite strict regulations on pesticides, herbicides, and fungicides. It is the brown rot that really gets the fruit. Im not sure what i can do to quell it besides a dormant spray or serenade. I suppose that at this stage the tree may be so worn down and infected it may not be worth it. Is there a limited time span on plum trees?

What you should do is contact the appropriate local agency in Ontario. Here in the US we have two resources: state university ag extension, and state forestry services. But in the meantime I can tell you about my experiences with this black knot fungus. I am a timberland owner and my most valuable product is high quality black cherry logs, especially veneer grade logs. These are very valuable and can bring $6 per or more per board foot in the log Black knot fungus is common in my woods and I have done little or nothing to try to control it. Usually it is not a problem. Occasionally it will get into the trunk of a tree and cause a serious canker. This normally does not kill the tree, but in a rare case it will weaken the trunk and the tree may break. Usually, however, it just serves to degrade the log, but most times I can buck the log at so I cut out the canker and the loss is minimal. These cankers are not the source of any rot that progresses through the tree. Most of the time the fungus causes small cankers on twigs, this kills the twigs and they die and fall off. In a few cases I have seen an individual tree with hundreds of these twig cankers on them, and then a few years later they are all gone and the tree in unaffected. Many trees never seem to get any infections at all. So, what I am tellling you is, you probably do not have a serious problem. If you can reach and prune off the cankers, and dispose of them so no spores are released, I would do that. If you have a tree growing with a canker on the trunk, you may want to cut that tree down if it will make more room for a better tree to grow. But a tree with a black knot canker on its trunk can live a long time and produce much valuable wood and/or provide the other kinds of benefits a good black cherry tree can provide. But you need to check with whatever agency you have that can tell you about the problem in your area and what, if anything, you should do. In the meantime, you can look in the woods there and see how much the black cherry in your area is affected. --Spruce

I have no idea what black knot is but i'm sure that its best not to leave any pruning of plum trees till too late in the year as come fall when its much wetter(here in england anyway) there's a risk of fungal infection-can't remember the name of it now. I decided to prune our old plum tree heavily as it was old and badly needed some work. I just cut back all the branches leaving a skeleton to form a new crown. I'm not bothered about losing fruit as no one eats it and the garden gets covered in plums and the puppy eats them-not good!