Question
Hi I have these knots all over the branches on my plum tree at this time he tree is full of fruit so I haven't cut the branches off can I eat the fruit on the tree and when should I cut the branches off to try and save my tree and what products can I purchase to stop the knots from coming back or is my tree doomed?

Answer
If the knots are confined to the branches, you will want to prune the knots off 4-6 inches below the knots.  The knotted areas are releasing spores which can blow to other trees and infect new branches on your tree.  Usually, the knots will eventually girdle the branch and kill the branch above the knot.  You should disinfect pruning tools between each cut by dipping in a bleach solution (1 part household bleach and 9 parts water).  Removed wood should be disposed of in the trash or buried.  If the knot has reached the trunk, it may be possible to chip away the knot, but this may further damage the tree.  

You can use a product such as Monterey's Fruit Tree, Vegetable and Ornamental Fungicide or Captan Fungicide for Fruit & Ornamental Trees.  Other products may be available at your local garden center.  You can verify by checking the label to see if it is labeled for black knot on cherry.  Be sure to follow the directions for mixing rate and proper timing.  The fungicide will not cure the tree and make the knots go away.  It's purpose is to prevent new infections on the branches and trunk.

There is no problem with eating the fruit off the tree.  The disease does not pose any problems for humans, just plums and cherries.  You can wait until after the fruit has ripened to prune out the knots  During this period, it is best to avoid overhead watering since it can spread the spores.  Use drip irrigation and avoid wetting the foliage if possible.   

If you live in an area where other cherries and plums may be present in the woods, you may want to scout them out.  If you control the disease on your tree, additional spores may be blowing in from infected trees in the area.  You may be able to cut infected branches off these trees or cut the trees down to help prevent new infections.

Good luck!