Fruit tree cancers, also called cankers, are pathogens that enter the tree through broken limbs and other wounds. Like human cancers, tree cancers are best dealt with at a very early stage. If a tree cancer has settled in the main crotch of the tree or has established itself on the main trunk, there may be nothing you can do to prevent the ultimate death of the tree. Tree cancers can be recognized as dark or watery areas that are sunken on a branch or the trunk of the tree. Often, gum or sap is protruding around the edges of the infection and the area often appears sooty. If you notice such symptoms on any of your fruit trees, swift and decisive action is required.
Inspect your trees thoroughly and mark all areas that appear diseased--sunken areas, black or sooty areas, areas that appear wet, and areas that are oozing sap or gum.
Fill a 5-gallon container with one-quarter bleach and three-quarters water. This will be used to sterilize your cutting equipment in the next steps so you do not spread the disease as you are trying to cut it away.
Remove all branches that have signs of cancer, cutting them off at least 4 inches below the infection. Dip your tools in the bleach solution before and after making cuts in order to keep the them fungus free.
Use the three-cut method for branches more than 1 1/2 inches thick: Make a cut halfway through the underside of the branch about 4 inches above the cancer, then cut straight down through the limb from the top side about 4 inches beyond your underside cut. As your top-side cut nears completion, the branch will break off at the point of your underside cut. This prevents the bark from stripping off down the tree and allows you to make a clean cut. Once the branch has fallen off, dip your cutting tools in the bleach and cut off the 8-inch stub with the cancer.
Use a sharp knife or saw to cut out any cancers growing on the trunk. Be sure to clean your tools frequently in the bleach solution and cut out the cancer until you have cut back to green, healthy wood.
Use a sharp knife or saw to cut out small cancers that have not infected an entire branch. Dip your tools in the bleach solution frequently to prevent the spread of the disease. Cut back all cancers to green, healthy wood.
Spray your trees with a copper sulfate solution (see Resources below) in the spring, just as the buds begin to show, and again in the fall when the leaves have fallen. This spraying will prevent the fungus from getting a foothold on your tree.