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Eradicating Cytospora Canker
- During bloom or later, remove all cankers on small branches, cutting at least 4 inches below the margin of the canker.
- Surgically removing cankers on younger trees can prevent the slow decline and ultimate death of the tree. Recent research trials have shown that although this procedure is time consuming (the average treatment time ranges from 1 to 5 minutes per canker), it is nearly 100 percent effective. If the surgery is done improperly, however, the canker is almost never eradicated. When surgery is conducted before too many cankers are evident on each tree, cankers can be eliminated from young orchards before extensive infection and tree death occur.
The best time of the year for canker surgery is May and June. To remove diseased tissue and promote maximum healing, take the following steps (Figure 5.6 below):
1. Do not attempt surgery on cankers encompassing more than half the branch circumference. Diseased tissue often extends beyond the canker margin that is visible at the bark surface.
2. Place your knife at the top of the canker 1/2 to 1 inch above visible diseased tissue.
3. Outline the area to be removed, maintaining a 1/2- to 1-inch margin beyond the canker. Outline a point at the top and at the bottom of the area to be removed. When outlining, press the knife blade straight through the bark into the wood.
4. Push the knife blade beneath the bark of the outlined area and remove the diseased tissue. It is not necessary to dig into the hardwood.
5. Clean out all diseased tissue. Note: If the diseased brown tissue extends into the margin of the cut, expand the margin until only healthy (green) tissue is evident at the margin. Keep the margin of the cut clean; torn tissue will not heal properly.
6. Do not paint cut surfaces with standard wound dressings (water asphalt emulsions, oil-based paints, or Latex paints). They have not proven beneficial in the wound-healing process.