Pruning Out Dead Or Diseased Wood
In order to avoid insect and fungal problems, it is important to regularly prune out wood that is dead. Diseases and insects are attracted to dead branches on trees and shrubs, and once they have been established there, they will spread into live and healthy wood. If allowed to remain, these pests will weaken the tree, allowing other insects and disease to become established. Eventually the tree will die of one or many of these causes.
It is important to use tools that are sharp, as dull tools will make an uneven cut which will lead to tissue at the site of the cut dying, leaving it open to infection.
It is also important to use tools that are sterilized, since fungi can very quickly colonize dead wood, even though it may not appear to be infected, it is very likely to be. Fungi are easily spread by contact, so dipping your tools in a sterilizing solution between every cut will prevent the possible spread of disease. We recommend a mixture of one part Bleach or Javex to nine parts water.
When pruning out dead wood as well as diseased wood, it is important that the cut be made four to six inches into live and healthy looking wood. This will ensure that all dead and dying wood is removed. If the cut is made too close to the infected wood, or dying wood, then the problem will likely reoccur. To find the point where the dead wood ends and the live wood begins; move back along the branch making nicks in the bark until the wood is green. If the bark has no green inside, then the wood is dead.
When pruning a branch or twig, it is important to cut correctly. In the case of pruning smaller twigs and branches, always move back along the wood to the nearest bud or branch. The cut should be made not more than ¼ inch from the bud, as cuts too far away cause dieback. Anything too close will damage the bud, or allow disease spores to enter it. Slant the cut away from the bud or branch, to prevent water from accumulating on the bud.
When pruning out large branches, more than one cut is needed. First, make a partial cut on the bottom of the branch a few inches away from the branches origin. Next, make a second cut on the top of the branch a few inches beyond your first cut, this second cut should be complete, allowing the branch to fall. The undercut that was made will prevent the bark from stripping beyond that point. Around the base of the branch, where it joins the trunk of the tree, or the main branch, there is a ring of tissue made up of the branch collar and the branch bark ridge. The cut should be made outside of this ring. If the bark ring and the branch collar are cut, the wound will close more slowly, and if the cut is too far away from this ring, a stump is left and this tissue usually dies. Now you may make the final cut, which should be close to the trunk, but not into the branch collar.
By Dr. Bill Paton and Laura Tilley