Proper Pruning to Fight Decay

By: Anthony C. Arnoldi, Certified Arborist

Winter 2003 Newsletter in Adobe PDF format Proper pruning can minimize and/or mitigate the effects of decay in your trees.

No, this isn’t an advertisement for toothpaste, but the presence of decay and its advancement throughout a tree is of paramount importance. This article will show how decay impacts a tree and what proper pruning can do to minimize and mitigate its effects.

Decay (rot) of wood is caused by several different fungi. We have all seen or heard of trees that were so rotten (decayed) that they became dangerous or were failing in health due to advanced fungal attack. How did they get that way? It usually starts in a small way and gains momentum over time. When branches die, decay fungi immediately colonize them (from spores ever-present in the air) and begin to feed on the broken-down cellulose they create. As they feed, growth of fungal strands spreads out in the branch, slowly digesting ever more wood and resulting in more and more fungus growth. When there are many dead branches, this effect is multiplied many times over.

Trees try to limit spread into the main trunk by forming defense barriers within the wood. A main defense barrier opportunity for a tree occurs where the branch meets the trunk wood. This is the branch collar, the structure where the primary defense happens. If the tree is healthy and has sufficient reserve energy, it will create a barrier from defense chemicals that block fungi from crossing this line and entering the trunk wood. If the tree is weak or the fungus has a large dead branch to feed on, it may overcome this barrier and enter the trunk. If many dead branches are in the tree and the barriers are breached, the resulting decay of fungus-colonized wood will spread and coalesce, overwhelming the trunk and spreading ever downward. Once in the trunk, the tree attempts to “wall off” or compartmentalize the fungus, but food storage area is lost as a result. Maintaining defense chemical walls all along this containment area is “expensive” for the tree and can exhaust all its resources.

Enter professional Arborists. They can recognize and remove much of the infection early in this progression by cutting out infected branches without injuring the branch collar or breaching the chemical defense barriers. Careless pruning adds to the tree’s burden, but proper pruning can remove much of the infection from the tree and prevent it from having to use up its resources. Many jobs passed off as “trimming” by unschooled “arborists” actually make matters worse and cause stress and advancement of decay in trees.

Don’t let this happen to your trees! Call your Wachtel Certified Arborist for skilled expertise in this matter to help greatly extend the life and health of your valuable trees.

© Copyright 2003 – Wachtel Tree Science & Service, Inc.

Return to Newsletters


Request a Consultant

Interested in having one of our qualified staff contact you about your trees and landscaping? Let us know your ZIP code and we'll let you know who's in your area.

Request a Municipal Specialist

Specialized Services:

  • Urban Forest Management
  • Tree Preservation Planning Involving Wooded Sites
  • Corporate Campus Tree Mapping & Assessment

Click to Contact


  • Robert & Dorothy Miller - Mequon

    " Tree removal was recommended, we had a contract, the job was completed on Tuesday. We are very pleased, excellent team work. Thank you to Anthony."

  • John K. - Waukesha

    "Always pleased with how you keep our trees happy and healthy!  Thanks!"

Winter tree care and pruning newsletter

Seasonal Tree Care Newsletter

Read More

International Society of Arboriculture The Tree Care Industry Association Wisconsin Arborist Association TCIA Member


of tree care