Spread of disease and decay

Disease

One common problem with tree care is that so many people are unaware of the spread of bacterial, fungal and viral infections passed on through pruning tools. There is something we can do about this.  

Tools should be clean and sanitized as well as sharp. Although sanitizing tools may be inconvenient and seldom practiced, doing so may prevent the spread of disease from infected to healthy trees on contaminated tools. Tools become contaminated when they come into contact with fungi, bacteria, viruses and other micro organisms that cause disease in trees. Most pathogens need some way of entering the tree to cause disease, and fresh wounds are perfect places for infections to begin. Micro organisms on tool surfaces are easily introduced into susceptible trees when subsequent cuts are made. The need for sanitizing tools can be greatly reduced by pruning during the dormant season.

If sanitizing is necessary it should be practiced as follows: Before each branch is cut, sanitize pruning tools with either 70% denatured alcohol, or with liquid household bleach diluted 1 to 9 with water (1 part bleach, 9 parts water). Tools should be immersed in the solution, preferably for 1-2 minutes, and wood particles should be wiped from all cutting surfaces. Bleach is corrosive to metal surfaces, so tools should be thoroughly cleaned with soap and water after each use.  

Damage & Decay
Tree wounds are the first step in a process that may lead to discoloration and ultimately to decay of tree trunks, roots and limbs. Broken branches, pruning stubs and mechanical injuries to roots, trunk or branches are the types of wounds most commonly associated with decay problems. One of the most frequent causes of damage to trees in the landscape comes from lawn equipment. Mowers and string trimmers can damage the bark at the base of the trunk.

Initially there may be no visible evidence of injury, although the injured plant will lack vigour. Continued injury will result in visible wounds at the base of the trunk. Besides restricting the movement of food, water and mineral elements, these wounds become excellent points of entry for insects and wood decay fungi. When an injury or break in the bark exposes the underlying wood, bacteria and fungi in the air and on the bark contaminate the wound surface. At the same time, the tree responds to the wound by producing chemical and physical barriers in an attempt to block the invasion of micro organisms and to seal off the damaged area. Organisms which are able to overcome these protective barriers can then colonize and invade the wounded tissues. Among these organisms are the wood decay fungi. Not all wounds result in extensive decay since trees are frequently able to successfully “compartmentalize” or “wall-off” the decayed area. In many cases, the formation of internal barriers to fungal movement and infection can prevent the decay fungi from spreading. The ability of a tree to internally compartmentalize decay differs from one individual tree to another.  

There are no controls or cures once wood decay has begun. Decaying trees or branches should be removed when they become potentially hazardous.