tree cankers
A canker is defined as a diseased, sunken lesion on woody tissue. There are three types of cankers; fungal, bacteria or frost.
Frost cankers, actually physiological disorders, are cracks on the bark caused by freezing and thawing. Fungal and bacterial pathogens usually gain entry through frost cracks, pruning wounds, wind damage, or sun scald. Sunscald is another physiological condition that occurs on the south west side of tree trunks exposed to bright winter sunlight, most often affecting May Day trees. Fungi are in fact microscopic plants, which do not invade healthy plant tissue. Once inside the plant the fungi move into the sap system and eventually decrease or stop water from moving upward from the roots to the branches. If you look closely at the trunk where the branch is attached, you may see cracks in the bark with the bark peeled back from the crack; elongated oval, sunken or darkened areas in the bark or places where sap is oozing from broken areas in the bark.
One common fungus causes Cytospora canker in Cotoneasters, particularly inside older hedges where there is little light or air circulation; a perfect place for fungi to grow. The commonly observed orange Nectria canker on Cotoneaster is actually a secondary rot organism that does not harm the plants itself. Some of these cankers are incorrectly diagnosed as fireblight, in which the leaves die because the bacteria kill them, and then the cankers come afterwards.
While possible on most trees, fungal Cytospora cankers are most prevalent on Mountain-Ash, Poplar, Spruce, and Willow. Bacterial cankers, also called Slime Flux or Wetwood, are most frequently observed on Poplar trees. There is no chemical control for fungal or bacterial cankers. The only way to control them is to prune the branches back well into healthy wood. In the case of hedges; remove the inside; affected branches and then the remaining branches will grow into the centre because of the available light and air circulation. This is not a cure as the fungi or bacteria could spread within the sap of the plant and cause more cankers. Eventually, if it invades the main trunk, the tree may have to be removed.
Be careful to clean pruning tools with a 10% bleach solution between each cut, as fungi or bacteria spread on tools. It is difficult to diagnose cankers by describing them on the phone so bring in a branch to our staff for easier identification.