Birch trees vulnerable to killer diseases

The numbers of living, healthy birch trees have been rapidly declining in Central Alberta.

The numbers of living, healthy birch trees have been rapidly declining in Central Alberta.

It is a common sight to see birch trees with dead tops or branches. In extreme cases the entire tree will be dead.

Birch trees, weeping and paper, are large majestic trees commonly found in Alberta yards. They are noted for their attractive white bark, small green leaves and yellow fall colours.

Birch trees are usually used as a specimen, or a shade tree. In the wild they are one of many trees, shrubs and herbaceous plants that form a thicket or bush. Plants within this ecosystem compete for moisture while at the same time shading and protect the birch tree’s shallow roots from the heat. A lawn does not offer the birch trees the same protection. In fact, it is part of the problem as lawns requires more moisture than the native undergrowth. During hot dry periods, the birch roots become too warm and dry. As a result the trees become stressed.

Stressed trees react by producing more sap than usual, making the tree more inviting for diseases such as perennial canker. This disease is caused by a fungus named cytospora which enters trees through small openings in the bark. Once the fungus enters a tree, it forms a canker that chokes the phloem and xylem cells, expanding until it slowly girdles the branch. The process can be very quick and kill the tree in a season or it can take a number of years. Unless one looks for dead branches on a regular basis, the first sign is often a section of tree not leafing out in the spring.

Checking for perennial canker, cytospora, is as simple as removing a small piece of raised bark or canker. The tell tale signs are small pimple like structures which contain black fungus. Like most diseases the fungus will leave the host and travel infecting other plants.

The ideal conditions for this to occur are warm, moist spring days that allow the fungus to catch the wet breeze and transfer to another susceptible plant. A chemical control is not available. At present, good cultural practices are the best way to control the disease. A healthy tree will not be subject to an infection.

Fertilize birch trees in the spring to ensure the plant has adequate nutrients. Moisture is also very important. Make sure the tree receives adequate moisture during spring and early summer.

The tree should also receive extra water just before the ground freezes in the fall. Placing a sprinkler under the tree to ensure the roots are moist and cool in hot weather will help reduce the tree’s stress.

Remove dead and diseased wood cutting back to a branch or limb with healthy wood.

Prune in dry weather as the fungus spreads when it is wet. Burn or double bag all diseased wood immediately. Do not keep it for firewood or take it camping. Do not leave the dead tree standing as it will enable the disease to spread. Action needs to be taken to stop the spread of Perennial Canker before it kills more birch tree.

To ensure that trees are not stressed making them susceptible to insect and diseases they must receive an adequate amount of sunlight, moisture and nutrients.

Linda Tomlinson is a horticulturalist and educator living in Rocky Mountain House. You can contact her at your_garden@hotmail.com.

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