Cytospora Canker

The cool wet weather we have been experiencing encouraged a number of tree diseases, including cytospora canker of spruce trees. Cytospora canker is a fungus that primarily attacks blue and Norway spruce, although Siberian and white spruce may be attacked as well.

Cytospora is a stress-induced disease, meaning that it only attacks trees that have been weakened through physical injury, having too much or too little water, overcrowding of trees or other factors that weaken the tree. The Cytospora canker enters wounds on the tree and slowly spreads from the bottom of the tree upwards. Symptoms of cytospora attack include browning or purpling of needles then the gradual death of twigs or branches.

Looking at the underside of the affected branches, one can see white, dried up resin and pitch near the site of the canker; however, the actual canker is not easy to see unless you scrape bark away from the wound. The sapwood of diseased branches often is a blue to brownish color. Cytospora canker spores will persist on a tree for a number of years gradually enlarging and spreading, causing twigs then whole branches to die.

This damage typically starts at the ground and works its way to the top of the tree. The damage is mostly cosmetic in the beginning but prolonged attack can result in the gradual death of the tree. Cytospora can attack trees damaged by weed whackers, mowers, or other mechanical means. Another factor that encourages attack is planting trees too close together causing limited air flow and damp conditions. Insect or bird damage, soil compaction, and over-watering also encourage the spread of the cytospora fungus. Spruce trees can also become weakened by drought.

Control of the disease entails pruning out infected branches so that the fungus can not spread to healthy braches. The tools that you use to remove these braches should be treated with alcohol to destroy any cytospora that might be present before you use them on another tree. Some experts encourage fertilizing weakened spruce to boost their vigor but most mention that there is no fungicide that will cure the disease.

The best way to avert this disease is to plant spruce trees in deep, well drained soils, avoid injury and provide trees with what they need to stay healthy. Planting less susceptible species or cultivars is another way of preventing the disease.

Article by FCFCDB

Nature Notes for 9/8/2013