Have you noticed discolored areas or an orange ooze coming from the limbs or trunk of your tree? Cottonwood, birch, aspen, and other poplars, spruce, silver maple, apple, peach and cherry trees are highly susceptible to a fungus called Cytospora canker.
The orange ooze is the active reproductive part of the fungus called spores. These spores are dormant over the winter and become active during warm, rainy weather in the spring.
The cankers are sunken dead areas of bark with black, pinhead-sized pimples. The pimples are the reproductive structures of the fungus. Under moist conditions, masses of spores may ooze out of the pimples in long, coiled, orange, thread-like tendrils. Spruce trees have a canker that is orange in the middle and surrounded by a gray-hued, oozing area. This sunken area is surrounded by a swollen callus.
This disease most frequently invades areas of a tree that are under stress. Trees can be stressed by nearby construction that causes damage to roots, foliar diseases, drought, or general neglect. The cytospora enters through wounds caused by pruning, hail, staking or guying, and weed-trimmers. Cytospora can further weaken the tree, making it susceptible to attack from other plant pests. In time, the cytospora alone can kill the tree.
Cytospora can be prevented by correctly planting and caring for new trees, or planting resistant varieties. Trees that do not get cytospora include pine, juniper, ash, hackberry, linden and maple.
Once infection occurs, care should be taken to increase the tree's vigor. Good sanitation is also important. Remove and dispose of infected limbs, disinfecting tools after each cut.
Photos: Judy Sedbrook
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010