Brown Discharge From a Cottonwood Tree

Disease Identification

• Cottonwood tree is susceptible to the cytospora canker disease caused by members of the cytospora fungal group. The pathogen has a number of other host trees including aspen, birch, apple, peach, elm and willow. The disease is also common on woody shrubs. The causal agent in cottonwood trees is Cytospora chrysosperma or Valsa sordida.

Symptoms

• The disease is characterized by the appearance of slightly sunken, brown areas on the branch and trunk bark. These lesions are irregularly shaped or circular. As the lesions or canker expand, the entire stem or branch is girdled and eventually killed. Smaller twigs die without the presence of cankers. The wood under the canker smells foul and turns black and water soaked. A brown-colored liquid or gum-like substance starts to ooze from the affected sites. Dead bark areas either fall off or remain attached to tree.

Favorable Conditions

• Cytospora frequently invades weak, stressed trees or the specific tree areas that may be damaged or wounded. The fungus is most active during the warm-weather periods in spring and between fall and winter. Affected trees are usually dormant during this period and less able to defend themselves. Other causes that increase susceptibility include stress from drought, spring frost or sunscald.

Control

• Keeping trees in vigorous health, minimizing chances of environmental stress and avoiding unnecessary wounding and damage are among the primary defense strategies against cytospora infection. Fertilize trees before winter and summer and control pest infestations before they get a chance to weaken trees. Use resistant-tree varieties. Prune out and remove all affected smaller branches and limbs. Carve out and remove cankers from larger branches and trunks before they can spread. There are no chemical-control options for the disease.