A stress-related disease of trees and shrubs that causes decay of the bark and wood. Cankers have to start with a wound through the bark. Healthy soil and plants are the best solution. Use Tree Trunk Goop on the injured spots, improve the environmental conditions and apply the Sick Tree Treatment. Synthetic fungicides do not work on this disease. Hypoxolyn canker is a common disease of certain oaks such as stressed post oaks, especially after droughts or long rainy seasons. The brown spores rub off easily and the bark sloughs off the trunks. No treatment is necessary other than improving the immune system of the tree. This is the #1 disease seen on post oaks. The stress leading to this disease is often caused by herbicide treatment to the root zone or the trees being too deep in the soil. Look for cracks, sunken areas, or raised areas of dead or abnormal tissue on woody stems. Cankers ooze sometimes. Cankers can girdle shoots or trunks, causing the plant above the canker to wilt and die. Blights and canker diebacks look quite similar. Cold-injury symptoms can look like or lead to the development of cankers.