CANKERS - A large number of fungi cause cankers which result in branch dieback. Cankers are more common on stressed trees planted in poor sites and in poorly maintained trees.Young cankers are slightly darker in color than adjacent healthy bark and appear slightly sunken. As cankers enlarge, they kill the living woody tissue within the branch or trunk. Canker growth may cause the bark along the edges of the wound to crack and fall away, exposing the dead wood underneath. After a canker enlarges enough to cut off a tree's water and nutrient supply, the portion beyond the canker dies.  Because of a twig's smaller girth, twigs are killed more quickly than larger branches. Symptoms may include progressive upper branch dieback, disfigured branch growth, or target shaped areas on trunks with concentric rings of dead bark. At Morris Arboretum, one of our redbud trees located by the Log Cabin has many cankers on its branches. Some of these cankers don't seem to be affecting the tree, yet.  However, this summer some of the branches have died and been removed due to cankers preventing nutrient flow to the canopy beyond the canker.  The image shows one of the redbud's sunken cankers.There are no chemical controls for cankers and they cannot be stopped once they become extensive. The only control measures are to remove affected branches and prune back to healthy wood (see drought). Stressed trees should be fertilized and watered during drought to promote better tree vigor.