Sunburst Locust Tree Diseases

Powdery Mildew

• Powdery mildew appears on a honey locust and other hosts as patches of powdery white growth on leaves, buds and stems. Severely infected leaves may drop prematurely. The powdery mildew fungus does not require freestanding water to germinate and prefers temperatures between 60 and 80 degrees Fahrenheit and shady conditions. Control of powdery mildew on a "Sunburst" honey locust is only warranted if the tree is young and small and powdery mildew created a serious problem in previous years. Prune out heavily affected portions of the tree, only use slow-release fertilizers and selectively prune out dense growth on overhanging or adjacent trees to increase the amount of light reaching the honey locust leaves. Spray the tree thoroughly with a sulfur fungicide before the disease appears to prevent problems or apply horticultural oil once the white patches develop to treat it.

Cankers

• Honey locusts are prone to Thyronectria and other cankers. Foliage on branches where cankers develop turns yellow or brown and wilts. The canker itself generally appears as sunken, discolored tissue. A canker that develops over the circumference of an entire limb will cause the entire limb to die back. Where a canker develops on the trunk of the tree, it can girdle and kill the entire tree. Avoid accidental injury to the honey locust and provide the tree with deep, infrequent irrigation when rainfall is inadequate to minimize canker problems. Where cankers appear on limbs, remove the diseased portion by making a cut well below the bottom of the canker into healthy tissue. If the canker is located on the tree's trunk, there is no feasible treatment. Simply provide the "Sunburst" with excellent care to prolong its life.

Root Rot

• Multiple pathogens can cause root rot, root collar rot or other diseases such as annosus root disease. Infected trees decline and die. Conks may develop out of the root crown, depending on the causal pathogen. The bark on infected trees may separate easily from the wood, which may show streaking or discoloration. Prevent problems with root rot by avoiding accidental injury to the tree, overwatering and soil compaction. Remove affected trees or stumps promptly to minimize the potential for this disease to spread to other honey locusts or other trees in the landscape.

Wood Decay

• Various wood decay fungi, sometimes also known as sap or heart rots, can seriously affect a honey locust tree. These fungi destroy a tree's structural components, reducing wood strength and killing conductive tissue. Distinctive conks, brackets or other fruiting bodies develop near wounds or at the root crown and trees are particularly likely to lose limbs or fall when stressed by strong winds or heavy rain. Older trees are most prone to wood decay fungi. Prevent problems with these fungi by avoiding accidental injury to the tree and making all pruning cuts next to a branch collar -- the area of raised tissue where a branch meets a larger branch. Prune off dead or diseased limbs and consider removing the entire tree if it could injure people or property upon falling.