Anthracnose (fungus – Gloeosporium sp.): Large areas of the leaf, especially along the edges and veins, turn brown. Premature defoliation will follow severe anthracnose infection during wet seasons. The disease may be confused with problems caused by weather adversities or other physiological problems. Spraying with a fungicide two or three times at 14 day intervals during humid periods will control the disease.
Leaf Spots (fungi – Cylindrosporium sp., Marssonina sp.): Among the most common foliage diseases of ash that occur virtually wherever ash is grown. Lesions appear early, hundreds may develop on a single leaflet. They are very small at first. Spray as recommended for anthracnose to control the disease.
(fungi – Mycosphaerella fraxinicola, Phyllosticta sp.): Another common leaf spot of ash appears toward the end of summer. Groups of small dark fruiting structures form in spots on the bottom of the leaf, while the upper side may show only a slight spotty discoloration. By the time the spots on the top turn brown, defoliation has begun. Spray as recommended for anthracnose to control the disease.
(fungi – Cercospora fraxinites): Spots are irregular to almost circular, three to seven mm in width. The long, thin, many-celled spores are produced on black stromata within the dull gray-brown spots. Spray as recommended for anthracnose.
Rust (fungus – Puccinia sparganioides): Swollen and distorted gall-like structures occur on leaves and twigs. The orange swellings are more common early in the growing season, particularly in the Gulf Coast area. Two stages of the rust fungus are known: one which occurs on ash trees, the other on grasses, Spartina sp. Spraying with fungicides at two to three week intervals during early spring will control the disease.
Cotton Root Rot (fungus – Phymatotrichum omnivorum): Ash is moderately susceptible to the cotton root rot fungus, particularly during the younger stages of growth. (See section on Cotton Root Rot)
Wood Rots (fungi – Poria sp., Fomes sp., Polyporus sp., etc.): Most of these fungi attack only weakened or wounded trees. Infection usually takes place through wounds caused by lawn mowers, pruning, or strong winds. Trees decline slowly for no apparent reason and the fungus slowly rots the wood. After the disease has progressed for some time, leathery, hard structures (conks) can be seen attached to the lower parts of the trunk. These are fruiting bodies of the fungus appearing as bracket growth during certain times of the year. Control is accomplished by avoiding mechanical wounds, treating exposed wounds with pruning paint, fertilizing trees as needed and protecting from insects.
Powdery Mildew (fungus – Phyllactinia guttata): White powdery fungus growth on the leaves during the summer, then forming small black round fruiting structures in the late summer and fall. Damage is usually not extensive enough to warrant control.
Hairy Root (bacterium – Agrobacterium rhizogenes): A large number of very small roots develop either from the base of the stem or the larger roots. No control is known.
Cankers (fungi – Cytospora sp., Diplodia sp., Dothiorella sp., Nectria sp.): Several fungi cause branch and trunk cankers on ash. None of them are very common. Prune out infected branches. Maintain the trees in good condition by fertilizing, watering and spraying for insects.
Leaf Scorch (physiological): (See section on Leaf Scorch)