Green ash is an oddly shaped tree while growing up, according to the US Department of Agriculture, that becomes a lovely oval as it matures. The ash is common throughout the United States, and so are its many pests and diseases. Pests and disease destroy the glossy green of the leaves and sometimes kill the tree outright.
Anthracnose is the most common fungal infection of green ash, according to North Dakota University Extension. Ash Anthracnose is caused by a fungus called Gnomoniella fraxini, infecting buds and leaves of the tree. The buds develop necrosis and fall off early, while leaves wilt. New shoots often die off altogether. Control of Gnomoniella fraxini requires burning of dead material, removal of diseased limbs and the spraying of pesticide.
Fomes fraxinophilus, Polyporus sulfureus and Phellinus punctatus cause a condition called heart rot in green ash tree, according to North Dakota University Extension. Heart rot destroys the green ash tree from the inside out, causing structural defects in the wood. Often the tree needs to be removed.
Borers are a common pest in green ash, especially the ash borer, lilac borer and carpenterworm, according to the USDA. The ash borer lives at the base of the tree trunk and causes die back of the entire tree. Lilac borer causes swelling in the trunk. Carpenterworm digs through the tree, often pushing out sawdust from inside the tree. Large infestation of carpenterworm causes the tree to wilt and weakens the structure.