The Arizona ash tree (Fraxinus velutina) is commonly called the velvet ash and can reach 50 feet in height. The tree often thrives in less then ideal situations such as drought, urban pollution and poor draining soil. When the Arizona ash reaches a large size, severe breakage is common because multiple trunks often form on the tree which weaken the tree's base and cause a split to occur. To prevent this serious condition, early pruning during the tree's first 15 years of life is important. Unfortunately, the tree is also susceptible to pest borers which further weaken the wood and can cause the tree's untimely death.
Rake all leaves and twigs up under the Arizona ash tree regularly. Remove all leave in the wintertime from the areas around the tree. The Arizona ash is highly susceptible to anthracnose, which is a fungal disease that affects the leaves of the tree and causes it to quickly loose foliage. Anthracnose will not kill the tree but it causes it to look unsightly. Control the fungus by removing all the dead leaves that the fungus can flourish in.
Fertilize the Arizona ash in the spring, summer and fall using a 12-12-12 fertilizer. Follow the directions on the label for application.
Prune the Arizona ash tree in late February. Remove all branches that cross each other. Cut away all dead or damaged branches. Prune enough limbs to allow light to reach the middle of the tree and the air to flow freely. Airflow can prevent fungal infections in the tree. Removal of a large amount of unnecessary branches every year will prevent the Arizona ash tree from breaking when fully grown.
Maintain the Arizona ash tree's health by providing regular water and fertilizer to prevent borer pest infestations. Borers normally attack trees that have been weakened from lack of water or nutrients. Damaged branches with borer infestation need to be promptly removed from the tree. Even with removal of the infected branches the outlook for an Arizona ash infected with borers is grim. Spray the tree during adult borer activity with the insecticide permethrin. Apply the systemic insecticide imidacloprid around the base of the tree. Follow the directions on the label for the application of both insecticides.