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Ash Leaf Rust Description:

Ash leaf rust can be a significant problem in the Mid-Atlantic area and along the New England coast. Leaves, petioles, and green twigs become infected during May and June. When the infection is severe, premature defoliation can occur.

Hosts:

In spring, rust spores appear on ash leaves as bright orange or yellow powdery masses. They move inland from marshes and infect newly emerging leaves of ash trees.

Biology and Symptoms:

This fungus is rarely destructive, although it has been reported to kill very young trees. Premature defoliation can occur with severe infections. If trees are infected with ash leaf rust for several consecutive years, trees can become weakened and are more susceptible to winter damage and branch dieback.

Management:

Maintaining the overall health of your trees is important, infected or not, including:

  • Deep root water during periods of drought  

  • Fertilize with ArborGreen Pro®

  • Mulch to moderate soil moisture loss and soil temperature

Preventative fungicide sprays are available, but speak with your professionally trained arborist about which option works best for your needs. Applications made after the infection has occurred will not be effective. If practical, eliminating alternate hosts, such as marsh grass and cord grass, can be effective also.

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