Question:
What are the orange-colored growths on the leaves of my ash tree? Is control necessary?Answer:
Ash rust is probably responsible for the orange growths on your ash tree. Ash rust is caused by the fungus Puccinia sparganioides. The fungus produces conspicuous swellings on leaves, petioles, and twigs. Infected leaves, petioles, and twigs may become twisted and distorted. Infected areas eventually produce masses of yellow to orange, powdery spores.
Puccinia sparganioides requires 2 different plant hosts to complete its life cycle. Part of its life cycle is spent on ash and the remainder on cordgrass (Spartina spp.). The spores produced on ash are carried by the wind to cordgrass. The fungus then infects the cordgrass. In spring, spores from infected grasses are blown by the wind to nearby ash trees. Warm, wet weather in spring favors ash infections.
Ash rust does not seriously harm healthy, well established trees. Control measures are usually not necessary.