Ash rust is an easy disease to diagnose. The causal rust fungus, Puccinia sparganioides, produces bright yellow-orange spores on infected leaves, petioles, or stems. Diseased tissues are also often swollen and distorted.
The spores produced on ash infect marsh and cord grasses, the alternate hosts of this rust fungus. The fungus overwinters on these grasses.
The disease is rarely destructive enough to warrant control measures. Severe rust in successive years can weaken trees, especially young trees, and make them more susceptible to winter injury.
This article originally appeared in the June 23, 1995 issue, p. 92.