The following is information on ash rust, a disease now present in the landscape.
Ash rust caused by the fungus, Puccinia sparganoides, was observed last week on white ash. This rust produces bright orange swellings on the green stems and petioles; infected leaves are distorted and have numerous orange crown-shaped pustules. The infections are few at present but it can be pretty spectacular when leaves stay wet for long periods of time (6-8 hrs). In 2006, ash rust was everywhere. It is too late for any chemical control. The alternative host for this rust is Spartina spp. (marsh and cord grasses). Most of the real damage is to nursery trees that lose the new green twig growth. If symptoms are not present, preventative fungicide applications of labeled fungicides for rust are advised for nursery growers. Myclobutanil (Systhane or Immunox for homeowners) is the only fungicide registered for this disease.
Ash rust. Photo from the Iowa State University Plant Disease Clinic.
Information from Bob Mulrooney, Extension Plant Pathologist, UD.