Greenhouse and Nursery - Don't Mistake Chrysanthemum Rusts

The following is information on white rust vs. brown rust on chrysanthemum from the UD plant disease diagnostic lab.

There have been some questions about another rust on chrysanthemum caused by Puccinia tanaceti, brown rust. This occurs in the U.S., but is easily distinguished from white rust caused by Puccinia horiana. The pustules are dark rusty to chocolate brown and occur on both surfaces of the leaves. Microscopically, the spores of brown rust are round urediniospores, very different from the teliospores of white rust. What we have seen in the past day or two is some darkening with age of the pustules of white rust to a buff or tan color.

Please do not hesitate to send in samples for confirmation,

Nancy F. Gregory, Plant Diagnostician, Department of Plant & Soil Sciences, University of Delaware