Disease Note

First Occurrence of Chrysanthemum White Rust Caused by Puccinia horiana on Florists’ Chrysanthemum in Oregon. J. A. Griesbach, Plant Division, Oregon Department of Agriculture, Salem 97310-0110. G. M. Milbrath, and T. W. Thomson. Plant Division, Oregon Department of Agriculture, Salem 97310-0110. Plant Dis. 75:431. Accepted for publication 12 December 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0431F.

Chrysanthemum white rust, caused by Puccinia horiana Henn., was detected 4 October 1990 on eight cultivars of florists' chrysanthemum (Chrysanthemum X morifolium Ramat.) in Portland, Oregon. The disease was found in a hobbyist's garden at a residential site in the metropolitan area. Light green to cream-colored lesions up to 4 mm in diameter were observed on the upper surface of infected leaves. The number of lesions per plant varied from two to several hundred. The teliospores (mean size 14.5 X 41.5 /µm) were hyaline to slightly yellow and two-celled, with a slight constriction at the septum. Telia were present in various stages of development, and some secondary spread to adjacent plants was observed. Because P. horiana is a regulated pest subject to federal postentry quarantine, the plants were destroyed. A survey of the plant material of the other 103 organized chrysanthemum hobbyists and associated clubs in Oregon failed to detect this disease. A delimitation survey of all 211 properties within 405 m (0.25 miles) also failed to detect any additional CWR. No CWR has been found in the 25 commercial nurseries that wholesale chrysanthemums in the state. Survey efforts will continue throughout the next growing season.