Jan 9, 2004

Chrysanthemum White Rust Found in Three StatesSource: The University of Florida

According to a recent report from the University of Florida, there is an outbreak of Chrysanthemum White Rust found in New Jersey, New York and California.

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Within the last 25 years the pathogen, caused by the fungal pathogen Puccinia horiana, has come into the United States from infected plant material. The disease causes conspicuous and debilitating lesions on all of the green above-ground parts of florist chrysanthemum and some close relatives. The symptoms appear mostly on the leaves as light yellow chlorotic spots on the upper leaf surface while corresponding buff-white raised pustules appear eventually on the lower leaf surface. There are only two spore stages in this rust’s life cycle.

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The telial stage spores are present in the large unsightly protuberant lesions on the leaf underside. These teliospores germinate in place under very high humidity to produce the other airborne or water-splashed spore stage, basidiospores. These basidiospores die when they dry out, so very moist conditions cause chrysanthemum white rust to spread. Basidiospore production from teliospores can occur in as little as three hours after wetness, and two hours of leaf wetness is all that is required for successful infection by dispersed basidiospores. New telial pustules appear in about two to four weeks after infection.

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The USDA-APHIS-PPQ policy is to eradicate white rust upon detection. Conscientious survey over several weeks, careful destruction of infected and exposed plants when discovered, and application of appropriate fungicides to nearby plants on a prescribed schedule can very successfully eradicate the disease.