Diseases of onion and garlic (
Garlic rust
Garlic rust is caused by the fungus Puccinia allii, also called Puccinia porri. Early symptoms are small white to yellow spots or flecks on leaves that turn yellow to orange as different stages of the fungus develop in the leaf tissue (photo 1). The yellow to orange spots become pustules called uredinia that contain urediniospores (photo 2). Urediniospores are the repeating stage of the fungus, that is, they infect the garlic leaves in the same season (photo 3). They are disseminated by wind and spread long distances. Later the pustules turn black (photo 4) as they develop into telia containing dark colored teliospores (photo 5). Both urediniospores and teliospores probably survive for long periods of time and are sources of inoculum for infections of successive crops.
Leaves may become so heavily infected that they appear almost orange in color. Severely infected plants die. Other Allium species are probably hosts, and in trials in California, http://vric.ucdavis.edu/veginfo/commodity/garlic/garlicrust.html , onion and chives were infected. No infections of commercial onion have been reported in Arizona.
No resistant varieties of garlic are known. Preventive applications of a foliar fungicide are critical for disease control.
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February 10, 2003