Spring 2010 Field Observations
by Steve Tjosvold
A new disease was recently discovered in Santa Cruz County -- gladiolus rust (GR), a disease that appears as orange pustules on the leaves and stems of its host. This rust mainly infects Gladiolus, but has been known to infect other members of the Iridaceae: Anomatheca, Crocosmia, Melasphaerula, Tritonia and Watsonia. It is found in Mexico and parts of Africa, Australia, Brazil, Europe and Martinique; in the United States, it has been detected in Florida and California (Alameda, Contra Costa, Marin, San Diego, San Francisco, San Mateo and Santa Clara counties).
The fungus that causes the disease, Uromyces transversalis, is spread by wind and movement of infected plant material. Spores can contaminate corms, but they do not infect the corms directly. There is some evidence that spores may be produced from cut flowers under favorable field conditions. While rust diseases have the potential to cause significant damage, they can be managed by early detection and timely fungicide applications. Frequent scouting for signs of rust is important for early detection. However, under the current management and eradication plan for GR, all host plants would have to be destroyed if the pathogen were to be detected in a commercial nursery.
Images and more information on this disease can be found in the USDA report, “The Gladiolus Rust (Uromyces transversalis): A National Management Plan for Exclusion and Eradication”.
For a discussion on the situation in San Mateo County, see Colleen Warfield’s “Regional Report,” in the 2009 Winter/Spring issue of CORF News.