Puccinia jaceae var. solstitialis 
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Common Name
Yellow starthistle rust
Weed Impacted
This fungus attacks yellow starthistle. Fungal spores interfere with normal plant growth and and may reduce plant vigor.
Agent Description/Field Identification
The most conspicuous stage of fungal growth is the urediniospore, which occur in clusters and appear as rust-colored pustules or spots on the leaves and stems.
Life Cycle
The life cycles of rust fungi are complex and typically involve several stages of spore development. P. jaceae var. solstitialis has five spore stages. The spores are dispersed by wind and germinate when temperature and moisture levels are ideal. Urediniospores are the primary infective stage and are present throughout most of the plant’s life.
Availability
Field trials are still in progress, but the rust is available on a limited basis. To inquire about availability and to request this biocontrol agent, please download, complete and submit this form.
Comments
Adequate moisture levels (long, cool dew periods) are necessary for the fungus to establish successfully.
Using the Agent: Integrated Weed Management (IWM)
Rust fungi like P. jaceae var. solstitialis can typically be used in combination with other biological control agents.
New releases of P. jaceae var. solstitialis should only be made where weed infestations are large and immediate eradication is not the primary objective. Individual plants and smaller, satellite populations can either be hand-pulled or sprayed; although studies have shown that yellow starthistle can develop resistance to some herbicides. Consult with your county weed office, Extension office or an IWM practitioner to determine which herbicide treatments are safe and appropriate.
Any management of yellow starthistle should involve revegetation with native or other desirable plants, especially grasses. Competition between plants stresses weeds and can allow for more effective treatment. To learn more about revegetation and IWM, click here.
References
Coombs, E. M., J. K. Clark, G. L. Piper, and A. F. Cofrancesco, Jr. 2004. Biological Control of Invasive Plants in the United States. Western Society of Weed Science, Oregon State Univ. Press, Corvallis.
Gibbs, L.A., M.W. Murray, T.M. Sterling, and N.K. Lownds. 1995. Comparison of picloram-resistant and -susceptible yellow starthistle in a replacement series. Proceedings, Western Society of Weed Science 48:26.
Sterling, T.M., N. K. Lownds, E.P. Fuerst, T.S. Prather, and R.H. Callihan. 1991. Potential mechanism of picloram resistance in yellow starthistle (Centaurea solstitalis L.). Weed Science Society of America Abstracts 31:80.
Photo Credit
Puccinia jaceae var. stostitialis - USDA archive photo, USDA Agricultural Research Service http://www.ars.usda.gov/is/graphics/photos/aug04/k11320-3.htm
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