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Rust Fungus Unleashed to Fight Exotic
Thistle By Jan
August 5, 2004
There's a showdown at the Mead Ranch in California's Napa Valley
this summer. In one corner is a biocontrol rust fungus; in the other, the
invasive weed yellow starthistle (YST).
Service and California Department of Food
and Agriculture (CDFA) scientists are refereeing the affair, but they're
far from being impartial. In fact, they're rooting for the rust fungus,
Puccinia jaceae var. solstitialis, whose spores they sprayed onto YST-infested
pasture at the Mead Ranch earlier this spring.
Since arriving in the United States from abroad in mid-1800s,
YST, Centaurea solstitialis, has elbowed aside native plants and established
itself as an invasive weed in many of the 48 contiguous states. California has
the largest infestation with 14-plus million acres.
According to ARS plant pathologist Bill Bruckart, the Mead Ranch
release marks the first U.S. field use of a fungus to biologically control YST.
Mowing, herbicide spraying and prescribed burning are some of the ways that
landowners now battle the invasive weed. The rust fungus is appealing because
it's self-spreading, host-specific and unrelenting once it becomes established
on YST populations, according to Bruckart, at the ARS
Foreign Disease-Weed Science
Research Unit at Frederick, Md.
Bruckart and CDFA collaborators Dale Woods and Mike Pitcairn
first released the fungus in July 2003 after obtaining federal, state and
regional approval. Since spraying the fungus' spores again this spring, the
team has been closely monitoring the ranch site's YST populations for disease
symptoms, such as orange-brown pustules on the thistle's stem and leaves. The
rust's unaided spread beyond the spray zone is also of interest.
The fungus, whose release caps 25 years of quarantined research,
joins five other previously released biological control organisms against YST.
These include two exotic flies and three weevils that diminish YST's
about the research in this month's issue of Agricultural Research magazine.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.