Posts Tagged: Yellow starthistle

Officials release new weevil to battle yellow starthistle

In April 2021, scientists released weevils from the Mediterranean region of Europe at the Bureau of Land Management Magnolia Ranch day-use area in El Dorado County to join the battle against yellow starthistle. Yellow starthistle rosette weevil is a newly approved natural enemy of yellow starthistle, which was introduced in California more than 150 years ago and, with no natural enemies in its new location, became one of the state's most harmful weeds, infesting nearly 15 million acres.

In California, yellow starthistle can grow to shoulder height, forming massive, thorny patches that block hiking trails, crowd out native plants and present a wildfire danger. The plant is toxic to horses and its flowers are encircled by inch-long sharp spines that can pierce the eyes of grazing animals.

UC Cooperative Extension has worked for decades with landowners to manage yellow starthistle-invested land.

“Over the years, we have developed effective control strategies for yellow starthistle – including well-timed mowing, grazing, hand pulling, burning, cultivation and herbicide application,” said Scott Oneto, UC Cooperative Extension natural resources advisor in El Dorado County. “But these treatments are rarely implemented on a scale large enough to combat our enormous starthistle infestations.”

Efforts to introduce natural enemies from yellow starthistle's home range began in the 1960s. Several species were released to attack starthistle flower heads. These insects lay eggs, hatch and feed on developing seeds, reducing seed production.

“Although the flower head insects sometimes attack high proportions of flowers, yellow starthistle is a very prolific seed producer with an individual plant producing as much as 100,000 seeds,” Oneto said. “Even if the insects reduce seed production by 50%, that still leaves a lot of seeds.”

The newly introduced yellow starthistle rosette weevil, first collected in Turkey as a prospective biocontrol agent in 1984, attacks the plant at the base. Since 2001, United States Department of Agriculture research entomologist Lincoln Smith has studied the insect at the USDA Agricultural Research Service laboratory in Albany.

“Larvae of the weevil develop and feed inside the root crown during spring, adults emerge in June, and then they spend the rest of the year hiding,” Smith said. “There is only one generation per year, so populations will grow slowly, which will gradually reduce yellow starthistle populations.”

The weevil presents no risk to other plants in California except bachelor's buttons, which is an introduced plant from Europe, but not considered a noxious weed. Successful biological control with the weevil is expected to reduce yellow starthistle, but not completely eliminate the weed.

This was the second release of the beneficial insect in North America. The first release occurred in Solano County in April 2020.

Bureau of Land Management and University of California Cooperative Extension researchers will be monitoring the Magnolia Ranch site intensively over the next several years to determine the rate of rosette weevil reproduction and efficacy at feeding on yellow starthistle.

For more information, see A New Warrior Released in the Battle to Control Yellow Starthistle by Scott Oneto on the UC Weed Science blog.

'All You Mead Is Love!' Enroll in UC Davis Online Course by Monday, June 1

Picture this: A honey bee foraging on yellow starthistle (Centaurea solstitialis), an invasive weed that farmers absolutely hate but one...

A honey bee foraging on yellow starthistle, a weed farmers hate but beekeeper, honey enthusiasts and mead makers love. (Photo by Kathy Keatley Garvey)

A honey bee foraging on yellow starthistle, a weed farmers hate but beekeeper, honey enthusiasts and mead makers love. (Photo by Kathy Keatley Garvey)

Due to coronavirus pandemic precautions, the UC Davis mead courses are now online, and Mead Making 201 is scheduled June 22-23 and June 25-26. The deadline to register is June 1. (Photo courtesy of Honey and Pollination Center)

Due to coronavirus pandemic precautions, the UC Davis mead courses are now online, and Mead Making 201 is scheduled June 22-23 and June 25-26. The deadline to register is June 1. (Photo courtesy of Honey and Pollination Center)

USDA approves release of weevil to control yellow starthistle

The USDA has announced it will allow the release of a weevil (Ceratapion basicorne) in the United States to help control yellow starthistle, an invasive weed found in 40 of the lower 48 states, reported Capital Public Radio. The weevils will initially be released in California.

Ceratapion basicorne is native to Eurasia, the same area where yellow starthistle originated. Yellow starthistle is thought to have been introduced into California from Chile during the Gold Rush. The weed readily took hold in California valleys and foothills, thriving in areas where the soil has been disturbed by animals grazing, road construction and wildland firebreaks. Today, yellow starthistle is a very common sight in vacant lots and fields, along roadsides and trails, in pastures and ranch lands, and in parks, open-space preserves and natural areas.

Capable of growing six feet tall and bearing flowers surrounded by inch-long spines, yellow starthistle reduces land value, prevents access to recreational areas, consumes groundwater and poisons horses.

Brad Hanson, UC Cooperative Extension weed specialist at UC Davis, says yellow starthistle thrives in part because of its prickly spines.

"It's not very palatable to any livestock, especially once it's started to flower . . . . Often times, the other grasses and more palatable plants are grazed and the starthistle persists and is sort of the only thing left,” he said.

Hanson says yellow starthistle can be managed on a small scale with chemicals, but that method just doesn't work with the scale of infestation in the state.

“It's difficult to control economically on the millions and millions of acres of rangelands or non agricultural lands that are sort of minimally managed,” he said.

The USDA's environmental assessment of the weevil found no significant impact of its release, besides helping to control yellow starthistle infestations.

California budget cuts impact yellow starthistle control

The Star Thistle Leading Edge Project, a collaborative effort involving state and federal agencies and UC Cooperative Extension, is facing a lack of funding, reported Matt Weiser in the Sacramento Bee.

The project was funded by the state Department of Food and Agriculture as part of its weed control budget totaling $2.7 million in 2011. That money was cut from the 2011-2012 state budget cycle. Local and federal grants that kept the program going will run out next month. A $314,000 grant from the Sierra Nevada Conservancy was denied because the group failed to meet the application requirements, the article said.

These developments may give starthistle a bigger hold on California wildland. The roots of the nuisance weed grow as much as six feet deep to find moisture.

"It would be as if these areas are experiencing drought because of the amount of water it uses," said Joe DiTomaso, UC Cooperative Extension specialist in the UC Davis Department of Plant Sciences. DiTomaso is a leading expert on starthistle.

The Leading Edge Project started about a decade ago with a mapping effort to find out just how much of the state was infested with starthistle, and where it was spreading, said Wendy West, the project's coordinator and a University of California Cooperative Extension program representative based in Placerville.

"It felt like such a losing battle that we really needed to prioritize what we could do and how we could be successful," West said.

"I've personally pulled plants at 7,000 feet in Alpine County," West said. "It may not move quite as fast, but yellow star thistle is a really good example of a plant that can adapt to new locations easily."

Time to plan your yellow starthistle weed attack

Weeds, weeds, weeds!  Have you noticed?  This has been a banner year for weeds.  Puncturevine where I’ve never seen it before. Garden soil covered with common purslane (at least it’s good in salads). And solid stands of yellow starthistle everywhere!

Our cool late spring and repeated late rains created multiple germination periods; weed seeds in the soil had many opportunities to sprout. And sprout they did! With the heat of summer, weeds flowered and became noticeable. Now, weeds have set seed and dried along roadsides, in fields, and landscapes. All those weed seeds will require diligent effort next spring! It’s time to plan your weed attack to prevent next year’s seedlings.

What can be done? First of all, identify your weeds. Different weeds require different treatments. Is it an annual or perennial? Does it propagate by wind-blown seeds or by runners? The University of California Integrated Pest Management website, has weed-identification guides that are fun and easy to use. The website also offers treatment guidelines.

In the California foothills, yellow starthistle (YST) is perhaps the most common weed of concern. It impacts much of our open space - agricultural and rangeland - and intrudes into our neighborhood landscapes. Yellow starthistle currently infests more than 15 million acres of land in California. Not only does it prevent recreational use, like walking or hiking, but it chokes out native grasses and wildflowers. It is also poisonous to horses, causing a neurological disorder called "chewing disease” which can be fatal once symptoms develop.

More and more, individual homeowners are becoming the key to containing and eliminating this invasive plant, wherever it exists.  The goal in treating yellow starthistle is to prevent seed formation.  Unfortunately, this year's YST has already bloomed, set seed, and dried. Planning is essential to prevent another banner crop next year.

That said, yellow starthistle can be hand-pulled at any time in its lifespan. In its present dry and spiny stage, pulling the weeds can inflict pain, so be sure to wear gloves. Double-bag the plants and burn them later in the fall.

There is a fairly new herbicide (2009) on the market from Monterey Chemical called Star Thistle Killer.

It is available at home centers and nurseries and can be purchased without a permit. The active ingredient, clopyralid, is the same active ingredient in Transline and should not be used on lawns. However, one spray application on small parcels of less than two acres during the late fall, winter, or early spring rainy season will be effective in preventing yellow starthistle seedling germination next spring.

Local pest control companies are also available to provide a one-time herbicide application for yellow starthistle.  For more information, go to the Central Sierra Cooperative Extension website or call the Yellow Starthistle Leading Edge Project in the UC Cooperative Extension office at (530) 621-5533 or (209) 533-6993.

Information adapted from the University of California Integrated Pest Management Program and from “Yellow Starthistle: Brief Homeowner Information Sheet” by John E. Otto, Amador County Master Gardener.

Also see the following video on yellow starthistle control.

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