LAKE COUNTY, Calif. – According to the California Invasive Plant Council, invasive weeds cost Californians about $82 million a year just on control, monitoring, and outreach.

Estimating actual ecosystem impacts is harder to quantify, but costs have been calculated in the billions nationally.

This is the first in a series of articles is intended to bring an awareness of invasive weeds by showing how to identify them, discussing their growing habits, and offering ways to manage them, either on your property or helping out elsewhere.

First up is yellow starthistle.

Centaurea solstitialis is the scientific name for Yellow Starthistle. It grows in sunny areas, usually below 7,000 feet, and where the rain fall is between 10 to 60 inches. That’s a whole lot of California.

You’ll find it in many grasslands, pastures, abandoned lots, along hiking trails and roads. It’s the bully of pastures, crowding out native grasses and forbs.

Control efforts have proven more or less effective; more effective because they do work at decreasing plant population, less effective because the minute your back is turned it comes back twofold.

As a native to southern Europe and accidentally introduced to California in imported alfalfa seed, this thorny devil has no natural predators giving it a competitive edge that it really doesn’t need. It already has an impressive array of survival techniques.

For starters, it’s a prolific bloomer, creating dense impenetrable stands that can produce 50 to 100 million seeds per acre. It’s extremely drought tolerant with greedy roots reaching to depths of 5 feet. It uses so much soil moisture that, even in wet years, it can create drought conditions for native species.

The seeds spread by using their barbed spines to hitchhike on an animal’s hide, people’s clothing or vehicle undercarriages. Otherwise the seeds, left alone, don’t fall far from the bush. Although most of the seeds germinate quickly when the conditions are right, they can stay dormant for three to four years.

The environmental consequences of yellow starthistle are numerous. Their water consumption has been estimated at 46,000 acre feet a summer from the Sacramento River watershed. Compare that to the volume of Clear Lake at zero Rumsey, 842,000 acre feet. That’s about 5 percent of the lake.

Because they produce dense stands they reduce the productivity of pasture land, in some cases up to 50 percent, meaning each acre supports less livestock. In addition, yellow starthistle is toxic to horses causing a neurological condition called “chewing disease,” characterized by brain lesions and ulcers in the mouth. There is no cure.

Because this weed is so pervasive throughout the western states, eradication efforts have long been abandoned; you can’t put the genie back in the bottle.

However, there are biological control methods that have been tried with some success. Two weevils have been released, one accidentally and the other on purpose. These weevils lay their eggs in the flower heads which reduces seed production.

Then, in 2003, a rust fungus specific only to Yellow Starthistle was released. The stress it causes on the plants reduces seed production. Time will tell how successful these measures are at keeping it in check. Keep your fingers crossed!

For us laymen, what can we do? Besides volunteering for weeding efforts, we can try weeding it from our own yards or maybe even the abandoned lot next door.

One way to rid them from your yard is to pop them out with a shovel. Insert the shovel under their base of the plant and push down on the end of the shovel. You’ll hear a very satisfying “pop” as the root breaks free. If the plant already has yellow flowers put it in the recycle bin. You don’t want the seeds going back into the soil.

This method takes several years and a lot of work. It took me two years to remove it from my three-acre yard and still each year one or two pop up. With starthistle you can never rest on your laurels.

Another management strategy is to cultivate or rototill the entire affected area. Since yellow starthistle begins emerging with the fall rains and continues to germinate throughout the rainy season, a single cultivation when soils dry out in late spring kills this year’s plants. You may need to cultivate several years in a row depending on how bad your infestation is.

A well-timed mowing, while not as effective, can help manage starthistle. But it must be well-timed: Too soon and the plants will “pincushion,” forming flowering mounds just below the mower, too late and mature seeds will continue developing even after having been mowed down. Let the basal rosettes bolt into high stocks, then mow when the plants are between the staring and flowering stage.

For more management techniques visit http://ipm.ucanr.edu/PMG/PESTNOTES/pn7402.html.

For a comprehensive study of yellow starthistle, see the Invasive Plant Council’s “Yellow Starthistle Management Guide” at https://www.cal-ipc.org/docs/ip/management/pdf/YSTMgmtweb.pdf.

See how the California Invasive Plant Council determines economic losses to the state at https://www.cal-ipc.org/docs/ip/research/pdf/Cost_of_Invasive_Weeds_in_California.pdf or https://www.invasivespeciesinfo.gov/economic/state.shtml ,

Karole Ward is a member of the UC Master Gardeners Program.