Story 2: Managing Yellow Starthistle in Northern California

For almost 30 years the Stone family has owned and operated the Yolo Land & Cattle Company. Like landowners in other parts of northern California, Henry Stone and his sons Scott and Casey have fought against nonnative plants invading their property. These invasive plants cause countless problems and add considerable costs to ranch operations. One of the major culprits is yellow starthistle (Centaurea solstitialis L.), which was most likely introduced to this country in the mid-1800's from Europe and the Mideast. Yellow starthistle is a widespread problem in Northern California but land managers at Yolo report promising results in preventing yellow starthistle from taking over the ranch and destroying valuable grazing land.

According to Casey Stone, approximately 15 - 25% of the 7,500-acre Yolo ranch is infested with yellow starthistle. "It will eventually take over an area and crowd out everything," he explains. The weed chokes the growth of native grazing plants, and its spiny thatch is difficult for dogs and horses to maneuver through. The spread of yellow starthistle also increases erosion since its shallow roots provide less soil stability than the deeper-rooted native plants it displaces. Yellow starthistle is a significant problem for both the cowboys who work the ranch and the 500 head of cattle who graze on the native grasses and forages that grow there. The Stones don’t know how the plant was first introduced to their property but suspect that it may have spread from nearby roadways. Yellow starthistle is commonly found along roads and fences and spreads easily onto flat areas of the terrain.

A variety of weed management methods have been tried at Yolo including biological, chemical, and mechanical control, all of which are used primarily on flat terrain. Growth of yellow starthistle is usually initiated by fall rains and results in small, basal rosettes. The Stones have experimented with flash or short-term grazing during the rosette stage of growth to eliminate the weed at an early stage of development. However, flash grazing has proven less effective with cattle, who are highly selective foragers, than it has with other species such as sheep or goats. Controlled burning, particularly of plants growing on steep terrain, has been effective when used on a biennial basis but is becoming a less viable option due to stricter local air quality regulations. The California Department of Food and Agriculture has tried using weevils to control the weed at Yolo, but their success has been limited. "Chopping the skeletons" or mechanically removing senesced plants from the landscape, another commonly used control method, is useful for clearing heavily infested areas but has also been blamed for spreading the weed statewide by shattering and spreading the seedpods. With the current price of fuel in California, it is also becoming an increasingly expensive method.

Chemical control methods have proven the most effective for the Yolo Land & Cattle Company and have been used extensively by the Stones to stop yellow starthistle in its tracks. They have achieved success in controlling the weed by rotating the use of chemicals to avoid weed resistance. The Stones note that while chemical control of yellow starthistle on steep terrain is cost prohibitive due to the need to spray from a helicopter, control on flat terrain has been cost-effective. Greatest success was achieved by applying chemicals every other year, and performing controlled burns whenever possible.

While the Stones have had considerable success in controlling the invasion of yellow starthistle on their ranch, formidable challenges remain. Invasive weeds know no boundaries and consistent weed management must be practiced district-wide in order to maintain results. And while effective practices for the control of yellow starthistle have been found, new invasive plant threats have emerged on the grasslands. The Stones have found in recent years that when they gain a foothold on yellow starthistle, it is often replaced by barbed goat grass or Medusa head grass, two very invasive late season grasses that cattle won't eat. Both weeds create a thick thatch that prevents beneficial plants from emerging, and the only proven control method is burning. The Stones are currently working with several local conservation groups to find ways to combat this new problem. Meanwhile, they have contrived some benefit from the remaining yellow starthistle. "We learned it makes some of purest honey available," Casey says "so we created a honey label, partnered up with a local beekeeper and sell the honey to regional stores".

See the Yellow starthistle species profile for more information.