Ever wonder how that spiny yellow-flowered thistle came to be almost everywhere you look in the Sacramento Valley? This extremely resilient plant is exceptionally hard to eradicate, and often takes several years of intensive management to be able to control. Starthistle (Centaurea solstitialis) can spread rapidly and take over sides of roadways and pastures in practically no time, and many landowners are at a loss of how to get rid of it without breaking the bank. Fortunately there are several strategies that can be tailored to a landowners goals whether they seek to stop the spreading of the weed or to eliminate it completely.
Mowing is a common practice along highways and in recreational areas. It is most successful at the spiny to early flowering stage. Mowing too early can allow the starthistle to recover and can suppress competing vegetation which enhances light penetration and can increase the problem according to the California Invasive Plant Council.
Grazing is an effective tool for managing star thistle and the results are somewhat similar to that of mowing. Cattle, goats, and sheep will all graze the plant, and goats will even eat it after the spiny stage. The most effective period for grazing starthistle is from May to June, using large numbers of animals for a short duration in order to reduce plant height and the production of seed. While this is an effective strategy, extra precaution must be taken to avoid overgrazing other desired forage.
Although a more controversial method for controlling starthistle, prescribed burning has been proven to be a very effective tool for managing the weed. Burning should be done at the very end of the rainy season, right when the yellow flowers appear. Burning for 2 or more consecutive years helps suppress yellow starthistle and deplete the soil seedbank.
It is important for landowners to keep in mind that achieving control over a starthistle invasion cannot be accomplished in one season since their seed can be viable for three years, or possibly longer. Once the starthistle has been treated and suppressed, it is important to reestablish desired grasses to avoid absence of competition that will allow the starthistle to reestablish. With proper management and utilization of these methods, a land owner should find success in limiting further spreading of starthistle at the very least.