Yellow starthistle is unwelcome

UNR Cooperative ExtensionA close look at the yellow starthistle flower shows its nasty spines.

UNR Cooperative ExtensionA close look at the yellow starthistle flower shows its nasty spines.

Be wary when you spot bright yellow flowers. Although they may appear beautiful from a distance and entice you closer for a better look, if they are flowers of the noxious weed yellow starthistle, you may stab yourself on their 1-inch spines.

Yellow starthistle (YST) is a winter annual that germinates in early spring and is blooming heartily now. It is a member of the Aster family. It has yellow dandelion-like flowers, 3-foot-deep roots and 3⁄4- to 1-inch spines. These nasty spines pierce most fabric, so once you try to walk through an infested area, you will never forget YST.

First discovered in 1869 in Sacramento, YST has infested almost 23 million acres in California. It is now invading Nevada. Recreationists, ecologists, ranchers, farmers, natural resource people and land managers all strongly agree - let's keep yellow starthistle out of as much of Nevada as possible! Although it is found in 11 out of 17 Nevada counties, vigilance and removal of early arrivers are the most effective and least costly methods of dealing with this weed.

Why are we so concerned about this plant? After all, it is not a perennial, so it isn't long-lived. It comes back only from seed, rather than from roots, but it is a prolific seed producer. Average seed production ranges from 20 to 120 seeds per seedhead. A single plant has the potential to produce up to 150,000 seeds. Infestations can produce 50 to 100 million seeds per acre. Ninety-five percent of the seeds produced are viable and will germinate the following year whenever soil moisture is available and temperatures are favorable. Seeds that do not germinate in the first year can remain viable in the soil for 10 years.

Grazing animals avoid infested rangeland. Horses may die from "chewing disease" if they eat YST. Once an area converts to a YST monoculture, wildlife lose valuable habitat. YST can greatly reduce or eliminate the economic value of pastures and hay fields. Land becomes unusable for recreation.

Hand-pulling works to reduce YST in small areas. Cattle and sheep may graze it before flowering, but after flowering only goats will eat it. Mowing is possible, but plants may not die and just grow close to the ground. There are herbicides to control YST, but timing the application is critical and chemicals can kill desirable plants. Revegetation with desirable species is a critical component in restoring an YST infested site.

YST infestations are being mapped across the state, so if you find infestations, let me know. The more watchful eyes, the better to prevent the spread of YST.

• JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension and may be reached at or 887-2252.


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