Help control yellow starthistle

Nevada is greening up. Unfortunately, mixed in with that luscious green vegetation are noxious invaders that are ready to infest and take over native species habitat. Yellow starthistle is one of these.

This winter annual that germinates in early spring, is a member of the aster family. It has yellow dandelion-like flowers, 3-foot-deep roots and three-quarter- to 1-inch spines. These nasty spines pierce most fabric, so once you try to walk through an infested area, you will never forget yellow starthistle.

First discovered in 1869 in Sacramento, yellow starthistle has infested almost 23 million acres in California. It is now invading Nevada. Recreationists, ecologists, ranchers, farmers and natural resource and land managers all strongly agree that we must keep yellow starthistle out of as much of Nevada as possible. It has already been found in 11 of Nevada's 17 counties. Being vigilant and removing early arrivers is the most effective and least costly way to control the spread of this weed.

Why are we so concerned about yellow starthistle? After all, it is not a perennial. It comes back only from seed, not from its roots. The problem is, it is a prolific seed producer. Average seed production ranges from 20 to 120 seeds per seed head. 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. To make matters worse, seeds that do not germinate in the first year can remain viable in the soil for 10 years.

Grazing animals avoid rangeland infested with yellow starthistle. Horses may die from "chewing disease" if they attempt to eat it. Once an area converts to a yellow starthistle monoculture, crowding out other native vegetation, wildlife lose valuable habitat. Yellow starthistle can greatly reduce or eliminate the economic value of pastures and hayfields. Land becomes unusable for recreation.

Hand pulling can control yellow starthistle in small areas. Cattle and sheep may graze it before flowering, but after flowering, only goats will eat it. Mowing is an option, but mown plants may not die. They may only grow closer to the ground. There are herbicides to control yellow starthistle, but applying them at the right time is critical, and the chemicals can also kill desirable plants. After control measures are taken, revegetation with desirable species is critical to restore the site to its natural state and keep starthistle from reinstating itself.

Please, keep you eyes open for this nasty weed. If you find infestations, let me know. The more watchful eyes we have, the better job we can do in preventing the spread of yellow starthistle.

For information on weeds and gardening, contact me at skellyj@unce.unr.edu or 877-2252 or your local University of Nevada Cooperative Extension office. Check out horticulture publications at www.unce.unr.edu. "Ask a Master Gardener" at mastegardeners@unce.unr.edu.

-- JoAnne Skelly is the Carson City/Storey County Extension Educator for University of Nevada Cooperative Extension.