Thorny Yellow Weed Harms Horses

Yellow starthistle is a noxious weed with one-inch spines radiating out from the base of the flower. Infested land can become impassable due to these spines reducing recreation. This weed successfully depletes soil moisture and eliminates desirable plants. It crowds out native plants, destroying valuable wildlife habitat and food sources. And, if these aren’t reasons enough to control it, long-term ingestion of yellow starthistle can poison horses with chewing disease. The first signs of poisoning are twitching of the lips, tongue flicking and involuntary chewing. Permanent brain damage can result and horses may die of starvation.

Yellow starthistle is an annual, developing, flowering and seeding all in one season. Each plant can produce nearly 75,000 seeds, resulting in 50 to 200 million seeds per acre for heavily infested areas. Most seeds germinate the following year, but some remain in the soil for as long as 10 years before germinating.

The plant is gray-green with a long taproot. It has bright dandelion-yellow flowers with sharp spines coming off of the flowers. It may grow from 6 to 72 inches tall depending on the site conditions and water availability.

Control of yellow starthistle starts with knowing what the plant looks like and getting rid of it before it goes to seed. Early detection, prevention and control are critical. Awareness of where the weeds are and communicating with neighbors about infested areas, alerting each other to new infestations and working together to control the weeds will help reduce the spread of this competitive invader. Because it is an annual plant, pulling the weeds out prior to seeding goes a long way to reducing small infestations.

While there are herbicides that are effective, when used repeatedly they may cause an increase in other weeds and yellow starthistle resistance to the herbicide. Herbicides with the active ingredient 2,4-D (a long chemical name for which this is the abbreviation) work well as spot treatments for occasional weeds, but will not stop germination of seeds. Drought stress limits the effectiveness of most herbicides. Only use herbicides in combination with other control methods and a re-vegetation program.

Save our open spaces and protect horses by controlling and reporting yellow starthistle infestations. If you think there is yellow starthistle on your property, know of its existence or want to have a weed properly identified, please contact Carson City Weed Coalition Coordinator Margie Evans here at the University of Nevada Cooperative Extension office – 887-2252,