Noxious weed of the month: yellow starthistle

By Ethan Proud
PREVIEW Columnist
A noxious weed that has yet to be reported in Archuleta County is the yellow starthistle, which is a List A noxious weed. List A designates the species for eradication, typically by chemical means, though the most effective and economic treatment type can be used.
Yellow starthistle can be recognized by its obviously yellow flower and the 1-inch spiny bracts just beneath the disc florets. Yellow starthistle has only been reported in a few Colorado counties and is absent from Archuleta County for the time being.
Yellow starthistle is an annual, and populations can exhibit explosive growth patterns, producing 100,000 seeds that can persist in the soil for up to four years. Young plants are green, while the color fades as plants mature and becomes grayer and is characterized by hairy leaves.
Yellow starthistle belongs in the genus centaurea, making it a knapweed, and should not be mistaken for sow thistles (sonchus genus), which also grow in Archuleta County. Knapweeds form a basal rosette and have many stems which branch from the base, giving it a bushier appearance than the common thistles found in southern Colorado.
Yellow starthistle is a major concern of ranchers and ag producers, as mature plants are highly toxic to horses and cause chewing disease. The plant contains neurotoxins that destroy the pathway that controls chewing. Horses that eat the plant develop a taste for it and signs of toxicity occur months after feeding on large quantities. After a horse has been poisoned with yellow starthistle, it will no longer be able to consume food and will starve. Horses that have eaten yellow starthistle will move their face along the ground, as if they were eating , but will not actually graze.
Russian thistle, a common List B Species in Archuleta County, also causes chewing disease.
Please notify Archuleta County Weed and Pest if you have seen or believe you have seen yellow starthistle.
Archuleta County Weed and Pest is your local resource for managing noxious weed populations and controlling other pests.
CPR and first aid classes
CPR and first aid certification classes are offered monthly by the Colorado State University Extension office on the second Monday and Wednesday of each month from 6 to 10 pm. Anyone needing to receive or renew certification can register by calling the Extension office at 264-5931.
We will also attempt to schedule classes on additional dates with five or more registrations. Cost for the classes is $80 for combined CPR/first aid and $55 for CPR, first aid or recertification. The type of first aid information provided will vary by the needs of the audience.

This story was posted on September 9, 2018.