   Yellow Starthistle - September 1, 1999 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Noxious weeds are a growing concern in wildland areas, along roadsides, and even in urban landscapes. A noxious weed is: a weed specified by law or regulation to be particularly undesirable, destructive, and difficult to control. Yellow starthistle (Centaurea solstitialis) is a noxious weed that can be found in isolated areas of Cottonwood and many places in Camp Verde. Although the infestations are small, yellow starthistle spreads very rapidly and we need to be concerned. Yellow starthistle is native to the Mediterranean region of Europe. It is thought that it arrived in North America in alfalfa seeds shipped to California during the mid 1800's. Today it can be found in 23 of the contiguous 48 states. It now covers over 10 million acres in California and is increasing rapidly in Idaho, Oregon, and Washington. In the west, yellow starthistle poses the most serious threat to semiarid rangelands but also can infest orchards, roadsides, ditch banks, and parklands. Aside from being invasive, yellow starthistle is poisonous to horses and causes Achewing disease@ a fatal neurological disorder. Yellow starthistle is a winter annual with bright yellow flowers. The flowerheads are single on the end of short branches. The flowers are armed with stout, straw-colored spines 1 to 2 inches long. In the spring, the plant consists of a rosette that lies close to the ground. In early summer, the stems elongate to produce a plant that ranges from 4 inches to 5 feet tall. Later in the growing season, flowers fade to a dull straw color. The flowerheads produce abundant seed. Some of the seeds are plumed and disperse quickly. The plumeless seeds persist in the flowerhead until the plant is disturbed. Seeds are spread to new areas by wind, in the fur and feathers of animals and birds, by animals and birds eating seeds and passing them through their gut, and by human activity. In California, human activity probably accounts for most of the seed dispersal. Here, they are transported to uninfested areas by livestock, vehicles, tractors, heavy equipment, shoes, in loads of hay, by flowing water, and other means. Approximately 95% of the seeds are viable and 10% of the seed can remain dormant for more than 10 years. These dormant seeds create the greatest challenge for land managers because these seeds re-invade sites rapidly after control efforts. Management of yellow starthistle requires and integrated approach that prevents further introductions, detecting and eradicating new introductions, containing existing infestations, and controlling large-scale infestations. There are methods of control available to land managers. An integrated approach can utilize several strategies: prevention, hand pulling, mechanical control, revegetation, herbicides, grazing, and biological control. Prevention strategies include buying certified weed-free hay, cleaning of equipment used in infested areas, and monitoring. Mechanical control strategies are hand pulling and bagging in plastic bags and tillage before flowering. The bagged plants should be taken to a landfill and buried as quickly as possible. Revegetation strategies replace the yellow starthistle with more desirable cool season perennial grass species. Herbicides are very effective. Selective herbicides, such as 2,4-D, kill only broad leafed plants. Nonselective herbicides kill everything and areas must be revegetated after treatment. Grazing strategies utilize cattle, goats, or sheep to remove starthistle and give existing desirable plants a competitive advantage. Grazing should be carefully timed to remove plants as they bolt out of the rosette stage and prior to the spiny flower stage. Biological control is one of the most important practices in an effective noxious weed management program. There are several insects that have been imported from yellow starthistle=s native range. To date, three weevils and three flies have shown promise and have been released. These insects attack flowers utilizing several different strategies. They can never offer 100% control, but can have a great impact when combined with one or more of the strategies outlined above. If you see any yellow starthistle on or near your property, pull it out and double bag it in plastic bags. Each of us can help control and eradicate noxious weeds. Successful efforts require teamwork and cooperation on all land ownerships. If you need assistance in identifying yellow starthistle, pick a flower and seal it in a plastic bag so that no seeds will escape. Take the sample to the Cottonwood Cooperative Extension office have it identified. In addition, a detailed description of the plant location would assist us in knowing the extent of the yellow starthistle infestation in the Verde Valley. For more information or assistance in identifying noxious weeds or if you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. |