Impacts on Utah Rangelands and Methods of Control
Squarrose knapweed (Centaurea squarrosa, Centaurea virgata) is an invasive perennial weed impacting many areas of rangeland in Utah. Squarrose knapweed (Cs) is problematic due to its competitive nature, which reduces native grasses, shrubs and forbs that are so imperative for wildlife and livestock. Squarrose Knapweed’s invasiveness can be qualified by its ability to thrive in shallow, dry soils, survive harsh climates, relatively high fire tolerance, successful seed dispersal methods, the ability to remain as a rosette for years in unfavorable conditions and its capacity to take over large areas of once healthy rangelands or exposed, disturbed areas. To effectively control the spreading of squarrose, a variety of methods must be employed. In order to successfully control the spread of squarrose, a potential management plan must integrate biological, chemical, cultural and mechanical control, attacking the satellite populations first and working inbound toward the main infestations.
In order to understand the problem squarrose presents rangeland managers, and to distinguish common characteristic of squarrose, the weed must be examined in modest detail. The Weeds of the West, now in its ninth edition, is the authoritative standard for basic information. Paraphrasing from that book general information as follows can be gathered. From the Asteraceae family, squarrose, a native to the eastern Mediterranean area, is a taprooted, long-lived perennial with heights reaching 12-18 inches. To distinguish squarrose from other knapweeds, it is important to note that the flower heads are pink and relatively small, holding three to four seeds. The seed heads are deciduous and fall from the stem after seed maturation. Bract tips, the most distinguishable feature of squarrose from other knapweeds, are recurved, and the terminal spine is longer than the lateral spine on each bract (Whitson, et al., 2006). A lengthy paraphrase, but important in its detail of just how squarrose differs from othe knapweeds and how it functions as a weed. In figure one, a close up of a squarrose knapweed head, listed at the end of the paper, though not comparing it to the other knapweeds, it reveals the distinctive recurved or bent bract singular to squarrose. Once spotted, especially in a native scene, these bracts can be the easiest way to tell squarrose apart.