Ranchers in Northern Nevada's remote Paradise Valley first noticed the weed some 20 or 30 years ago. Growing sparsely and mainly in sagebrush-covered foothills, the plant wasn't really much cause for concern. It is now, with Medusahead quickly spreading and in some places, replacing prime grazing range with a weedy "wasteland," said Daryl Riersgard, a Paradise Valley rancher and coordinator of the area's weed control district. Believed introduced in the United States as a seed contaminant in the 1800s, Medusahead already infests 2.5 million acres and is spreading at a rate of 12 percent per year, according to a study released this month by researchers at Oregon State University. The weed crowds out native vegetation and profoundly impacts grazing range. Livestock, deer and elk won't eat the spiny weed because it hurts their mouths and is high in silica. According to the study, once established, Medusahead reduces an area's grazing potential by 80 percent. High silica content also causes mats of the weed to remain on the ground after it dies "like a thick, cheap carpet," Riersgard said...
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