MANHATTAN, KAN. -- The musk thistle control season has arrived, and the Kansas-wide noxious weed is alive and doing well, said Walt Fick, range and pasture management specialist with Kansas State University Research and Extension.
Knowing the musk thistle's life cycle is important to getting a good control strategy in place, Fick said. The weed is primarily a biennial or winter-annual plant.
"As a biennial, seed will germinate in the spring and the plants will remain as rosettes during the entire growing season. Then, after surviving a winter, the plants will bolt, flower, and produce seeds, thus taking parts of two growing seasons to complete their life cycle," he explained. "As a winter annual, musk thistle emerges in the late fall with moisture. The plants go through the winter, then produce seed the following year."
Musk thistle only reproduces by seed. Thus, the goal of any control program is to reduce and/or eliminate seed production, Fick said.
Control options include mechanical, biological, cultural, and chemical methods, the agronomist said. These options include:
Once plants begin to bolt, products such as picloram + 2,4-D (Tordon 22K + 2,4-D), metsulfuron + 2,4-D (Escort XP + 2,4-D), metsufuron + chlorsulfuron (Cimarron Plus), metsulfuron + dicamba + 2,4-D (Cimarron Max), or aminopyralid alone (Milestone) or in combination with 2,4-D (ForeFront R&P) are more effective. For bolted to bud stage thistles, products containing clopyralid (Curtail and Stinger) provide excellent control.
"In other words, treat musk thistle before it starts to bloom," Fick said. "Although some herbicides, such as metsulfuron, have proven to reduce seed viability when applied at the bloom stage, they are unlikely to eliminate all seed production. And, it only takes one seed to keep the population going."
Herbicide recommendations for musk thistle control are available in "2009 Chemical Weed Control for Field Crops, Pastures, Rangeland, and Noncropland." That publication is available at any county or district K-State Research and Extension office, as well as on the Web.
"Always read the herbicide label, too," Fick advised, "paying particular attention to precautionary statements, grazing or haying restrictions, and rates of application."