We regularly highlight noxious and invasive species, sharing defining characteristics to help you identify it in the field as well as providing treatment recommendations to help you get rid of it. In this Invasive Watch, we feature Scotch thistle.
Scotch thistle is a biennial or annual forb that can grow up to 8 feet tall and 6 feet in width with branching, spiny leaf wings that extend down onto the stem and are covered with dense, fine hairs. Leaves are large, closely lobed, hairy and lined with sharp spines. Flowers are numerous with spine-tipped bracts and are violet to reddish-colored. The plant typically produces a large, ground-level rosette in the first year and becomes a tall, spiny plant in its second year.
Scotch thistle reproduces by seed, and each plant is capable of producing 8,000 to 40,000 seeds, which may remain viable in the soil for 30 years. Plumed seeds can be dispersed by attaching to clothing and animal fur, by being transported in hay and machinery or by being carried by wind and water.
Scotch thistle is often found along roadsides, irrigation ditches and waste areas, in pastures and on rangelands. The plant is native to Europe and Asia and was introduced to the United States in the late 19th century as an ornamental plant. It’s now considered a major noxious weed and has spread to most states across the United States. It spread rapidly into dense stands that prohibit foraging by wildlife and livestock and is difficult to eradicate because of its drought resistance.
Apply 2.85 ounces per acre of TerraVue™ herbicide in fall to seedlings and rosettes before the ground is frozen, or in spring and early summer to rosette or bolting plants. An additional option is an application of 2.5 to 3.3 ounces per acre of Opensight® herbicide, again, in fall to seedlings and rosettes before the ground is frozen, or in spring and early summer to rosette or bolting plants.
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Label precautions apply to forage treated with TerraVue or Opensight and to manure and urine from animals that have consumed treated forage. Consult the label for full details.
™ ® Trademarks of Dow AgroSciences, DuPont or Pioneer, and their affiliated companies or their respective owners. Opensight, Rinskor and TerraVue are not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions.
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