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How to Control Scotch Thistle
How to Control Scotch Thistle. Sometimes called cotton or woolly thistle, Scotch thistle (Onopordum acanthium) is a weed. Although it prefers moist sites, it can thrive along roadsides, among crops and in pastures. Scotch thistle is biennial, meaning it only flowers every other year. Its first year is spent producing the rosette from which the...
Sometimes called cotton or woolly thistle, Scotch thistle (Onopordum acanthium) is a weed. Although it prefers moist sites, it can thrive along roadsides, among crops and in pastures. Scotch thistle is biennial, meaning it only flowers every other year. Its first year is spent producing the rosette from which the flower stalks will emerge the following spring. If not controlled, the plant can grow to 12 feet tall and spread 5 feet. Integrated pest management specialists with the University of Nevada Extension suggest a three-pronged approach when battling Scotch thistle: mechanical, chemical and cultural.
Things You'll Need
Protective clothing
Goggles
Hoe or shovel
Herbicide
Pull small infestations by hand. Because the plants are covered with spines, wear protective gloves, clothing and eye gear.
Dig into the soil around the base of the rosette on first-year plants and completely sever the roots with a hoe or shovel.
Apply herbicide to the plant in the rosette stage for the most effective control. IPM specialists with the University of Nevada suggest using herbicides that contain one of the following ingredients: clopyralid, dicamba, MCPA, picloram or 2, 4-D. This is best done in the fall and applied at the rate specified, and according to the directions, on the label.
Spray larger plants in the summer or fall, using an herbicide that contains one of the following chemicals: chlorsulfuron, clopyralid or metsulfuron. Apply the herbicide at the rate suggested on the label.
Revegetate the area after ridding it of Scotch thistle. Grass competes with the thistle, generally not allowing it to gain a foothold.
Tips & Warnings
If you have any questions on which herbicides to use, contact your county cooperative extension office for advice.
