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Published online by Cambridge University Press: 12 June 2017
Bristly thistle (Cirsium horridulum Michx.) is an important perennial weed in Alabama pastures. It may remain vegetative many years before flowering and may regrow from the roots after flowering. A heavily infested pasture produced about 10,000 seedlings per acre per year of which 73% established from January through April. There was an average of 150 achenes per head but many did not contain fully developed seed. Essentially equal numbers of red and yellow flowered types were found. From two to as many as six successive cuttings below the soil surface were necessary to kill thistle plants. Thistles were effectively controlled by 2,4-dichlorophenoxyacetic acid (2,4-D), and 2-methyl-4-chlorophenoxyacetic acid (MCPA).