Ranchers find the infamous purple flowers of biennial thistles in their pastures – year after year. Break the cycle. Treat them with DuraCor® herbicide during the rosette stage for best control.
Bull, musk and plumeless thistle (Cirsium vulgare, Carduus nutans and acanthoides) germinate in the summer and fall and overwinter as a rosette. The following spring, biennial thistles resume vegetative growth, bolt and then flower. Purple flowers are the identifying factor among the three species. Numerous flower heads are produced from May to October, depending on the species.
Bull thistle is erect, 2 to 5 feet tall with many spreading branches, spiny wings from leaves. Rosette formed first year; flowering stem elongates second year. Leaves have short prickles on the surface and are cottony below. Flowers are dark purple and somewhat clustered.
Musk thistle is erect, freely branching, up to 7 feet tall. Leaves are dark green with light midrib, hairless on both sides, with long, sharp spines. Flowers are deep rose to purple, up to 3 inches in diameter. Branching plant with spiny wings that extend up to flowers.
Plumeless thistle stems grow 1 to 4 feet tall. Rarely flower the first year. Flowers are purple to pink, 1 to 2 inches in diameter, solitary or in clusters of two to five. Bracts are sparsely to densely hairy.
Bull, musk and plumeless thistle are native to Eurasia and were introduced into North America as seed contaminants. Spreading by seed only and producing 8,400 seeds per plant with plumeless thistle to 20,000 seeds per plant from musk thistle. Biennial thistle species can be found across the United States invading overgrazed or otherwise disturbed pastures, rangeland, roadsides and waste areas.
Since biennial thistles reproduce only from seed, the key to a successful management program is to control the plants before flowering. For best control, apply 16 to 20 fluid ounces of DuraCor® herbicide per acre or 24 fluid ounces of NovaGraz™ herbicide plus 1% MSO v/v per acre or 1.2 to 1.5 pints of GrazonNext® HL herbicide, or 20 to 32 fluid ounces of GrazonPD3™ herbicide per acre, during the rosette stage early in the season. Fall to early winter applications can be made to rosettes prior to the first hard frost
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White clover and annual lespedeza exhibit some initial injury (such as lodging and loss of vigor) but recover. NovaGraz™ and DuraCor® are not registered for sale or use in all states. Under normal field conditions DuraCor is non-volatile. DuraCor has no grazing or haying restrictions for any class of livestock, including lactating dairy cows, horses (including lactating mares) and meat animals prior to slaughter. Label precautions apply to forage treated with DuraCor and to manure and urine from animals that have consumed treated forage. Consult the label for full details. Always read and follow label directions.
