Description:
Description and Variation: Italian thistle is a winter annual broadleaf weed that is similar in appearance to slenderflower thistle, Carduus tenuiflorus. The plant grows up to six feet tall with spiny-winged stems. The leaves are oblanceolate to lanceolate to 15 cm long and 8 cm wide. The leaves are pinnately divided into spiny-toothed or lobed segments with the terminal spine of the segments and lobes the most prominent and rigid. The underside of leaves and stems are covered with cobwebby hairs. About one to five pinkish, cylindrical flower heads are borne in terminal clusters. The number is distinctly fewer than C. tenuiflorus. Each flower head is up to two cm in length and the bracts are hairy as in C. pycnocephalus.

• Mechanical: As an annual broadleaf species, mechanical control such as tilling or digging will kill Italian thistle. Deferring autumn grazing of sheep has been effective in reducing stand density because the thistles grow etiolated and less spiny when competing with ungrazed grasses. Then sheep will graze the thistle along with the grass.
• Biological: Two fungi have been evaluated as agents on Italian thistle. An Alternaria sp., which killed C. pycnocephalus in the cotyledon stage, was also pathogenic to slenderflower thistle. A Puccinia sp., isolated and active on C. pycnocephalus, was not active on slenderflower thistle. A biotype of Rhinocyllus conicus, a bioagent commonly used for the control of musk thistle, established readily on Italian thistle in California.
• Herbicide: MCPA is recommended for application during the seedling or rosette stage. Applications after rosettes are larger than six inches in diameter may be less effective. Other growth regulator type herbicides (2,4-D, dicamba, or picloram) and Roundup may be effective, but references are not available to substantiate this. Refer to the State Noxious Weed Control Board site

For More Information:
Detailed information about Italian Thistle is available at the Washington State Noxious Weed Control Board Web Site.