Narrowleaf hawksbeard (Crepis tectorum)- August 2019
(By Shelley Mills, Valley County Extension Ag Agent, email@example.com)
Narrowleaf hawksbeard (Crepis tectorum L.), also known as narrowleaved hawk’s beard is a facultative winter annual native to Siberia. It was first identified in North America as early as 1890 when it was found in a ballast heap in Newfoundland. It was also introduced to Alaska in the 1970’s through unknown means but likely shipping of goods from Russia. Hawksbeard is NOT a noxious weed in Montana at this time, however it is considered a noxious weed in Alaska and Minnesota in the United States, and Alberta and Manitoba in Canada.
Identification and biology
Narrowleaf hawksbeard is a member of the Asteraceae family, the same family containing dandelions, Canada thistle, knapweed, yellow starthistle and several other noxious weeds in Montana. Hawksbeard grows from a shallow taproot. Height ranges from 10cm (4 in) to nearly 100 cm (40 in). Basal leaves, which may be undeveloped, are petiolate, toothed or lobed pointing toward the crown, while stem leaves are narrow, sessile and entire, and less than 1 cm wide. All parts of the plant exude a milky sap when broken. Two peak flowering periods occur annually in Montana, late June through July and September through October, but it has been known to flower throughout the summer when conditions are favorable. Five to 20 showy, yellow, flower heads at the end of stems are composed of 30 to 70 petals arranged in a ray pattern.
Habitat and spread
Hawksbeard is highly adaptive and has become an established weed in range, pasture, Conservation Reserve Program (CRP) acres, waste areas roadsides and cropland. Hawksbeard reproduces solely by seeds that are structurally like dandelion seeds; the pappus allows the seed to be readily dispersed via wind, water, animals, and humans. Each plant will produce between 3,000 and 49,000 seeds.
Hawksbeard is competitive with small grain and pulse crops, resulting in significant yield reductions. A study of cropland in Daniels County, Montana, revealed nearly 100% yield loss of wheat in plots where hawksbeard was not managed. Hawksbeard will readily invade any area with disturbed soil, but will also infest well-managed range, pasture, grasslands and other established crops.
In cropland applications of herbicides early in the year as a pre-plant burndown and a fall application of plant burndown are critical for managing this facultative annual. Management of the weed while in the rosette stage is critical. In-crop herbicide applications are complicated by crop species, and care must be taken to ensure that herbicides used are in accordance with crop rotation strategies. In range, pasture and CRP, applications in very early spring before alfalfa breaks dormancy combined with late fall applications after alfalfa goes dormant of one pint of 2,4-D have been effective as well as applications of metsulfuron methyl. Always read and follow label directions. If you have a smaller infestation of hawksbeard, hand pulling or digging will work, but flowering plants need to be bagged and removed to avoid seed set and dispersal. There are no approved biological control agents in the United States for hawksbeard. A fact sheet regarding narrowleaf hawksbeard management will be forthcoming.