Field scabious or blue-button (Knautia arvensis) is a tap-rooted, perennial plant in the teasel (Dipsacaceae) family. Native to Europe, the plant was likely introduced to North America as an ornamental and is currently established in northern tier states in the U.S. and in southern Canadian provinces (Figure 1).
The invasive plant is very competitive in pastures and native grasslands, invading non-disturbed rangeland, prairies, pastureland, and natural areas, as well as roadsides and disturbed sites. Once established, field scabious forms dense patches that compete with desirable grasses decreasing species diversity, hay quality and quantity, and forage for livestock and wildlife.
Field scabious grows from 2 to 4 feet in height with a long taproot. Stem leaves are opposite, deeply lobed, attached directly to the stem, and decrease in size on upper parts of the stem (Figure 2). Both leaves and stems are covered in stiff hairs. A single violet-blue to pale-purple flower occurs at the end of stems. There are 8 to 12 sepals and a ring of narrow, green bracts at the base of the flower. Once flowering is completed, the domed seed head is covered with short, bristly hairs. One plant can produce up to 2,000 seeds, which may remain viable in the soil for many years. Seeds contain an oil-rich body (elaiosome) that attracts ants, which act as dispersal agents. Animals, vehicles, contaminated soil and equipment also disperse seeds.
Field scabious is difficult to eradicate because of high seed production, difficulty in treating low-growing rosettes, longevity of seed in soil, and a deep, branching taproot. Preventing the introduction of seed is critical to stopping spread. Increasing the competitive ability of desirable grasses through well-managed grazing programs will help reduce invasion. Other prevention measures that include reseeding disturbed sites and cleaning equipment prior to moving to non-infested lands will help prevent field scabious introduction and seedling establishment.
Herbicides: Several operational programs to control field scabious are on-going in western states and southern Canadian provinces. Margie Edsall, Weed Superintendent, reports about 6,000 acres infested with field scabious in Madison County, Montana. “We apply Milestone® herbicide at 7 fluid ounces per acre (fl oz/A) and get 80+ percent control the year following treatment,” Edsall explains. “Monitoring and retreatment is needed, but some sites have been scabious-free for several years. We continue to monitor these areas because of the long seed life in soil.” Mike Jones, Gallatin County Weed District uses a tank mix of Milestone at 6 fl oz/A, plus metsulfuron at 1 ounce product/A (oz/A), plus 2,4-D at 1 quart/A and reports good control of field scabious on roadsides. Opensight® herbicide is effective on plants in the teasel family and should provide good control of field scabious at 3 to 3.3 oz/A.
Manual/Cultural: Hand pulling or digging young, newly established plants is effective if the entire root is removed. Field scabious may re-infest the area from seed or from roots left in the ground, thus long-term monitoring is needed. Maintaining healthy populations of desirable perennial grasses can minimize field scabious establishment.
Mowing: Mowing field scabious before seeds are mature (bud to early bloom growth stage) will reduce seed production but will not control the plant. Regrowth may occur and multiple mowing events may be needed to stop seed production.
Cultivation: Field scabious does not tolerate cultivation and the plant is not generally reported as a problem in cultivated fields.
Grazing: Cattle will eat field scabious prior to the plant sending up a flowering stalk. Proper grazing management that maintains forage in a healthy, competitive condition will also help to prevent the establishment and spread of this plant.
Biological Control: No biological agents are available to control the plant.
Field scabious has been studied for pharmacological and therapeutic effects, and found to include both tannins and bitter agents. Herbal tea made from the entire plant is reportedly used as a diuretic, astringent and for healing. It is applied externally to the skin in the form of herbal tea and in the form of ointment for treatment of chronic skin diseases, eczema, wounds, burns, ulcers and bruises. In homeopathy it is recommended against dry and productive cough.
Field Scabious (Knautia arvensis). Alberta Agriculture. Online http://www.agric.gov.ab.ca/app107/loadPest?action=display&id=74
Field Scabious (Knautia arvensis). Montana State University Monthly Weed Post. Online http://msuinvasiveplants.org/documents/extension/weed_posts/2014/November_field_scabious.pdf
Knutia arvensis, Invasive plant atlas of the United States. Online https://www.invasiveplantatlas.org/subject.html?sub=14662
Knautia arvensis. University of Ioannina School of Health Sci. Dept of Pharmacology, Greece. Online http://mediplantepirus.med.uoi.gr/pharmacology_en/plant_details.php?id=283
USDA, NRCS. 2019. The PLANTS Database (http://plants.usda.gov, 17 July 2019). National Plant Data Team, Greensboro, NC 27401-4901 USA.
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