Field scabious (Knautia arvensis) is also known as blue buttons and pincushion. It is thought to have come to North America as an ornamental. Native alternatives to field scabious are nodding onion, common harebell, and bluehead gilia.
Field scabious is a perennial forb. It has a flower head like a clover. The flowers are a violet-blue to pale purple almost pink. The flower heads are 1.5-4 cm wide and they grow on the ends of long leafless stalks. Field scabious grows up to 1.5 m tall. It has a taproot and the stems and leaves are covered with short, stiff hairs. One plant can produce up to 2,000 seeds. The seeds will remain viable in the soil for many years. The seeds are 5-6mm long and are very hairy. The leaves are hairy and lobed but how lobed they are varies widely from plant to plant. Stem leaves are opposite and attached directly to the stem. Lower leaves are usually somewhere between 10-25 cm long and they become smaller higher up the stem.
Field scabious is designated as Regional Noxious in the RDKB which means that if you have this plant on your property you must control it. Fortunately, there are only a couple sites of field scabious in the Boundary and they are being treated. If you see this plant please report it.
Field scabious can be found along roadsides and in disturbed areas but it has the ability to infest undisturbed pasture areas too. Once you have it it’s very hard to get rid of. Selective herbicide is an effective way to control field scabious but you need to treat for multiple years. Preventing seed production is very important. You can treat it manually by dead-heading and bagging the flowers then dig out as much of the root as possible. If it is in a field you can disk it under if it doesn’t have flowers on it. It is very important to maintain a vigorous perennial plant community. Reseed any disturbed areas and don’t overgraze. There are no biological controls available at this time.
For more information on invasive plants you can contact the Boundary Invasive Species Society on Facebook, www.boundaryinvasives.com, info@boundayinvasives.com and 250-446-2232.
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