Field Scabious ( Knautia arvensis (L.) Coult)
Field scabious is a biennial or herbaceous perennial forb that commonly occurs in grasslands on well-drained soils, especially those with higher calcium content. It develops from a deep, somewhat woody taproot, which contributes to its persistence once established.
During its first year of growth, field scabious forms a basal rosette. Basal leaves are large, typically 4–10 inches long, and may be lance-shaped or pinnately lobed with toothed margins. In subsequent years, the plant produces one or more erect flowering stems that reach 2–4 feet tall. Leaves occur opposite each other on the stem and decrease in size upward. Upper leaves are stalkless and pinnately divided, usually with 3–6 segments on each side and a terminal lobe. The entire plant is covered in soft hairs.
Flowering occurs from early summer through fall. Flowers are borne in dense, rounded heads at the tips of stems and may resemble individual flowers at first glance. The inflorescences are often described as pin-cushion-like and may resemble chives from a distance. Florets are typically pale lilac to light blue, though they may occasionally be white or pink, and are surrounded by green bracts.
Seeds are cylindrical, hairy, and approximately 5–6 mm long, allowing for local spread once plants are established.
Quick ID Guide
Life Cycle:
• Biennial or herbaceous perennial
• First-year basal rosette
• Second-year flowering stems
Height:
• 2–4 feet
Roots:
• Deep, woody taproot
Leaves:
• Opposite on stems
• Basal leaves are large and lobed
• Upper leaves pinnate and stalkless
• Entire plant is softly hairy
Flowers (Early Summer–Fall):
• Pale lilac to light blue
• Dense, rounded heads
• Pin-cushion appearance
Seeds:
• Cylindrical
• Hairy• 5–6 mm long
Management Options
Prevention and cultural control strategies should be prioritized whenever possible. There are currently no biological control agents available for field scabious.
Because field scabious has a taproot, small infestations can be effectively managed by hand pulling or digging, provided the entire root is removed. Gloves and long sleeves should be worn during removal, as the plant may cause skin irritation.
Mowing will not eradicate established populations, but it can be useful for reducing or preventing seed production if conducted before flowering. Do not mow once seeds are present, as this may contribute to the spread.
Larger infestations may require herbicide treatment. Spring and fall applications targeting rosettes are recommended, though treatments applied to bolting plants can also be effective. Always read and follow herbicide label directions before use. Contact Sublette County Weed & Pest with questions regarding herbicide selection, application rates, or timing.
