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Weed Identification in Christmas Trees

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Spotted knapweed - Centaurea stoebe L. ssp. micranthos
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Spotted knapweed stem
Spotted knapweed stem.

Life cycle: Biennial or short-lived perennial.

Leaves: First-year leaves originate from a basal rosette, followed by a flowering stem in the second year. Basal leaves are deeply and irregularly lobed on long stalks; stem leaves are alternate and finely dissected. Leaves are grayish green and roughly hairy.

Stems: Erect, wiry stems elongate during the second year, up to 6 feet tall with multiple branching. Stems are roughly hairy and often green to purple-striped.

Flowers and fruit: Terminal and axillary heads consist of purple to pink disk flowers above encircled by distinctly black-tipped bracts below. The seed is enclosed in a single-seeded, olive-green to brown fruit with a bristly pappus that can attach to animals for transport.

Reproduction: Seeds.
Spotted knapweed rosette Spotted knapweed leaf Spotted knapweed flower
Spotted knapweed rosette. Spotted knapweed upper leaf. Spotted knapweed flower head.
The MSU IPM Program maintains this site as an access point to pest management information at MSU. The IPM Program is administered within the Department of Entomology, fueled by research from the Michigan Agricultural Experiment Station, delivered to citizens through MSU Extension, and proud to be a part of Project GREEEN.
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02/08/08