Weed Science - Weed ID

Soil and Crop Science 4250 Crow

Quackgrass

A cool-season perennial grass that spreads by seeds and rhizomes; key ID features include a membranous short ligule; leaf blade is flat, dull green to light blue, tapering to a point, sparsely hairy with a coarse texture; sheath may be hairy or smooth; auricles are claw-like and clasp the stem.

Johnsongrass

A large, upright perennial grass up to 6–7 ft tall; spreads by seeds and rhizomes; ligule short-membranous with fringe of hair at the top; leaf blade coarse with a white midrib, 12–30 inches long, hairless with smooth edges; sheath open, hairless to sparse; auricles absent; multiple tillers.

Hoary cress

An upright perennial forb about 2–3 ft tall; reproduces by seeds and rhizomes; leaves alternately arranged, blue-green and lance-shaped (lower leaves stalked, upper leaves sessile); 2 lobes clasping the stem; margins irregularly toothed to smooth; flowers in somewhat flat-topped clusters with 4 petals per flower; seedpods resemble bladders.

Leafy spurge

Upright perennial up to 4 ft tall; reproduces by seed and rhizomes; leaves are simple, opposite, blue-grey; cut stems exude milky sap that can blister skin; distinctive greenish-yellow flower bracts.

Field bindweed

Herbaceous perennial with creeping stems and rhizomes; leaves alternate, shovel-shaped with pointed or blunt lobes at the base; stems can reach up to 6.5 ft; flowers are bell/funnel-shaped, white to pink, about 1 inch in diameter, with two small bracts located about 1 inch below the flower.

Dodder

Annual parasitic vine with thin thread-like stems that are yellow to orange; flowers are small and white and bell-shaped.

Canada thistle

Aggressive perennial 2–5 ft tall with creeping rhizomes; leaves alternate, lance-shaped with irregular lobes and wavy, spiny or toothed margins; stems usually smooth with occasional short hairs or grooves; flowers are purple/pink/white at ends of stems in clusters about ½ inch wide by ¾ inch long.

Russian knapweed

Persistent perennial up to 3 ft with creeping rhizomes (black and scaly); limited seed distribution; leaves alternate, irregularly notched, oblong to linear-lanceolate; upper leaves smaller up the stem; stems extensively branched, young stems canescent; flowers solitary on branch ends, pink/purple turning straw-colored at maturity.

Perennial sowthistle

Upright, deep-rooted perennial up to 6 ft; reproduces by seed; leaves alternate with prickly edges and pointed lobes, becoming smaller toward the top; stems hollow and branched only at the top and contain milky juice; flowers bright yellow about 1.5 inches wide; bracts at the base green, bristly, with sticky hairs.

Jointed goatgrass

Winter annual grass up to 2.5 ft tall; reproduces by seed; ligule present (unspecified in notes); leaf blade alternating with long hairs on margins, about 1/8–1/4 inch wide; sheath with long hairs; stems hollow; spikes cylindrical and narrow; auricles not present.

Ligule (vocabulary term)

A membranous or hairy appendage located at the junction between the leaf blade and sheath in grasses; an important ID feature for distinguishing grass species.

Rhizome (vocabulary term)

A horizontal underground stem that can produce new shoots and roots, enabling plants like many weeds to spread vegetatively.