This guide includes photos and characteristics to help you identify the annual grass weeds common to Minnesota.
General characteristics
Any or all of these vegetative characteristics may be useful in identifying a young grass weed.
Leaves
They usually have long, narrow, alternate leaves with parallel venation (the distribution or arrangement of veins), an expanded leaf blade portion and a leaf sheath portion toward the base that encircles the stem.
Most have a projection at the base of the leaf blade called a ligule, which may be a membrane, a fringe of hairs or a combination of both.
Some have claw-like or hook-like projections at the leaf collar called auricles that may partially encircle the stem. The collar area is the juncture of the leaf blade with the leaf sheath.
As grass leaves emerge from the bud shoot, they may be rolled (round) and overlapping or flat and folded (V-like).
Leaf sheaths may be open and overlapping, or they may be closed.
Seeds
The seed often remains attached to the primary root after germination.
If you carefully remove the grass seedling from the soil, the seed may help identify the plant.
Other plant characteristics
Have definite nodes (swollen ridges that encircle the stem) and internodes (portions of the stem area between nodes).
Stems (culms) may be round or flattened.
May be smooth (glabrous) or hairy.
These plants are monocots that have one cotyledon or seed-leaf that remains in the soil after seed germination.
Annual grass weeds
Echinochloa crus-galli (L.) Beauv.
Vegetative characteristics
Leaf blade: Smooth and mostly hairless leaf blades. Keeled below.
Leaf sheath: Smooth, open, flattened and keeled.
Collar: Broad, smooth and yellowish-green. Continuous (not divided by midvein).
Ligule: None
Auricles: None
Flowering characteristics
Inflorescence: Raceme-like panicle
Spikelets: Bristly, hairy
Digitaria sanguinalis
Vegetative characteristics
Leaf blade: Densely hairy on both surfaces. Keeled below.
Leaf sheath: Open and densely hairy.
Collar: Broad and divided by midvein. Hairy on outside edges.
Ligule: Membranous and prominent. Rounded to acute with wavy-edged margin.
Auricles: None.
Flowering characteristics
Inflorescence: Digitate (finger-like) panicle.
Spikelets: Pressed closely against the panicle.
Setaria viridis (L.) Beauv.
Vegetative characteristics
Leaf blade: Leaf blades are relatively free of hairs on both upper and lower surfaces.
Leaf sheath: Hairy and open, with overlapping margins and stiff, bristle-like hairs on outer margins.
Leaf collar: Continuous.
Ligule: Fringe of hairs approximately 0.5 millimeters long.
Auricles: None
Flowering characteristics
Inflorescence: Cylindrical head (compact panicle) about 3 to 4 inches long. Droops or nods from the tip.
Spikelets: Crowded, subtended by two to three bristles that arise from the base of the spikelet.
Setaria faberi
Vegetative characteristics
Leaf blade: Dense covering of hairs on the leaf blade’s upper surface, and few scattered hairs on the lower surface.
Leaf sheath: Hairy, slightly flattened and keeled (ridged at mid-vein). Open with stiff, bristle-like hairs on margins.
Collar: Continuous.
Ligule: Fringe of hairs 1-2 mm long. Longer hairs at collar margin.
Auricles: None
Flowering characteristics
Inflorescence: Cylindrical head (compact panicle) about 3 to 5 inches long. Droops from the base.
Spikelets: Crowded, subtended by numerous bristles (usually three to six) that arise from the base of the spikelet.
Setaria pumila
Vegetative characteristics
Leaf blade: Smooth, except for several prominent whitish hairs near the base on the upper surface.
Leaf sheath: Smooth, flattened and sharply keeled.
Collar: Smooth and continuous.
Ligule: Fringe of hairs.
Auricles: None
Flowering characteristics
Inflorescence: Short, narrow, cylindrical head 2 to 3 inches long (compact panicle).
Spikelets: Crowded, subtended by three to six yellow bristles that arise from the base.
Seeds are larger than those of giant or green foxtail.
Avena fatua
Vegetative characteristics
Leaf blade: Smooth and usually hairless, with the exception of stiff, bristle-like hairs along the lower edge.
Leaf sheath: Open, round and often pubescent, with overlapping margins.
Collar: Broad and smooth.
Ligule: Membranous and prominent.
Auricles: None
Flowering characteristics
Inflorescence: Spreading, true panicle.
Spikelets: Have two large glumes (chaffy bracts) that enclose two to three seeds. Seeds (grains) are hairy toward the base with bent and twisted awns.
Panicum dichotomiflorum Michx.
Vegetative characteristics
- Leaf blade: Seedlings have hairs on the lower leaf surfaces that disappear as the plant matures. Leaf blades of mature plants are hairless, often glossy-appearing, and have a distinct white midvein.
- Leaf sheath: Open, round, smooth, and hairless.
- Ligule: Fringe of hairs that’s 2 to 3 millimeters long.
- Auricles: None.
- Stems: Prominent nodes that are bent in different directions, giving the plant a zigzag appearance.
Flowering characteristics
- Inflorescence: Spreading panicle. Culms often have several panicles arising from lower-leaf sheaths. These frequently don’t fully extend from the boot.
- Spikelets: Small with three apparent glumes; the first is short and blunt.
Panicum miliaceum L.
Vegetative characteristics
Leaf blade: Wide and with long hairs on both sides.
Leaf sheath: Open, round, prominently veined, and coarsely hairy.
Ligule: Fringe of hairs.
Auricles: None
Flowering characteristics
Inflorescence: Spreading panicle that’s 6 to 12 inches wide.
Spikelets: Large (1/16 inch across) with three apparent chaffy glumes; the first is half-length and pointed at the tip. Seeds are olive-green to black and shiny.
Reviewed in 2022