Weed Descriptions: Grasses and Grasslike Weeds
Crabgrass ( Digitaria spp.)
Two species of crabgrass, hairy and smooth, are commonly found in Pennsylvania (smooth crabgrass predominates in turfgrass stands). Both species are summer annuals and have wide (¼- to ½-inch), sparsely hairy, pale-green leaves that taper to a sharp point. Leaves of hairy crabgrass are hairier than smooth crabgrass. The ligules of both species are long and membranous. Crabgrass does not have auricles. Seedheads are divided spikes that project like fingers from the stem, producing thousands of seeds in late summer. Seeds germinate in spring when soil temperatures reach 55° to 58° F for several consecutive days. Crabgrass plants die after the first frost in early fall.
Goosegrass ( Eleusine indica )
Goosegrass, also known as silver crabgrass, is common in southern Pennsylvania. Leaves are darker green and narrower than crabgrass (1/8 to ¼ inch) and sheaths have a silvery-green color (especially near the center of the plant). The ligule of goosegrass is membranous and divided in the center. The collar region is sparsely hairy and has no auricles. Goosegrass has a divided spiketype seedhead bearing seeds in straight rows on the seed stalks. Goosegrass seeds germinate four to six weeks later than crabgrass and germination continues throughout the summer.
Barnyardgrass ( Echinochloa crusgalli )
Barnyardgrass is a summer annual grass with wide (greater than ½ inch) leaves and sheaths that lie close to the ground. Barnyardgrass seeds germinate later than crabgrass seeds, and plants do not tolerate low mowing heights. This species has no ligule or auricles. The seedhead is composed of compact spikes arising at several locations on the main stalk. Barnyardgrass can be a problem in newly established turf if seed is introduced with the topsoil.
Foxtail ( Setaria spp.)
Foxtail is a light-green, leafy, summer annual grass weed that reaches maturity in midsummer. It is often confused with crabgrass. As a weed in turf, foxtail is much less common than crabgrass, but it can proliferate under low-fertility conditions and high mowing heights as well as in spring seedings. This weed can be distinguished from crabgrass by its hairy ligule and short, compact spike seedhead.
Annual bluegrass ( Poa annua )
Annual bluegrass is a light-green, small-statured, bunch-type winter annual grass. Annual bluegrass is a highly diverse species with some subspecies functioning as short-lived perennials. The ligule is long and membranous and no auricles are present. Small but conspicuous open-panicle seedheads are evident during most of the growing season. Most seeds germinate in late summer or early fall. Although this species can persist throughout the entire growing season on irrigated sites, it usually dies during hot, dry conditions if not irrigated.
Bentgrass ( Agrostis spp.)
Bentgrasses are desirable turfgrass species when used on golf course fairways, putting greens, and croquet courts. However, they are a common perennial grass weed in many home lawns. Like other stoloniferous weeds, bentgrass creeps over desirable turf and forms large light-green patches that usually turn brown in summer. Bentgrass has rolled vernation; long membranous ligules; no auricles; and narrow, flat leaf blades that have equal-sized veins across the entire width of the blade. The seedhead is an open panicle but is rarely seen in lawns.
Orchardgrass ( Dactylis glomerata )
Orchardgrass is a bunch-type perennial grass weed that forms light green clumps in lawns. Leaves have folded vernation and are wide (¼ to ½ inch), light green, and pointed at the tip. The sheaths of orchardgrass are strongly compressed and flattened. Other features of orchardgrass are the long, membranous ligule and the open-panicle seedheads.
Nimblewill ( Muhlenbergia schreberi )
Nimblewill is a blue-green perennial grass that is common in Pennsylvania lawns during summer. It spreads over existing turf by stolons and forms dense patches. Leaf blades have a medium texture (about ¼ inch wide) and are short (1 ½ to 2 inches) with leaf tips tapering to an abrupt point. The stems are long, slender, and wiry with prominent nodes. Ligules are short, membranous, and jagged. The leaf blades have long hairs at the margins but do not possess auricles. Seedheads are long, slender, and inconspicuous. Nimblewill grows rapidly during the warm summer months and turns brown or tan in winter.
Yellow nutsedge ( Cyperus esculentus )
Yellow nutsedge is not a true grass but a member of the sedge family. Plants in this family are characterized by erect, triangular stems and a preference for moist or wet areas. Leaves and stems are yellow-green and shiny. Although leaves and aboveground stems die in winter, new growth occurs in spring and summer from vigorous, scaly rhizomes and nutlets that grow underground. Chestnut-brown seedheads may be present on plants that are not mowed.
Wild garlic ( Allium vineale )
This species is a perennial weed that has a strong garlic or onionlike odor when cut. It is one of the first weeds to emerge in early spring. Wild garlic produces long, slender, mostly hollow leaves that are dark green and covered by a waxy substance. Leaves emerge from underground bulblets that are covered by thin, papery scales. Flowers may be present on uncut stems and can be white, pink, or purple.
A closely related species, wild onion ( Allium canadense ), looks very much like wild garlic. Wild garlic is more common in Pennsylvania and has hollow leaves. Wild onion has flat (not hollow) leaves. Depending on the growth stage and time of year, it may be difficult to distinguish between these two species.