from the Latinword for blood, which refers to the plant's often reddish-purple inflorescence. Teischaemum part of the name originates from the Greekwords "ischo" (to restrain) and "haima" (blood), which refers to an herb used in ancient times to stop bleeding; however, again it probably refers to the reddish-purple inflorescence.
Smooth crabgrass is written botanically as Digitaria ischaemum (Schreb.) Schreb. ex Muhl. “Schreb.” refers to Johann Christian Daniel von Schreber (1739-1810), a German naturalist. Gotthilf Heinrich Ernst Muhlenberg (1753-1815) was a botanist and an American clergyman from Trappe, PA (located near Philadelphia, PA). In botanical authority nomenclature, the "ex." indicates the plant was initially described by one author, but later a second author re-classified the plant. Terefore, Schreber first described smooth crabgrass, but Muhlenberg later re-described it according to valid, or currently accepted, botanical methods. Incidentally, Muhlenberg’s grave is located in Lancaster County, PA, in the same cemetery as President James Buchanan.
Large crabgrass and smooth crabgrass are very similar in appearance. Large crabgrass has a hairy stem and leaves (A); smooth crabgrass has a few hairs at the collar region near the membranous ligule (B); both are considered opportunistic weeds and will germinate in bare soil (C) and thin turf (D); when crabgrass begins to tiller they often form “clumps” (E); and can spread from stolons (F). Source:
https://turf.purdue.edu/crabgrass/
Large crabgrass is written botanically as Digitaria sanguinalis (L.) Scop., where Digitaria is the genus, and sanguinalis is the specific epithet, which distinguishes the plant from others within the same genus. Te two names together—genus and specific epithet—refer to the species.
Next, the “(L.) Scop.” is the authority (the person or persons that first described the species). Te “L.” refers to Carl Linnaeus (1707-1778), the famous Swedish taxonomist. Te “Scop.” name refers to Giovanni Antonio Scopoli (1723-1788). He was an Italian physician and also a naturalist, and was often called the “Linnaeus of the Austrian Empire.” Scopoli frequently corresponded with Linnaeus about his research and plant descriptions, and Linnaeus had a great deal of respect for Scopoli. However, the two never met in person, most likely due to the geographical distance between them and the travel challenges at the time.
Crabgrass germinates and emerges in the spring, grows slowly at first, but then becomes aggressive and invasive later in the summer, and then finally produces seeds (inflorescence) by late summer. Crabgrass is a warm- season weed that can thrive at the time when cool-season turfgrasses are at their weakest. For example, in lawns with cool-season turfgrass species, such as Kentucky bluegrass (Poa pratensis), crabgrass gains that competitive advantage during the summer months when Kentucky bluegrass growth has slowed. In the U.S. Mid-Atlantic region, crabgrass leaves are often observed emerging above the lawn canopy by the first week of July. When those crabgrass plants tiller, they will expand into the turf and leave large voids after they seed and then die at the first frost. Crabgrass has very shallow roots because, as an annual plant, it wants to send all its carbohydrates toward seed production at the expense of roots and shoots.
Crabgrass can be a persistent weed where the turfgrass is weakened and becomes noncompetitive due to many circumstances: mowing too low; under fertilized; thinned from diseases or insect pests; thinned due to unfavorable growing conditions (i.e., hot, humid weather); next to sidewalks and other areas with thin turf or shallow soil; trying to establish turf in the summer; and winter annual weeds die and thus leave voids for crabgrass to germinate and grow.
Crabgrass management starts with proper cultural practices, such as a higher mowing height and proper fertilization, to give turfgrass that competitive advantage. Today, many preemergence and postemergence herbicides are available to effectively manage crabgrass in turfgrass.
Sources: Elmore, M.T., Patton, A.J., Gannon, T.W., and Brosnan, J.T. 2023. Advances in turfgrass management. p. 339-388. In: Fidanza, M. (Ed.), Achieving sustainable turfgrass management. Burleigh Dodds Science Publishing; Cambridge, UK. Mathias, K. 2025. Major pests and control programs for the Maryland turfgrass industry in 2023, part 3: Sod production. MTC Turf News, Spring 2025 edition, p. 12-14.
Mike Fidanza, Ph.D., is a professor of Plant and Soil Science at Pennsylvania State University, Berks Campus, Reading, PA. Cale Bigelow, Ph.D., is a professor of Turfgrass Science and Ecology in the Department of Horticulture and Landscape Architecture at Purdue University, West Lafayette, IN. They are teaming to provide a Rooted in Research article for each issue of Turf News.
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