Crabgrass

INTRODUCTION

Crabgrasses (Digitaria spp. ), the first cultivated grains, were grown for food thousands of years before they were considered weeds. Digitaria, a genus of about 60 species, grows in the world's temperate and tropical regions. Many of the species are good forage grasses. Thirteen weedy Digitaria species infest the United States, but large crabgrass (D. sanguinalis #3 DIGSA) and smooth crabgrass (D. iscbaemum # DIGIS) are the most common. The seeds are very nutritious.Stone Age lake dwellers in Switzerland cultivated crabgrass; "foxtail millet," a form of crabgrass, was an important food crop in China in 2700 B.C.

DESCRIPTION AND USE

From prehistoric times, crabgrass has been grown for food in India and Africa. In parts of the world, some kinds of crabgrass are still important cereals, providing staple grains for porridge and bread. In 1759, Lorenz Heister (1683-1758) named the genus from digitus, Latin for finger, referring to the plant's digitate inflorescence. D. sanguinalis Scop. was described in 1772 by Giovanni Antonio [Johann Anton] Scopoli (1723-1788); Johann Christian Daniel von Schreber (1739-1810) de-scribed and Gotthilf Henry Ernst Muhlenberg (1753-1815) reclassified D. iscbaemum (Schreb. ) Muhl. in 1804 and 1817, respectively. The name sanguinalis refers to the plant's blood-red or purple color and iscbaemum to the arrangement of the plant's seeds along the spike midriff.

Large crabgrass usually has gray-green, some-times green, foliage and dense, coarse hair. Its racemes are 5 to 15 cm long centered in a terminal whorl (sometimes with an additional whorl below). Smooth crabgrass is essentially hairless, with foliage varying from yellow-green to blue-green to reddish in old plants. Its racemes are 4 to 10 cm long and scattered rather than centered in a terminal whorl. The United States Patent Office introduced large crabgrass into this country as a forage crop in 1849, a time when livestock numbers were increasing rapidly and good forage was scarce. The Department of Agriculture, founded in 1862, later assumed plant introductions. But without demonstrations and promotional information, crabgrass generated little interest and soon became a forgotten crop. However, decades later when southern ranchers sought a good forage grass for the expanding cattle business, they found large crabgrass perfectly suited because of its affinity for hot, dry conditions and its nutritious qualities as pasture and hay.

ORIGINS AND DISTRIBUTION

Immigrants from Poland and central Europe in the late 19th century and early 20th century brought crop and garden seeds, including crabgrass, with them. They held the crop in high esteem, calling it "manna grits." A form of millet native to central Europe, crabgrass thrived in many soil types, grew and matured rapidly, and produced abundant yields, making it a reliable crop. Immigrant farmers eventually abandoned crabgrass in favor of wheat (Triticum aestivum L.) and corn (Zea mays L.) which were more profitable and easier to grow. However, characteristics which once made crab-grass a valued crop now make it a pernicious weed. A large crabgrass plant can produce 700 tillers and 150,000 seeds in temperate areas like the United States and even greater numbers of seeds in tropical climates, where it grows as a perennial and flowers all year. The plant escaped to fields, roadsides, and wastelands and ultimately spread to every state; it is one of the nation's major lawn weeds.

Large crabgrass is troublesome in temperate and tropical crops. Its latitudinal range extends from 50 N to 40 S. Because of its ability to adjust to tropical and temperate conditions, it is reported as a weed in 33 crops in 56 countries. In the United States, large crabgrass is one of the three most serious weeds in peanuts (Aracbis bypogaea L.), and it is a principal weed of sugarcane (Saccbarum o fficinarum L.), cotton (Gossypium birsutum L.), and sorghum [Sorghum bicolor (L.) Moench. ] . Crabgrass is a weed in orchards, vineyards, and their crops. It is found among shrubs or ground cover in ornamental planting and along roads and ditches. The plant reproduces by seed, but roots at the nodes to form mats in moist soils. It is a serious weed of lawns, because the stems are usually prostrate and below the mower blade. The rapidly growing seedlings soon crowd out pre-ferred finer-leaved grass species. Mats of broad-leaved, gray-green grass spot the lawn and turnbrown after the first frost. Ada George wrote in 1914, "The seeds of this grass must be very long-lived, for, though it is never sown, let the ground be cultivated, and as a general thing Crab-grass will be there."

LITERATURE CITED

1. Hitchcock, A. S. 1950. Manual of the Grasses of the United States. U.S. Govt. Print. Off., Washington, DC. Second ed. rev. by A. Chase.

2. Holm, L. G., D. L. Plucknett, J. V. Pancho, and J. P. Herberger. The World's Worst Weeds. Univ. Press Hawaii, Honolulu.

3. Georgia, A. 1914. Manual of Weeds. The Macmillan Company, New York.

4. U.S. Dep. Agric. 1970. Selected Weeds of the United States. Ag. Handbook No. 366. Washington, DC.