This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Introduced. Perennial. Propagates by seeds and by tuber-bearing rootstocks.
Time of bloom: July to September.
Seed-time: August to November.
Range: Virginia to Kansas, southward to Florida and Texas.
Habitat: All soils; troublesome in cultivated crops, especially in cotton fields.
This pest is said to have been brought into the United States among some garden plants from the West Indies, nearly a century ago, since when it has spread over a very large part of the country where the climate is propitious to it, extending along the coast as far north as New Jersey. It is very difficult to dislodge, experience having shown that "nothing serves so well to propagate it as to plow and replow, with a view to destroy it," as a planter stated in a letter to Dr. Darlington. The smaller tubers are sometimes shipped, clinging to the roots of garden plants and nursery stock, and the seeds are a common impurity of southern grass and clover seed and baled hay; they are hard-coated and pass unharmed through the digestive tracts of cattle and horses, and such manure, without long composting, is a menace to the land where it is spread. (Fig. 34.)
The fibrous, scaly rootstocks, which are its most mischievous part, are deep-set, first forming by descending from the base of a young plant, to a depth of six inches to a foot or more according to the mellowness of the soil, and there forming the first small, round, potato-like tuber, varying from the size of a pea to three-fourths of an inch in diameter; from this center, horizontal cord-like rootstocks are extended in every direction, producing new tubers at intervals of two to ten or more inches, which immediately send up shoots to the surface and begin to throw out their own lateral growths; and so on, indefinitely, provided that the food-producing leaf-growth above is permitted to flourish. The leaves appear first in the spring, three to six inches long, one-eighth to one-fourth inch wide, rather thick, smooth, with mid-vein prominent below and forming a slight channel above. Culm slender, smooth, three-sided, six to eighteen inches tall, leafless except for three or four involucral bracts at its summit, one to four inches long and subtending the umbellate cluster of flowers. Rays of the umbel two or three inches long, spreading, bearing on the upper part four to nine flowering spikes with twelve to forty spikelets; scales closely imbricated, ovate, pointed, dark purplish brown with a green' keel and margin; stamens three and style three-cleft, exserted much beyond the tops of the scales. The many small achenes are oblong, pointed at both ends, three-sided, dull green or brown.
Fig. 34. - Nut-grass (Cyperus rotundus). X 1/4.
Prevent seed production. Although the weed is very prolific, both above and below ground, the growth of flowering stalks is most exhaustive to the underground tubers, and if such stalks are persistently hoe-cut, before the flowers mature and sow their progeny, the tubers in the soil must gradually yield up their life. Both dormant seeds and tubers should be stimulated to active growth by frequent stirring of the soil in the fore part of the season, but the main battle should come at the time when the plant is expending all its resources, above and below, in the development of seed, which must not be permitted to come to perfection. This intensive, late cultivation should be followed by heavily seeding the ground to some winter crop, such as Rye or Winter Vetch or Japan Clover, to be used for winter grazing which will keep down the Sedge; the crop to be plowed under in the spring for green manure.
Care should be taken that the rootstocks and small tubers are not transported to clean land on farm implements.