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Knotweed flowers around stemPlant Description: Knotweed is an erect, broad-leaved, semi-woody perennial that spreads by long rhizomes and occasionally by seeds. The plant forms dense clumps that exclude other plants, and radiates rapidly to form patches that can be as large as 1 to 3 acres. It is one of the most persistent, and hardy of weeds, and it tolerates many control measures. Knotweed is an invasive plant that can overrun natural areas, gardens, yards, roadsides, and utility and railroad rights-of-way. The root system is fibrous, but rhizomes are white when young, becoming brown, thick, and woody with age. Young shoots are reddish, with mostly heart-shaped leaves. Stems are erect, tall (up to 10 or more feet for mature stands), and hollow except at the prominent, swollen, knot-like nodes. Leaves are alternate (one per node), broad, flat to round at the base, tapering to a pointed tip, and attached by long petioles. The upper leaf surface is dark green and the lower surface is pale green. Small, greenish white flowers are clustered along branching panicles arising from upper leaf axils. Plants are unisexual, with male and female flowers on separate plants. Male flower stalks are mostly erect and female flower stalks are drooping. When blooming (July to September), the plant puts on an attractive floral display befitting the common name 'fleece flower'.

Knotweed seedlingKnotweed shoots resume growth in early spring, reaching a fast pace (reportedly 2 to 4 inches in a single day) and attaining heights over 10 ft by late summer. Plants form dense colonies, spreading by rhizomes that can extend up to 65 feet. New colonies can regenerate from as little as a 1-inch piece of rhizome, which can easily be transported wherever soil is moved. Rhizomes send out shoots from April to August, even from a depth of over 3 feet. Knotweed exhibits great tolerance to most herbicides. It is reported to be a poor invader into grass cover and can be crowded out by taller trees. It does not survive frequent mowing.