University of Maryland Extension

Japanese knotweed

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Japanese knotweed (Japanese bamboo)
Polygonum cuspidatum

Japanese bamboo
photo credit Tom Heutte, bugwood.org 

Life cycle: herbaceous perennial
Growth habit:
grows up to 10 ft. high; shrubby; leaves 6 in. long by 3 in. wide, oval with smooth margins; stems similar to bamboo, but on new foliage a membranous sheath surrounds area where stem and leaf meet; flowers small green-white in spikes along the stems; small, greenish, triangular fruits

overgrowth of Japanese knotweed
Japanese knotweed 
Photo: Jan Samanek, Phytosanitary Administration, Bugwood.org 

Reproduction: reproduces from heavy rhizomes primarily but does produce viable seeds
Conditions that favor growth:
introduced as an ornamental and escaped cultivation; common weed of moist well-drained soil
Cultural control:
dig out as much root as possible and destroy; repeatedly destroy regrowth to exhaust energy reserves; this can take several seasons to get under control

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