Knot weed

Polygonum aviculare

Prostrate Knotweed is a summer annual, which forms dense patches. Prostrate knotweed is probably the earliest of the summer annuals to germinate in the spring. Prostrate knotweed is often confused with first-leaf crabgrass. Prostrate knotweed is a prostrate weed that produces a thin tap root and multiple branched stems. Even though knotweed does not root down at the nodes of the stems, a single plant can form a dense mass up to three feet across. Prostrate
knotweed tolerates extremely compacted soils and is often found in high traffic areas. The leaves appear alternately on the stems, and differ in the color of green depending on the age of the leaf, with older leaves being a less intense green. The stems will be knotty and have a paper like sheath.

Knotweed flourishes in compacted soils with low oxygen diffusion. Soil conditions can be made less favorable by lightening with core aeration. If possible, traffic should be re-routed to prevent future compaction.

Knotweed may be physically removed, although compact soil conditions may make complete root removal difficult.

A dense, vigorous stand of turf will help prevent knotweed infestation. Use insect and disease control programs as well as a good fertility program. However, avoid fertilizing knotweed plants until after their reproductive cycle when they\'re not as competitive.

Source:  Virginia Polytechnic Institute & State University