Prostrate Knotweed

Weeds

knotweed, knot-grass, ninety-knot, bird's-tongue, cow-grass, goose-grass, stone-grass, pink-weed, mat-grass, door-weed, bird-grass, way-grass

Polygonum aviculare

Photos

Prostrate knotweed is a supreme indicator weed. Knotweed is the earliest germinating of all the summer annual weeds. Due to its early germination timing, knotweed is able to claim resources and invade damaged areas before other desirable grasses begin to grow. Prostrate knotweed is commonly associated with soil compaction and can be seen in gravel roadbeds, sidewalk edges, crevices, paths and other high-traffic areas (like in front of soccer goals). When knotweed germinates in March is often resembles grass and can offer some false hope that those damaged areas are spontaneously repairing themselves where the snowplow missed the sidewalk. The root system of prostrate knotweed is extremely fine and can mine even the most compacted soils. Prostrate knotweed produces very diminutive pinkish-white flowers in the axils of the leaves and reproduces by seed. Once established, knotweed is very difficult to remove with most herbicides.

Crops Affected: turf

Management

As the poster child indicator weed, prostrate knotweed should always sound the alarm to look for soil compaction. Damaged areas will often 'spontaneously recover' in the spring only to later turn out to be knotweed. Relieving soil compaction is the key to improving turf vigor and limiting future populations of prostrate knotweed. It may also be prudent to protect areas along driveways and sidewalks with reflectors in the winter time (or stop using a 10-foot snow plow on an 8-foot sidewalk). Turf managers may want to consider using ropes, gates, or other methods of re-directing traffic in problem areas.

Similar Species

Prostrate knotweed can be casually confused with spotted (prostrate) spurge or common purslane. The leaves of purslane are very thick and shiny compared with the dull blue-green color of knotweed. Purslane also has red stems. Spotted spurge also forms mats, however, the leaves, stems and roots of spotted spurge will exude a milky white latex when damaged.

MSU Extension Turf