Common knotgrass – Polygonum aviculare

Polygonum aviculare

Polygonum aviculare

Polygonum aviculare (common knotgrass) is an annual, seed reproducing weed. It is a nondemanding plant, with a spindly root that is very different (as habitat and leaf shape) from one year to another.

It can grow on all soil types.

Common names: common knotgrass, prostrate knotweed, birdweed, pigweed and lowgrass.


The stem is usually laid on the soil, with many branches. It has leaves from the knot area up to the tip of the plant. The length of the stem can be up to 50 cm.

Polygonum aviculare - plant

The cotyledons are very long, uniformly wide and with rounded tips.

Polygonum aviculare - cotyledon

The real leaves are elliptical, or lanceolate to linear, with pinnate veins. The leave have no petioles and are connected with a thin, leather-like tube that is split and surrounds the stem.

The flower is small, with short peduncles, pink or white-green. A bunch of 2 to 5 flowers are located on the leaf’s axilla.

Polygonum aviculare - flower

Polygonum aviculare - flower 1

The germination period is from spring until late summer. It germinates on the superior soil layer and it needs light in order to germinate.

The blossoming period is June until autumn. The plant produces between 125 to 200 seeds.

How to fight this pest plant

The herbicides that are recommended when fighting the common knotgrass are: Adengo, Buctril Universal, Cerlit, Esteron Extra, Merlin Duo.

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