Polygonum aviculare - Prostrate knotweed

Polygonaceae


Prostrate knotweed is a summer annual that spreads by seed. It is one of the most common weeds in Oregon production fields, and is one of the most difficult to control.

Seedlings germinate in mid to early April (in Oregon’s north Willamette Valley). Preemergence herbicides should be applied prior to emergence. Postemergence control is difficult with herbicides.

Prostrate knotweed grows flat along the soil surface, with little or no vertical growth. Plants form circular mats up to 30 inches in diameter.

Plants form thick mats that aggressively compete with plants.

Flowers occur in axillary clusters, but are generally too small to see with the naked eye.

Flowers have no petals (plants in this family are apetalous, without petals). Pink color on these flowers are sepals, not petals.

Foliage is linear to elliptical in shape. Foliage size varies, probably depending on available moisture.

A major identifying characteristic of this weed is a structure called the ocrea, a membranous sheath that forms around the stem at each node.

The ocrea is a characteristic of virtually all plants in this family.


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