Latin: Polygonum aviculare

Other names: Birdweed, pigweed

Family: Polygonaceae

Knotgrass, common in the UK and Ireland, belongs to the buckwheat family (Polygonaceae). It is also known as birdweed or pigweed. This weed can be identified by its prostrate growth habit, slender stems, and small pink or greenish flowers.

Knotgrass is an annual or perennial plant that typically grows close to the ground, forming dense mats.

Identifying Knotgrass

Knotgrass early growth

The leaves of knotgrass are alternate, narrow, and lanceolate in shape. They are usually blue-green in color and have a pointed tip. The stems are slender, often reddish, and have swollen nodes.

The flowers of knotgrass are small and inconspicuous, clustered in the leaf axils. They can vary in color, ranging from pink to greenish. The flowers bloom from spring to autumn, depending on the species and environmental conditions.


The Challenges of Knotgrass

Knotgrass’ prostrate growth habit allows it to spread rapidly and form dense mats, outcompeting desired plants for resources such as nutrients, water, and sunlight. 

Due to the way in which Knotgrass grows it can cause more prominent issues in spring sown crops versus winter crops. Knotgrass can also interfere with the establishment and growth of turfgrass in lawns.

One of the challenges with knotgrass is its ability to produce abundant seeds that can remain viable in the soil for several years. These seeds can germinate and establish new infestations, leading to ongoing weed management efforts.

Nufarm products to help with your Agronomy recommendations: