Knotgrass

Botanical name – Polygonum aviculare

Family – Polygonaceae

Aliases – Common knotgrass, knotweed, matgrass, doorweed, birdweed, pigweed, wireweed

Knotgrass general information

Knotgrass

Knotgrass can occasionally find its way into turf, but it is generally confined to waste or unmanaged areas of grassland

Knotgrass is an annual weed that is related to the Dock family of plants. It is primarily found on waste sites and grassy areas, such as pastures, roadside verges and occasionally in lawns and managed turf. Although it will grow in most types of soil, it is particularly troublesome on light, sandy sites.

When left to grow freely the semi erect stems can reach a height of 50 – 60cm, however in closely mown turf it takes on a prostate growth habit to adapt to the mowing regime. Plant reproduction is via seed.

Knotgrass has a range of medicinal benefits and is used to treat piles, diarrhea and hemorrhages. It is also claimed to treat lung disorders, dysentery and gall & kidney stones, however most of these claims are not supported by science.

Knotgrass identification

Knotgrass Leaves

The small leaves are alternate

Knotgrass stems can grow up to a meter in length, with each stem containing may alternate, oval, green leaves. They are hairless, often seen with pointed tips and measure between 5-25mm long and 1-8mm wide. In manged turf they will be on the smaller side of the scale.

Knotgrass Flowers

The flowers self pollinating flowers are green with whitish margins

The flowering period is between May and October. The flowers are small (up to 3mm long) and are green with cream or whitish margins. They are self pollinating as they do not produce any honey or scent to attract insects.

Knotgrass Roots

The root system is shallow and fibrous, sometimes with a thin taproot

Prevention and control of knotgrass

Knotgrass can be hand weeded and physically removed, taking care to remove all of the roots. It should be noted that if seeds are present when hand weeding, they can easily fall from the pods and onto the ground when the weed is disrupted.

Raking the weed into an upright position prior to mowing well help remove stems and weaken the plant. Again this can cause the seeds to fall, if they are present.

Regular mowing will help prevent seed head production.

Avoid thin or bare areas of turf by maintaining good turf vigour with the correct turf care practices. These should include regular aeration and applying adequate nutrition.

Selective herbicides recommended for the control of knotgrass

Products recommended for professional use (The user requires the appropriate certificates to apply these selective herbicides)

  • Headland Relay Turf (Mecoprop-p, Dicamba, MCPA)
  • React Ultra (Mecoprop-p, Dicamba, MCPA)
  • Bayer Longbow (Mecoprop-p, Dicamba, MCPA)
  • Mascot Greenor (Clopyralid, Fluroxypyr, MCPA)

Products available for non-professional use (These products are available from garden centres and DIY stores.)

  • Verdone extra (Clopyralid, Fluroxypyr, MCPA)
  • Weedol lawn weed killer (Clopyralid, Fluroxypyr, MCPA)