Botanical name: Polygonum aviculare
Aliases: Common knotgrass, knotweed, matgrass, doorweed, birdweed, pigweed, wireweed
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 – 60 cm, 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, diarrhoea and haemorrhages. It is also claimed to treat lung disorders, dysentery and gall & kidney stones, however most of these claims are not supported by science.
- Leaves: 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 5-25 mm long and 1-8 mm wide. In manged turf they will be on the smaller side of the scale.
- Flowers: The flowering period is between May and October. The flowers are small (up to 3 mm 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.
- Roots: Knot grass has a tough, wiry taproot (see image below).
Knotgrass Images (click image to enlarge)
Prevention and control
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)