Plan the perfect garden with our interactive tool →

How to Kill Prostrate Knotweed in Lawns

Knotweed is sometimes also called prostrate knotweed because it creeps along the ground rarely achieving more than 4 inches in height. The long tendrils creep out in a spider-like pattern and have tiny leaflets that resemble knots along the stems. The plant is an annual, but each plant disperses an abundance of seeds that germinate the following spring. Killing prostrate knotweed requires the use of both post-emergent and pre-emergent herbicide solutions.

Step 1

Fill a pump-style garden sprayer with an herbicide that contains two of the following ingredients dicamba, 2,4-D, triclopyr, MCPP and clopyralid. Do not mix multiple products. Instead, find an herbicide that already contains multiple active ingredients.

Step 2

Add water to the sprayer and then close it up by screwing on the top. Shake the sprayer gently to mix the solution and then pump the handle of sprayer up and down until you feel resistance.

Step 3

Spray the mixture onto all areas of the prostrate knotweed, making sure to saturate the plants. If the knotweed plants are still young, less than 3 inches in diameter, one application of herbicide will kill them. For larger knotweed plants, wait one week and apply a second dose of herbicide to the plants if any green coloring is detected.

  • Fill a pump-style garden sprayer with an herbicide that contains two of the following ingredients dicamba, 2,4-D, triclopyr, MCPP and clopyralid.
  • For larger knotweed plants, wait one week and apply a second dose of herbicide to the plants if any green coloring is detected.

Step 4

Wait until the following February before the grass and weeds start producing green growth. Apply a pre-emergent herbicide to the entire lawn that contains one of the following ingredients, benefin, isoxaben, oryzalin, dithiopyr, prodiamine, pendimethalin or trifluralin. Use the amount specified on the herbicide bottle. This prevents any remaining prostrate knotweed seeds from germinating.

Related Articles

How to Kill Grass Burrs
How to Kill Grass Burrs
Directions for Eliminator Weed & Grass Killer
Directions for Eliminator Weed & Grass Killer
How to Kill Kikuyu Grass Weeds
How to Kill Kikuyu Grass Weeds
How to Test the Quality of Roundup
How to Test the Quality of Roundup
Examples of Herbicides
Examples of Herbicides
How to Mix Up Killzall Herbicide Concentrate
How to Mix Up Killzall Herbicide Concentrate
How to Use Glyphosate
How to Use Glyphosate
How to Plant Rapeseed
How to Plant Rapeseed
How to Use Salt to Kill Grass
How to Use Salt to Kill Grass
How to Kill Wild Violets in Lawns
How to Kill Wild Violets in Lawns
The Best Way to Kill Weeds in Centipede Grass
The Best Way to Kill Weeds in Centipede Grass
Homemade Thistle Killer
Homemade Thistle Killer
Ingredients in Trimec Plus Herbicide
Ingredients in Trimec Plus Herbicide
How Can I Kill Sagebrush?
How Can I Kill Sagebrush?
Garden Guides
×