Knotweed Control: How To Get Rid of Knotweed

Knotweed is an invasive perennial weed that commonly infests lawns. Knotweed has a habit of growing low to the ground and gradually spreads. Often it'll start out in a small area where there will be a plant or two then if it isn't dealt with can overtake a yard in a short period of time.

Knotweed is becoming increasingly common in states like Florida where about 15 species occur. Some are exotic while others are native. Knotweed spreads by creeping rhizomes and seeds. Knotweed can grow in a variety of areas such as roadsides, fields, and places that are not managed regularly. They grow in marshes and swamps, wet areas, ditches, and just about any wetland situation. A distinguishing characteristic of Knotweed is its swollen nodes where the leaves meet the stems. Leaves are spear-shaped, narrow and willow-like.

If you are having a problem with Knotweed on your lawn, our DIY Knotweed treatment guide can help. The instructions below were recommended by our lawn care experts and will show you how to properly kill Knotweed and ensure it doesn't return.

Identification

Knotweed is an annual weed that likes to grow in the early summer. This invasive plant develops slowly and by mid-summer, it is easily noticeable. The interesting thing about Knotweed is that it grows laterally rather than vertical, which is what helps it to overtake a yard and become an eyesore. Mature knotweed form mats of slender stems that are swollen at the nodes. The flowers are very small and inconspicuous. Based on its appearance, knotweed can often be mistaken for other weeds like spotted spurge or purslane but there are slight differences in the leaf arrangement and traits of the leaves.

Use the description and image above to help you to properly identify knotweed. If you're having trouble, contact us and send us a photo of your weed and we will identify it for you and suggest treatment options.

Inspection

When and Where to Inspect

Mid-summer is the best time to conduct a knotweed inspection. Look for it next to driveways and sidewalks as it can push out towards there. Knotweed thrives in any moist soil and either in full or partial sunlight. Knotweed is known to be most common in the flood plains alongside rivers and creeks. It also grows in road-side ditches, waste areas, and beaches.

As the Knotweed matures, it becomes tough, wiry and prostrate and develops a thin taproot which if you can discover early and dig out and hand pull will help to eliminate it from establishing. However by the time the weed is noticeable by midsummer it may be too late to be able to do this.

What to Look For

Look for where the knotweed is concentrated. Their leaves are long, narrow and rounded at the tip and often have a coating that looks like white powder. Knotweed flowers are small and pinkish or white.

Treatment

Before you handle any herbicides, make sure you have on the necessary personal protective equipment (PPE) such as gloves, mask, and safety glasses. If knotweed has already emerged, msm turf herbicide has shown to do a good job in controlling the invasion. In some cases where the knotweed is stubborn and persistent, a repeat application should be conducted to get better post-emergence control.

Step 1: Measure and Mix MSM Turf Herbicide

MSM Turf Herbicides covers up to 1 acre of land. Adding a surfactant to the msm turf herbicide mixture such as Nanotek Surfactant can enhance the effectiveness of the product. Apply Nanotek Surfactant per 1 finished gallon of msm turf herbicide. For knotweed control, apply 0.5 to 1 fl. oz. of msm turf per acre.

Calculate the square footage of your yard by measuring and multiplying the area length times the width (length x width = square footage) and then input the appropriate amount of msm turf herbicide in a pump sprayer or hose-end sprayer into the sprayer mixed with water. Add surfactant to the msm turf herbicide mixture at a rate of 0.24 tsp (1 gram) per gallon of the solution and agitate until well mixed.

Step 2 - Spray the Knotweed

Apply the msm turf herbicide solution to the knotweed on a fan tip nozzle spray setting to spray a fine mist that will evenly coat the weed. Spray an adequate amount all over the knotweed. Within a few days, it will start to show signs of wilting and death and before long it will be eliminated.

Step 3 - Follow Up Application

There are times when knotweed can be persistent and difficult-to-control and will need a follow-up application. Check back in 7 to 10 days to see how the Knotweed is faring and reapply after 4 to 6 weeks until the plant has totally died out.

Prevention

After the knotweed has been eliminated, you don't want it to return next growing season. For pre-emergent control, Nitrophos Barricade has shown to be effective to keep Knotweed from germinating in the spring time. Knotweed is an annual that germinates in late February or early March, so the best time to apply pre-emergent herbicide should be in the late fall. However, if it is too late and the Knotweed is out and about, you should use a post-emergent herbicide instead.

The best way to prevent knotweed from making a return and taking over is to grow healthy turf grass that will choke out any weed attempting to grow. Address compacted soil issues by reducing foot traffic on your grass. Applying mulch is another good preventative measure against prostrate weed in vegetable gardens. Coat the entire garden bed with polyethylene mulch and cut holes enough for watering around the plant.

Key Takeaways

• Knotweed is a fast-growing and extremely aggressive annual weed known to create many seeds where they are established.
• Our top recommendation for treating Knotweed is msm turf herbicide.
• A pre-emergent herbicide like nitrophos barricade can be applied to your lawn before the growing season to prevent knotweed seeds from sprouting.