Knotweed, Polygonum aviculare

IPM Steps to Reduce Knotweed

1. Sample for Pest

Confirm the presence of knotweed before you treat.

Where to find it while inspecting: Compacted soils, low-oxygen soils (previously flooded). Often found next to walkways and driveways and heavily trafficked areas on sports fields such as goal mouths or between hash marks.

2. Proper ID

Is it knotweed?

Size and Appearance: New leaves are narrow and look like young grass, a compact, low-growing weed, stems grow thick and tough with age and bear many leaves.

3. Learn the Pest Biology

What is the life cycle of knotweed?

Life Cycle: Seeds germinate in early spring with a bright green flush of new growth, then grows slowly and can grow into mats 3–4 ft wide. Seeds develop low to ground and seedlings survive mowing. Flowers may appear all summer and into fall, and seeds are long-lived in the soil.

Preferred Habitat: Compacted soils, usually where turfgrass has struggled to survive.

4. Determine Threshold

How much knotweed is too much?

Threshold: Act when you find knotweed in prime turf areas or gardens, as it can be harder to control once well-established.

5. Choose Tactics

Best management practices to reduce knotweed:

Best Management Practices: Reducing compaction is the best way to slow knotweed infestation. So aeration of prime turf fields is essential. Watch for new plants in early spring and remove. Frequent low mowing in spring may slow spread. Encourage new turfgrass growth by keeping soil aerated and maintaining proper soil pH: 6.0 to 6.8 (test every 3–5 years). Fertilize at the proper time for turfgrass root development, primarily fall (late spring at times when turf is weak and thin), irrigate if needed, mow at proper height (removing no more than 1/2 of the blade), amend poor soil, choose proper turfgrass seed for your conditions, buy quality seed, overseed thin spots in fall or early spring, remove thatch.

Treatment Methods: Treatments include manual removal of young plants, aerating soil and overseeding with proper turfgrass seed, and when heavily infested, pre or post emergent broadleaf herbicide where allowed.

6. Evaluate

Was the tactic successful? Record the date pests were first noted, and the tactic you used, and its success. Use one of our RECORD KEEPING tools.

For More Information:

Penn State Extension: Prostrate Knotweed

Penn State Extension: Weed of the Month: Prostrate Knotweed

Remember:

When a pesticide application is necessary, all necessary and required precautions are taken to minimize risk to people and the environment and to minimize risk of pesticide resistance or pest resurgence. Pesticide use in your school may be prohibited or regulated by local policies or state and federal regulations. Risk reduction methods can include, but are not limited to, spot-treatment, the use of gel or paste bait formulations placed in inaccessible locations, injection into a crack or crevice, and other methods that reduce potential exposure.