Japanese Knotweed in Laurel Park
Japanese knotweed (Reynoutria japonica) is a fast-growing, opportunistic invasive plant that has taken hold in many parts of North Carolina—including Laurel Park. With its bamboo-like stems, heart-shaped leaves, and ability to form dense thickets, this non-native perennial is more than just an eyesore: it’s an aggressive invader that outcompetes native plants, degrades ecosystems, and is exceptionally difficult to eradicate.
Japanese Knotweed along the stream in Laurel Green Park
A Severe Invasive Threat
The North Carolina Invasive Plant Council classifies Japanese knotweed as a “Severe Threat”, meaning it is known to displace native species, alter ecosystem functions, and resist most forms of control. In addition to being a strong competitor, Japanese knotweed also has allelopathic properties—chemicals released by the plant can inhibit the growth of surrounding vegetation
Why Knotweed Is So Hard to Manage
What makes Japanese knotweed particularly challenging is its complex underground rhizome system, which can regenerate new shoots from even tiny root fragments. Research has shown that very small fragments can produce new growth. This robust underground network makes physical removal difficult and often counterproductive.
Cultural control methods—such as cutting, mowing, or digging—are typically ineffective and can worsen the problem. Repeated cutting may reduce visible growth but does little to weaken the root system. Digging often leaves behind small root pieces that quickly resprout.
The Physiological Basis for Herbicide Control
Herbicides remain the most effective control option, especially when used in accordance with the plant’s seasonal biology. In late summer and early fall, knotweed moves carbohydrates (and systemic herbicides) into its rhizomes for winter storage. This makes late-season herbicide applications particularly effective.
Systemic herbicides, such as triclopyr, exploit this process by traveling through the plant’s vascular system and reaching the underground storage organs.
⚠️ Important: Only use aquatic-approved formulations of triclopyr near waterways, wetlands, or riparian zones.
Three Key Steps for Managing Japanese Knotweed in Laurel Park
1. Late-Season Herbicide Application (August–September):
Apply triclopyr to actively growing foliage after flowering but before the first frost. This takes advantage of the plant's natural downward nutrient transport. A second application about two weeks later is often most effective.
2. Follow-Up Treatments in Subsequent Years:
Complete eradication typically requires multiple years of treatment. Monitor the site each season and retreat any regrowth. Avoid mowing or cutting between applications, as this reduces herbicide uptake.
3. Prevent Disturbance and Restore with Native Plants:
Once the infestation is under control, stabilize the site with native vegetation or other erosion-control methods. Carefully dispose of plant material to prevent spread and avoid soil disturbance that may trigger regrowth from residual roots.
Be Aware and Report New Infestations
Laurel Park residents can play a vital role in controlling knotweed by learning to recognize it and preventing its unintentional spread. Effective management requires long-term commitment, accurate identification, and community-wide coordination.