1. What is Japanese knotweed?
2. What research has been done on Japanese knotweed in Greene County?
3. How does Japanese knotweed spread?
4. How do I identify Japanese knotweed?
5. What can I do about Japanese knotweed on my property?
6. Once I have removed Japanese knotweed from my property, how should I revegetate the area?
Japanese knotweed (Fallopia japonica), originally from Asia, is a non-native invasive species that has established stands along several roads and streams in Greene County. Once established, this perennial shrub spreads quickly. There is concern that Japanese knotweed has negative impacts on streambank stability, thereby contributing to increased turbidity and decreased water quality within several streams in Greene County and the New York City watershed. Japanese knotweed forms dense thickets that have been known to threaten native plants, damage infrastructure, reduce visibility, and block passage routes used by animals.
The Greene County Soil & Water Conservation District has worked collaboratively with the New York City Department of Environmental Protection (NYCDEP) and Hudsonia Ltd. to study Japanese knotweed within the Batavia Kill watershed. Hudsonia Ltd. first conducted a literature search and review to gather information regarding the biology, ecology, and management of Japanese knotweed. The next step in our research efforts was to determine the extent of knotweed cover along the Batavia Kill streambanks and floodplain. Using ArcGIS 8.3, Hudsonia Ltd. conducted a remote vegetation analysis within the riparian corridor of the Batavia Kill, mapping vegetation types and knotweed occurrences. Japanese knotweed is prevalent along the Batavia Kill.
Additionally, research has been conducted on the soils, vegetation, and biota associated with knotweed stands along the Batavia Kill. The findings of the remote and field studies of knotweed can be found in Hudsonia Ltd.'s draft report, Japanese Knotweed Maping and Sampling on the Batavia Kill, Greene County, New York.
Monitoring Japanese Knotweed Stands at Restoration Sites in the Schoharie Basin
Controlling Japanese Knotweed Stands at Stream Restoration Sites
Japanese knotweed spreads by cut fragments of the plant's stem or root system (rhizome). Often found along rivers and streams, Japanese knotweed can be spread by cuttings that travel in waterbodies. Japanese knotweed stands found along waterbodies are especially difficult to control, as upstream sources will need to be managed as well. Root fragments of knotweed plants are known to spread through the movement of soil, especially during excavation, construction, or road building.
Knotweed can spread by even the smallest live clippings (1/2 an inch) of stem or rhizome. Mowing and chipping live plants should be avoided, as those techniques can spread live stem fragments. Tilling and excavating soil around Japanese knotweed should also be avoided, as those techniques can spread live rhizome fragments. When handling Japanese knotweed cuttings, take care to ensure they do not get blown away, have contact with soil, or wash into nearby streams.
Knotweed starts growing in late-March to mid-April. Below are photos of Japanese knotweed by season:
Thick, reddish stalks sprout up early, resembling asparagus stalks. These tender stalks are edible at this stage!
Late Spring and Early Summer
Hollow stems grow quickly, oval leaves pointed at the tip unfurl in zigzag pattern, plant spreads by deep, extensive rhizomous root system.
Late Summer and Autumn
Flowering usually occurs in July. Sprays of white or reddish-pink flowers attract bees and other insects.
Late Autumn and Winter
The dead, reddish-orange stalks remain for up to two years. These hollow stalks resemble bamboo.
First, it is important to understand that managing Japanese knotweed can be very difficult. Most management strategies take several years before they are successful, and sometimes complete eradication of Japanese knotweed is not possible.
The best method for controlling Japanese knotweed is to prevent the establishment of knotweed or to catch it right away when the plants are small (knotweed stems begin to emerge in late-March to mid-April). If knotweed is established, eradication can be achieved by removal, disposal, and revegetation. There are four types of removal methods: manual (pulling or digging), mechanical (cutting), chemical (herbicides), or a combination of several methods. A combination of methods is the most effective, so it is a good idea to select several approaches. It is important to know that most control methods take years of dedication in order to be successful.
After removing knotweed, it is best to encourage the growth and establishment of native plants. In some situations native plants will readily re-establish themselves without any help. To jumpstart the process of revegetation, consider planting large, fast-growing native trees and shrubs that will eventually shade out previous knotweed patches. If revegetating streambanks, planting woody plants along the edges of streams is also beneficial for stabilizing the streambanks to help prevent erosion. Once Japanese knotweed has been removed from your property, it is essential to keep monitoring the site to make sure that re-infestation does not occur. Evaluate your site in May-June to gauge the effectiveness of your control methods. When revegetating, it’s best to follow a 10-day wait period from the time of the last herbicide application.
The Catskill Streams Buffer Initiative (CSBI) provides funding and assistance for invasive species control and revegetation. Riparian (streamside) landowners in the Schoharie watershed may be eligible. For technical assistance, more information, or to see if you qualify for a CSBI project in the Schoharie watershed, contact the Greene County Soil & Water Conservation District at 518-622-3620.
For information about controlling Japanese knotweed:
For general information about Japanese knotweed: