Beware! Japanese Knotweed
***Save our Stream Ways***
Japanese knotweed is coming up now in ditches and waterways all over our community
Have you noticed Japanese knotweed (Reynoutria japonica) in our neighborhood or along Old Dominion Road? The nickname for Japanese knotweed is “Godzilla weed” because it spreads rapidly, is difficult to eradicate, and causes massive damage to our native habitat. Dense stands of Japanese knotweed have no known value for our native wildlife, and are rapidly taking over our local stream banks, wetlands, drainage ditches, and forest edges.
One reason for the highly successful invasion of Godzilla weed is that just fragments of the stem and rhizome (a thickened, horizontal root) can break off and start a new plant. This occurs easily during rain events that result in large volumes of storm water and runoff that cause erosion. Such events are becoming more and more frequent due to climate change and an increase in impermeable surfaces.
Seemingly innocent, early Japanese knotweed shoots resemble red asparagus
Japanese knotweed was introduced to this country in the 1880s to stabilize stream beds. Once established, it continues to spread very quickly and can grow over seven inches per day, competing with and displacing native plants such as tree seedlings. This can have an impact on birds and fish because they rely on the food sources that rely on trees!
On this iNaturalist map, you can see just some of the locations where Japanese knotweed has been spotted in our Franklin Park & Forest community.
Japanese knotweed has a distinctive, shield-shaped leaf with a flat base and pointed tip
Japanese knotweed can be cut back, but cutting alone is not going to be an effective control. It is nearly impossible to dig out, as the rhizomes can be up to nine feet deep and spread over 20’ in all directions.
Other measures must be taken, such as covering the area with hardware cloth to girdle new shoots, tarping the area to prevent photosynthesis, or spraying with an appropriate herbicide. All cut stems, leaves, and any unearthed rhizomes need to be bagged and disposed of in the trash. Do NOT compost any part of Japanese knotweed and do NOT put it into your yard waste bins!
Wide swaths of Japanese knotweed are taking over the Pimmit Run stream valley
Japanese knotweed is classified as a HIGH invasive risk on the Virginia Invasive Species Plant List from the Virginia Department of Conservation and Recreation. In fact, it is considered one of the most highly invasive plants worldwide. It is so destructive, in Britain major mortgage lenders will not finance a house if Japanese knotweed is found on the property!
If you see Japanese knotweed on your property, take action immediately! Please don’t let Godzilla destroy our community.
More information:
Penn State Extension Fact Sheet on Japanese knotweed
How to Remove Japanese Knotweed
Fairfax County Park Authority Citizen's Guide to Non-Native Invasive ID and Control
Virginia Department of Conservation and Recreation Invasive Plants Information