Japanese Knotweed - Amy Stone


Often we take notice of invasive plants when they are most obvious when they are in bloom, have put on their yearly growth and are standing tall or maybe wide in some cases, and really can't be missed. But today, I wanted to share an early view of an invasive perennial, Japanese knotweed (Fallopiajaponica). That review includes last year's left-overs, hollow stems standling leafless. No new growth will be initiated from these above stems and soon will be masked or hidden by this year's new growth. 

Japanese Knotweed Stems for 2019Photo Credit: Amy Stone

Below is this year's new growth. Noticed the arrow shaped leaves. 

Japanese Knotweed Emerging from the Ground in Spring Photo Credit, Amy Stone

The photo below was taken last year as the plant growth is progressing. Note the hollow stem from a stalk from last year, and stem color from this year's growth. 

Japanese Knotweed with Leaf Fully Emerged and Hollow StemPhoto Credit: Amy Stone

Plant Characteristics: 

  • Perennial, herbaceous type-shrub that can grow from 3-10 feet high each year
  • Stalks are hollow and persistent through winter, looks similar to bamboo
  • Stems have a fine white coating that rubs off easily
  • Stems have purplish specks or small spots
  • Flowers arranged in spikes near the end of the stem are small, numerous, and creamy white in color
  • Flowers bloom later in the summer in Ohio
  • Prolific seed producer

The Ohio Invasive Plant Council (OIPC) has an Fact Sheet that could be a useful tool if people are trying to manage this invasive plant. https://www.oipc.info/uploads/5/8/6/5/58652481/10factsheetjapaneseknotweed.pdf

We are encouraging folks to report locations of where this plant is growing using the Great Lakes Early Detection Network (GLEDN) app. If you have not used the app before, it is an easy app that includes invasive plants, insects, diseases, and wildlife. The app uses the EDD maps were locations of the reported species are indicated once verified. For additional information about the GLEDN app, check out the website or search your app store on either your iPhone or android phone at https://apps.bugwood.org/apps/gledn/

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