Japanese & Giant Knotweed
Polygonum cuspidatum & Polygonum sachalinese
Why is it a problem?
Introduced from Asia in the early 1800s, knotweed is an invasive species in Michigan that is illegal to sell or plant due to the significant threat it poses. This aggressive species forms dense monocultures that disrupt soil nutrient levels and exhibits allelopathy. Knotweed is exceptionally resilient, capable of growing through asphalt and concrete, making it a challenge for management and eradication.
How to identify?
Knotweed can reach heights of 3 to 10 feet and spread laterally up to 65 feet through an extensive root system. Its broad, alternate leaves have pointed tips and the plant produces distinctive white, spiky flowers. The stem of knotweed is hollow and whitish, resembling bamboo, which is where the name people refer to as "Michigan bamboo" comes from.
How to manage?
Mechanically pulling knotweed is generally ineffective and can often aggravate knotweed and causes the population to spread further. When stressed, knotweed tends to send out additional roots, worsening the infestation. For effective treatment options, check out the DNR's recommendations (link).
