photo courtesy of KISMA/Sigrid Resh KISMA technician holds up invasive knotweed.

Why should you care about knotweed?

Knotweed is a large, aggressive plant that forms dense stands and can damage infrastructure (e.g., fences, septic fields, and cement) and ecosystems. Also, knotweed is able to spread easily within a site through its large network of roots.

Knotweed is most often spread from site to site by plant fragments, meaning people, vehicles, or water moving plant fragments. This movement of fragments allows the knotweed to establish new infestations.

Japanese knotweed and its hybrids/cultivars are illegal to sell, trade, move, plant, or share in Michigan, per Michigan’s Natural Resources Environmental Protection Act (Part 413 of Act 451).

The Keweenaw Invasive Species Management Area (KISMA) is collaborating with the Alger County Conservation District to survey for and manage invasive giant and Japanese knotweed (Fallopia spp.) in the Central and Western Upper Peninsula.

This project is funded through the Michigan Invasive Species Grant Program for 2021-2023.

KISMA’s goals with this grant are:

• Prevent the spread of invasive knotweed throughout Houghton, Baraga, and Keweenaw Counties via outreach and education

• Treat priority sites with invasive knotweed to eradicate current populations

• Conduct outreach workshops to educate landowners and the public about the threats of invasive knotweed

• We have found 115 patches of knotweed in the tri-country area, with more being discovered or reported each week. We are helping to treat approximately 40 infestations.

Management of knotweed consists of 5+ years of manual removal of aboveground plant material every 2-3 weeks through the growing season (dry fully on pavement, tarp or bag and take landfill) or repeated treatments with herbicide.

Please contact KISMA (kisma.up@gmail.com) for help establishing a management plan if you have invasive knotweed on your property.

Patches of knotweed that are in close proximity (65 feet) to each other are likely connected below ground and need to be managed together for successful control. This is creating neighbor conflict in our area!

Because knotweed spreads primarily through fragmentation, proper disposal is a very important final step in management! There are several ways in which the plant parts can be disposed of, including burning, bagging, and taking to a landfill, or by fully drying in the sun while avoiding contact with the soil.

The most important first step for public awareness is the proper identification of knotweed:

• Starts as small shoots in early- to mid-May; by early summer reaches heights of 10+ feet

• Stems are upright and segmented – similar to bamboo, but not woody

• Leaves are large, growing 10+ inches in length. Japanese knotweed has round leaves with a flat base and a pointed tip, while Giant knotweed has larger, heart-shaped leaves

• Flowers late in the summer, with white spikes with small petals. They very rarely seed but have small, winged seeds when they do

• A large and robust rhizomatous root system that can grow 6 feet deep and 65+ feet long.

• Stems become hard and brown and often remain standing through the winter months

• Shade intolerant

Frequently mistaken native look-alikes include: Red osier dogwood (Cornus sericea) and young Basswood (Tilia americana) shoots. Knotweed is frequently found in heavily disturbed sites and urban areas. Once established, it takes years of frequent management to restore a site. Consequently, identifying it before it becomes well-established is crucial. Reforestation is one of the best long-term, sustainable control measures for this invasive species.

Additional Resources:

• KISMA website: https://www.mtu.edu/kisma/

• Michigan Invasive Species Information Network (MISIN): https://www.misin.msu.edu/