Japanese Knotweed Along Madison’s SW Bike Path: Update on Control Efforts

Japanese knotweed (white flower) growing in the storm water ditch below the SW Bike Path.

Japanese knotweed (white flower) growing in the storm water ditch below the SW Bike Path.

Madison, WI September 10, 2014.  This blog has written about Japanese knotweed in Madison before.  In an earlier post we reported on the extensive forest and scattered outliers of Japanese knotweed (Polygonun cuspidatum) that infests portions of the SW Bike Path and adjacent storm water drainage channels between Glenway St. and the Sheldon St./Fox Ave./Virginia Terrace intersection   The epicenter of the knotweed infestation is along the northern path shoulder and in the storm water ditches roughly between Glenway Golf Course and the Forest Hill Cemetery.

I don’t believe the extent of the infestation has been officially mapped using GPS technology so my estimate of the total area of the patch—not counting outliers—is approximately 3-4 acres. The height of stems ranges from 3’ to 10’ and stem density is so tight and the shade from the leaf canopy so thick that very little else grows in this thicket.

Here the native Brown-eyed Susan (Rudbeckia) is able to find space on the edge of the knotweed clone.

Here the native Brown-eyed Susan (Rudbeckia) is able to find space on the edge of the knotweed clone.

The Japanese knotweed invasion front is steadily moving in all directions as human activity and storm water flow move seeds and root fragments around. Knotweed is moving east and west along the northern path shoulder; it is creeping north up the storm water channels towards the Glenway Golf Course, Glenway Woods, and the Forest Hill Cemetery; and, the weed has crept under the SW Bike Path and is encroaching upon neighborhood backyards that adjoin the southern edge of the bike path.

The Larger Threat

The concern about Japanese knotweed extends beyond the narrow confines the SW Bike Path and extends to the wider downstream Wingra Watershed including the wetlands surrounding the lake and Lake Wingra itself.  If Japanese knotweed is not contained or eradicated on the bike path, all these downstream areas are at risk of being invaded by Japanese knotweed.

Japanese Knotweed—A Fearsome Plant

As we reported back in 2012 (click here for the post)

“In the world of weeds, there are few that are the equal of Japanese knotweed (Polygonum cuspidatum). By any measure: aggressiveness, economic impact, and near impossibility of control, Japanese knotweed is a fearsome invasive plant.”

“The excellent book “Invasive Plants of the Upper Midwest” (Czarapata, 2005, p 73-75) describes Japanese knotweed thus:”

“Japanese knotweed spreads rapidly by rhizomes forming large, dense thickets that eliminate native vegetation and wildlife habitat. The rhizomes are strong enough to penetrate pavement. Knotweed thickets are particularly problematic along waterways . . . It is also one of the most troublesome weeds along railroad rights-of-way because it becomes a fire hazard during the dormant season. Once established, Japanese knotweed stands are extremely difficult to eradicate.”  “Established” means it’s been growing in one area for years and is expanding the patch size by moving into new areas.”

This is the exact situation (waterways, railroad-now-bike-path-corridor, established thicket, expanding population, and hazard of potential fire) the City is faced with in September, 2014 along the SW Bike Path.

Japanese knotweed flowers

Japanese knotweed flowers.

What Could Be Done?

In every situation of pest plant invasion there are four options:

  1. Ignore the problem.
  2. Contain the weed (eliminate the outliers and stop the spread).
  3. Control the weed (shrink the size of the clone.)
  4. Eradicate the weed ( kill the entire clone and all isolated populations and plants.)

In this case Option 1 is not responsible or practical. Each of the other three options will need a long-term commitment of funding and resources and a strategic, systematic, and thorough approach, supported by continual monitoring and follow-up actions.

Achieving even containment will need several years of sustained effort; control and eradication will take longer.

In an earlier post we recommended a containment strategy focused on starting with a small-scale pilot project to contain the patch by stopping the spread at the edge of the invasion front, and then over time gradually shrinking the patch size.


The apparent, and possibly unrealistic,  goal of the City and contractor is eradication of Japanese knotweed.  The apparent management strategy was a mass assault, a clear-cut to crush the plant into submission.”

“An alternative, achievable goal in this situation would be to contain the population within current boundaries and prevent the spread of the plant to new areas by first attacking the outlying patches of Japanese knotweed, say the ones at either end of the bike path and those that have sprung up in back yards.     When the expansion is halted and the population stabilized, the managers can continue to tighten the noose.  This small-scale approach could achieve the desired outcome of preventing the problem from becoming worse, but would need lots of handwork, persistence, and on site supervision.  Volunteers could be recruited to tackle  small patches in their section of the bike path.  This volunteer efforts would help the City supplement its limited resources.”

 “This small-scale approach would also let the City  build upon a record of successful pest plant management and, would have the added benefits of education, outreach, and public engagement.”

What Has and Is Being Done?

To its credit—and at the urging of neighborhood Path leaders and volunteers—the City of Madison Engineering Division hired a contractor in 2013 to apply herbicide to knotweed along the South West Bike Path.

Japanese knotweed stem after herbicide application.

Japanese knotweed stem after herbicide application in 2014.

During 2013 it was not apparent what the goal was or what strategy and tactics were used. Patches and isolated plants were cut and an unknown herbicide was applied to the cut stem surface.   The work seemed to be sporadic and random although in places the Japanese knotweed stems were top-killed. It is not yet known if the knotweed roots were killed too, because there was some re-sprouting from the root stocks.

Keeping At It

In 2014 City Engineering—without notifying DMNA and other neighborhood path leaders—hired a different contractor to apply herbicide to wild parsnip, knotweed, burdock, and a few other weed species.   This effort got off to an unfortunate start as untrained workers from the contractor mistakenly killed the native Golden Alexander plants in the DMNA prairie at Odana Road and the bike path, when they mistook the Golden Alexander (Zizia) plants for the much different wild parsnip (Pastinaca sativa).   It is telling that the contractor’s workers apparently could not identify native prairie plants and seemingly did not even realize they were in a planted prairie.

As a result of this fiasco, the City has asked the contractor to work closely with neighborhood path leaders to identify native planting areas that are off limits to herbiciding and to establish weed control priorities for the contractor.

 Back On Track

Sandy Stark, chair of the Dudgeon-Monroe Neighborhood Association (DMNA) bike path committee describes the neighborhood approved activities in an article in the current issue of the DMNA Hornblower:

“The flip side to spring rains is the density of weeds and invasive plants along the path corridor. You may have noticed selected mowing and targeted herbiciding of areas by a city-contracted company. This fall, watch for roped-off areas of knotweed due for special treatment, and roped off to keep them from being mown or cut, since that just encourages increased growth of the plant itself. (While mowing may slow down growth, it counteracts real progress in containing the spread if not combined with other treatments.)”

 “In the short-term, you will see mowed plants, cut shrubs, and piles of browning debris. These will be cleared later by the contractor or city crews. In the long-term, you should see a healthier, more attractive corridor emerge. A coalition of experienced neighborhood green space groups from the Beltline to campus has re-organized and partnered with City Engineering to work toward a maintenance plan that accomplishes just that.”




About Steve Glass

The blogger is a restoration ecologist, Certified Ecological Restoration Practitioner (#0093 SER) and writer living in the Midwestern United States.
This entry was posted in Invasive species, Neighborhood restoration projects, Pest species, SW Bike Path. Bookmark the permalink.

One Response to Japanese Knotweed Along Madison’s SW Bike Path: Update on Control Efforts

  1. Pingback: Process to Eradicate Japanese Knotweed Along SW Bike Path Continues | WingraSprings

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