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April 24, 2006



That's really interesting stuff, especially the transpiration of glyphosate, which makes perfect sense. I don't know the details of the knotweed control issue--thanks for giving me a better context to understanding their decision. Do you know if they have looked into mycellium based herbicides? There is a product being studied here in Vermont for ROW's that might be applicable if it continues to be produced. It's also painted on, usually to cut stumps, as a glyphosate substitute. The company previously producing it has since filed for bankruptcy.

PS. By the way, Green Mountain College is offering a new program--MS in Environmental Studies. The program sounds great. If you know anyone interested, you might pass this link along. It's a limited residency program designed for professionals.


Tim Abbott

Lene, from a purely biological perspective, Japanese knotweed (Polygonum cuspidatum) is very difficult to control. It is rhizominous and can reproduce vegetatively. It is virtually impossible to pull up every fragment of the plant by hand or mechanically. I have tried smothering it in dense layers of black plastic, and found living knotweed persists even two years later. It is particularly aggressive in riparian areas, banks and river corridors, and mats of uprooted knotweed can float downstream in floods and reestablish with ease.

It has a hollow stem like Phragmites, and therefore TNC has applied what it has learned about controlling that plant species with cut stem application of Rodeo to controlling knotweed. My old TNC program, the Berkshire Taconic Landscape Program, pioneered this method at Kampoosa Bog in Stockbridge MA where there is a highly sensitive habitat and many rare species. Because the Phragmites stem draws the herbicide down to the Rhizome, the clip and drip method is the least objectionable from a non-target impact perspective.

There are some drawbacks to hollow stem application. Herbicide can sit in a well above the node for a while before being drawn down by the vascular system of the plant and if it rains a few hours after treatment, the herbicide can leak out of the cut stem. One very hot days with high humidity, Phragmites Rhizomes appear to release Glyphosate after treatment. TNC has documented cattail die-back within a foot or so of the stem on such occassions and other researchers confirm this observation.

Knotweed has a much wider stem than Phragmites, and TNC's own Element Stewardship Abstract for this species says the following about Glyphostate and herbicide application protocols:

"A number of biocidal chemicals have been found to be effective against Polygonum cuspidatum. Most of these are undesirable for use in conservation areas because they are nonselective, may be persistent in the soil and/or are not safe for use near water. One frequently used way to minimize the effects of non-selective herbicides on non-target species is to paint herbicides directly onto the target plants (Broaddus, pers. comm.). In the case of P. cuspidatum, this would probably require prior cutting for easier access if herbicides are to be applied after the plants have reached their full height. Herbicides appear to be more effective when combined with cutting (Scott and Mars, 1984; Orchowski, 1991).

Glyphosate [N-(phophonomethyl)glycine] has been found to be very effective against Polygonum cuspidatum (Ahrens, 1975; Beerling, 1990; Pauly, 1986). Glyphosate is a nonselective systemic herbicide with a short residual life (Ahrens, 1975; Lynn, Rogers and Graham,1979). Application is more effective in the fall when leaves are translocating to rhizomes (Lynn, et al, 1979). The British Nature Conservancy Council (1989) recommends applying 2.0 kg/ha in August with a prior cut in late spring or early summer. Glyphosate is available from Monsanto under the trade names RoundupTM and RodeoTM. Only Rodeo has been approved for use near water (Bender, 1988). Glyphosate has been used with limited success on some nature reserves in the U.K. (Palmer, 1990). Repeated applications over several years may be necessary (Beerling, 1990; Palmer, 1990; Pauly, 1986)."

Cut stem application requires a higher concentration of Glyphostate than foliar spray. TNC uses a 25% solution of Glyphostate for its Phragmites control at Kampoosa. It is labor intensive, and often volunteers precede a licensed herbicide apoplicator to cut the stem and remove the upper portion of the plant for composting offsite.

My question to TNC is what specifically are the unacceptible impacts on biodiversity of the knotweed at the sites where it has decided to control this species. I would hope TNC would not choose to manage this plant simple because it is invasive, but rather because it directly threatened the viability of a particularly rare or irreplaceable species or an outstanding example of a more common natural community type.

I have seen it at its worst on the scoured gravel banks and low islands of major rivers where it dominates these naturally disturbed habitats, and along embankments. Presumeably there are some natural communities and rare species which might be threatened by Knotweed at certain sites, but it is not, at least as far as I am aware, capable of overwhelming vast areas the way that Phragmites and Loosestrife can.


Thank you for taking time to explicate the theory concerning herbicide use and invasives. Japanese knotweed is a major plant of concern up here, and I've heard that TNC is using stem injections rather than broadcast spraying even though it requires several times more active ingredient per sector of land and has proven to be less effective at controlling the plant. Do you know why they might be choosing to use stem injection versus spraying?

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