Japanese knotweed

[SReynolds]

Knotweed is listed among the 100 worst invasive species in the world. It is a serious threat to waterways in Vermont and throughout the areas it has invaded in Europe and North America. Over the past 5-10 years, it has completely taken over the streambank vegetation of many rivers and streams eliminating native vegetation. Once established, it is almost impossible to eradicate. It spreads from cut fragments of stem and root/rhizome, and is suspected of spreading by seed. My own tests of seed sprouts has shown at least some seeds to be viable. It also produces a natural herbicide, a process called allelopathy. Citing a study published in PubMed, 'Allelopathy of Japanese knotweed (Fallopia japonica), giant knotweed (Fallopia sachalinensis), and Bohemian knotweed (Fallopia x bohemica) has been reported to play an essential role in its invasion. The exudate from their roots and/or rhizomes, and their plant residues inhibited the germination and growth of some other plant species.' The taxonomy (scientific naming classification) of knotweed has not settled completely, and the currently accepted name for knotweed is Polygonum cuspidatum. Streambank vegetation plays a role in the ecological functioning of the adjacent waterway; as reported in the Global Invasive Species Database, 'Invasion by P. cuspidatum can also reduce invertebrate biodiversity by half or more and reduce the quality of ecosystems for amphibians, reptiles, birds and mammals whose diets are largely composed of arthropods.' Inclusion of knotweed in this forum is justified as knotweed alters and affects the aesthetic experience and biological makeup of the waters that also support, or do not support, aquatic invertebrates.

There is an interesting situation in Addison County Vermont as of this writing. There are two main drainages coming off the western slope of the Green Mountains - the New Haven River, with its headwaters in Lincoln Vt, and the Middlebury River, a few miles to the south, with headwaters in Ripton. Of the two, the New Haven is completely taken over by knotweed from the uppermost inhabited area to its confluence with the Otter Creek, whereas the Middlebury is completely free of it. A further interesting note is that the uppermost limits of knotweed on the New Haven are in the inhabited area of South Lincoln, suggesting that the original source of this now widespread invasion was caused by garden transplants that then got loose. While the New Haven appears to be permanently altered for the foreseeable future, it is possible that with vigilance the Middlebury can remain free of it; without vigilance it seems only a matter of time.

Studies such as this one in Science Direct found a link between invasion by knotweed and reduced invertebrate diversity - quote from the abstract: 'biomass of invertebrates sampled in grassland and bush-dominated habitats was almost twice as high as that in Fallopia-invaded habitats.' We have an opportunity in Addison County to possibly investigate these findings with the examples of the two drainages above, with and without knotweed.

Eradication of knotweed is possible, but mainly only in the early infestation phase. A small patch measuring about 20 feet square was found in my neighborhood three years ago. With repeated pulling of sprouts, cutting and application of an herbicide containing glyphosate, it took two years to completely kill.

Below are pictures of the New Haven River in Lincoln Vermont, a plant in seeds in the fall in Lincoln, and a seed sprouting.

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