Eradicate a foliar felon

#MiddleburyCT #MiddleburyLandTrust #Knotweed

Knotweed surmounts a fence, showing off lovely blooms that appear in late summer. This very invasive plant spreads by seed as well as an impressive rhizome system and is extremely difficult to eradicate. (Alyssa Siegel-Miles, UConn Extension, photo)

By JANINE SULLIVAN–WILEY

You may have seen them proliferating along roadsides, streams and rivers, the foliar felons called by an innocent-sounding name: knotweed (also known as Japanese knotweed). Reynoutria japonica has the dubious distinction of being one of the most invasive species in the world. It has become a scourge in Europe, where England spent about $70 million euros to remove it from the area needed for their 2012 Olympics, and it is now in 42 of the 50 U.S. states.

What makes this plant such a thug of the plant world? As is often the case with a nonnative plant, nothing outside of its native home in Japan eats it. It is also staggeringly robust and resilient. One almost – but not quite – has to admire its unique attributes. Knotweed can survive temperatures of -31 degrees Fahrenheit. It can grow five feet in a month. Its roots (rhizomes actually) can spread 20 feet horizontally and grow down 10 feet.

It aggressively outcompetes any native plants. It likes disturbed areas along roadways and trails and riparian areas along streams and rivers. Its only real requirement is that it needs sun.

How did we end up with this indomitable plant? As with most of our problem invasives, gardeners in the 1800s brought it here intentionally for its flowers, and communities used it to control erosion, thanks to its fast growing and robust properties. (This is a cautionary to all gardeners: If it says, “grows rapidly,” “not bothered by pests” – don’t go near it!)

The English recognize it as such a villain that people there may be unable to get a mortgage on a property with knotweed. Here, individuals, organizations and states are battling a foe that can seem invincible.

Does it have any redeeming qualities? The shoots are apparently edible when very young and cooked, tasting like rhubarb. (I’ve never tried it so don’t ask for recipes.) Beekeepers love it, as it is a heavy, late-season bloomer. They make what is called “knotweed honey” from it. Traditional Asian medicine has used knotweed for centuries, but scientific evidence for those uses is limited.

Various methods of eradication help us do battle against this foe. One can successfully pull out a new, small bunch, but once it has become established, it gets very hard to kill. Burning doesn’t work because the roots are too deep; it grows back. Digging it out makes any remaining bits of rhizomes kick into high gear and spread farther. Weed-whacking or mowing spreads tiny bits that can become new sprouts.

While researchers are exploring a few experimental removal efforts, the removal method known to work is labor intensive: Cut it off near the ground, forcing the rhizomes to use their resources to grow back. With the ground exposed, plant natives on the now-sunny ground, and they will do their part to shade the re-growing knotweed. Cut any new shoots back three times a year; it may take three years before no new sprouts appear. Importantly, each time the tops are cut off (or young plants pulled), the cuttings should be burned or dried out to kill off the stems. Even a small piece can start a new plant.

The last method, but one that should be avoided if the infestation is small, is the use of herbicides such as Round-Up. While herbicides are effective against knotweed, they are potentially dangerous to people, especially the person applying them. Extreme care should be used if going this route.

This summer, the Middlebury Land Trust is embarking on a major effort to remove knotweed from its properties. If you are interested in having some fun out in the fresh air cutting down this nasty invasive, your help would be hugely appreciated. The plan is to do this in manageable doses, so don’t be intimidated. Contact Alice at akhallaran@gmail.com as she is organizing teams and dates.

Contact this writer at jswspotlight@gmail.com. You can visit the Middlebury Land Trust on Facebook or the website at middleburylandtrust.org. Happy hiking!