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Knotweed is sprouting and spreading

Jamie Myers of the National Park Service holds an enlarged photo of an Aphalara itadori, a tiny species of jumping plant louse, which British researchers have found effective in controlling Japanese knotweed. U.S. researchers petitioned for release of the lice for knotweed control following tests of the lice’s control capabilities done at the University of Washington completed in 2011. Their petition is still under review by the U.S. Department of Agriculture.
TRR photo by David Hulse

By David Hulse
May 7, 2014

NARROWSBURG, NY — If you’ve been along the river’s shore lately, there is a good chance you’ve seen bright red sprouts pushing through the shoreline soil.

It’s a good chance because an invasive weed, Japanese knotweed (Fallopia japonica) has spread widely along the valley and no generally accepted means of controlling its spread exists—at least in this country.

For those who haven’t noticed, knotweed imitates bamboo in some respects, grows in dense clusters along the shoreline and becomes apparent in late summer when it produces attractive white blossoms in large quantities.

Knotweed is a problem, in part, because its dense growth overwhelms native plants, and while its deep rhizome roots spread readily, they do not hold the shoreline together against annual high-water events.

To date, controlling it rivals Egyptian pyramid construction in labor intensity.

The work of controlling knotweed is tiresome but provides considerable job security, National Park Service biologist Jamie Myers said.

Myers said she spoke at the May 1 meeting of the Upper Delaware Council not so much to define the plant, but to provide advice about dealing with it.

While its fleshy stalks can be baked in a cobbler, similar to rhubarb, and it will also produce a serviceable wine, knotweed stalks are really better left to trimming shears and drying containers. It needs to be carefully disposed of because it reproduces so readily. “Pieces of the plant as small as your fingernail can reproduce,” Myers said.

Its roots won’t hold soil against flooding, but they are carried off during flooding, further spreading the plant.

Chemical controls are available, but involve expensive injection tools to treat individual stalks.

Knotweed can also be controlled by covering it with plastic sheeting, but up to two years of covering is recommended.

For now, Myers said repeated and careful cutting during its growth season is the recommended control measure. Cuttings need to be dried away from soil before disposal or burning.

UDC Chair Andrew Boyar said the Town of Highland has apparently had success in repeated cutting on one section of shoreline in the town.

There may be better biological methods on the horizon. Myers said the British have been successful in controlling knotweed with a species of plant lice. The U.S. Agriculture Department has not approved introduction of the insect into the U.S. Myers called the lice control “a glimmer of hope.”

For more, visit www.cabi.org/isc/datasheet/23875.