Not knotweed!

Educating public about invasive species

By SANDY LONG

HONESDALE, PA — Chop it, burn it, dig it, douse it with chemicals and you still might not eradicate one of the Upper Delaware region’s most prolific invasive species—Japanese knotweed. Three agencies joined forces last week in presenting a detailed program devoted to the history, impacts and management of such invasive species impacting the region.

With a small crowd gathered in the parking lot of the Stourbridge Professional Complex in Honesdale, employees of the National Park Service and Wayne and Pike County conservation districts began with an overview of invasive species of various origins—aquatic, terrestrial, insects and pathogens.

Though the region is beset with many invasives, such as gypsy moths, purple loosestrife, American chestnut blight, hemlock woolly adelgid and didymo, an invasive algae now documented in the East, West and main stem of the Delaware River, the program focused primarily on Japanese knotweed, one of the most successful of the invasive plants, which outcompetes native species for resources.

Knotweed thrives in riparian, or streamside, habitats, where it creates extensive monocultures that prevent plant diversity by inhibiting the growth of native species that normally help to stabilize banks and reduce erosion. The resulting increase in sedimentation can seriously impact macroinvertebrate populations, which then disrupt the food chain, according to biologist Jamie Myers of the National Park Service.

The plant propogates most effectively through underground rhizomes along its root system, which can spread 60 feet from its point of origin. But the stalk can also generate new plants and a smaller percentage arises from its seeds. According to Myers, digging the plants’ roots without complete removal can result in helping to propagate it. “A piece of underground plant as small as a pinky can generate a new plant,” she said.

The resilient plant is unwittingly propagated by road crews when it is cut down and left to lie. Landscaping and construction activities can also transport it to new locations when it is carried in soils or fill.

Myers and Nick Spinelli, Pike County Conservation District watershed specialist, described the advantages and disadvantages to various control and eradication methods, then showed the results of each method on plots at the site.

Manual removal and burning target specific species, but are time and labor intensive. Due to the high water content of Japanese knotweed, plants removed by cutting must be placed on plastic tarps to permit drying before being burned completely. Recent research with clear plastic tarps placed atop areas where plants have been cut to the ground shows promise for chemical-free management, though it is not likely to result in permanent eradication. Once cleared, the area should be immediately replanted with native or non-invasive plants.

Chemical options such as glyphosate (commonly known as Roundup for land applications and Rodeo for applications in riparian zones) are generally highly effective but can contaminate soil and water or place humans or wildlife at risk. As if to illustrate this point, one such incident occurred during the demonstration when a backpack-style spray applicator being operated by Spinelli malfunctioned and doused the young man, clad in protective gear and eyewear, with a solution containing 8 percent Rodeo herbicide.

While some chemicals can be selectively applied, such as root baths for treatment of hemlock woolly adelgid, others, like foliar application, result in indiscriminate killing within the spray zone. One option allowing for improved control of Japanese knotweed is the injection of herbicide into the plant’s stalk using a specially designed gun-like tool that uses less herbicide with greater control of application. Tom Zetterberg, vice president of the Lackawaxen River Conservancy, said that the organization is looking into purchasing an injection tool and establishing several test plots along the Lackawaxen River.

Potential biological controls are currently under development, though are not expected to be available for five to seven years, according to Myers.

One surprising outcome of Myers’ work with invasive species has been the discovery that teens love to tackle the tenacious plant. She encouraged everyone to get involved in invasive species management and to support educational efforts to increase awareness. For more information contact Myers at 570/729-7842 or visit www.invasivespeciesinfo.gov/ or invasiveplants.net/ or tncweeds.ucdavis.edu/.