Plant-eating insect takes a bite out of invasive knotweed

Chequamegon-Nicolet Blowdown Timber

This spring, the USDA Forest Service’s Morgantown Field Office helped launch the nation’s first experimental release of a biocontrol agent — a tiny plant-eating insect — in the fight against invasive knotweed. 

A Forest Health Protection team conducted releases of the Japanese knotweed psyllid (Aphalara itadori) at three West Virginia field sites, including New River Gorge National River and property north of Charleston. Previously, USDA APHIS extensively screened this non-native psyllid for possible adverse impacts and recently issued permits for release in the U.S. 

Knotweeds from eastern Asia — which have large leaves and can grow to over 10 feet — are invasive in the U.S. and Canada. They were introduced as ornamentals in the 19th century and were used for erosion control, but subsequently escaped cultivation. Currently, three types of invasive knotweeds are spreading in the northwest and northeast corners of the U.S. and creeping into the interior: Japanese knotweed (Fallopia japonica), giant knotweed (Fallopia sachalinensis) and hybrid Bohemian knotweed (Fallopia x bohemica, a cross between Japanese and giant knotweed). Like many invasive plants, knotweed is difficult to manage or eradicate once widely distributed, and infestations are expected to increase as average winter temperatures rise and the growing season lengthens.

But the Japanese knotweed psyllid promises to be a formidable match for this tough invasive plant. Psyllids feed on the sap of the knotweed, diminishing its energy supply and ultimately killing the plant. Researchers found that the Japanese knotweed psyllid’s preference is specific to the three targeted knotweeds, and it is not expected to damage any native or related knotweed family plants. Furthermore, this psyllid’s native climate in Japan is similar to West Virginia’s, suggesting that it may thrive in the area.

The biocontrol project will study whether the psyllid population at the release site becomes established and expands. Post-monitoring will assess how psyllids affect knotweeds at the site. Results will help determine whether the psyllid could be a biocontrol tool to manage the invasive knotweeds broadly in the U.S.

The Morgantown Field Office team leading the study includes plant pathologist Yun Wu, plant biologist Heather Smith and entomologist Chris Hayes. They are joined by Douglas Manning, National Park Service; Kristen Carrington, West Virginia Department of Agriculture; and Richard Reardon, Forest Service (retired).