Signs of hope in flowering rush fight
SANDPOINT — Glimmers of hope continue to shine in the gloomy, windswept world of flowering rush.
The invasive aquatic weed has been spreading through the Pend Oreille basin since 2007 and vexing state and local resource managers because effective treatment methods have been elusive.
The only effective method of controlling the pernicious weed so far is pulling them by hand when plants are exposed in the winter drawdown of Lake Pend Oreille. It’s slow and laborious, but effective.
Tom Woolf, aquatic plants manager for the Idaho State Department of Agriculture, worked with a crew of hardy volunteers through a steady drizzle on Friday to carefully exhume flowering rush plants and their easily fragmented rhizomes.
Volunteers have been pulling the weeds by hand at City Beach’s swim areas for years and Woolf said the effort has made a difference. Woolf said hand-pulling has kept those areas from overrun by the prolific weed.
"It would have taken over," Woolf said.
There were 400 acres of flowering rush in the Pend Oreille as of early 2015. The plants have the ability to fill in bays with impenetrable tangles of weeds. Flowering rush also breeds swimmer’s itch, a bacteria carried on snails that are drawn to the plants.
It’s believed that flowering rush spread into the basin via Montana’s Flathead Lake. The plant is a native of Africa, Asia and Europe and was likely introduced in North America as an ornamental garden plant.
Flowering rush has shrugged off herbicide treatments in the Pend Oreille. But a treatment method developed by Bonner County Noxious Weed Superintendent Brad Bluemer continues to show great promise — so much so that it’s caught the attention of leaders in the field of noxious weed research and the U.S. Army Corps of Engineers’ Engineer Research & Development Center.
Bluemer began experimenting with the use of off-season, dry-ground herbicide applications on private property last year and discovered they were effective in killing flowering rush. Bluemer suspected in-season herbicide applications were ineffective because sunlight would photodegrade the herbicide.
"Sunlight degrades almost all herbicides," said Bluemer.
Bluemer said his initial testing with a Imazapyr, a non-selective, broad-leaf herbicide killed 95 percent of the flower rush on 13 acres that were tested. Treatments were most effective when they were coordinated with rain events because the moisture helps the herbicide reach the plants’ root structure.
"We were really pleased and extremely excited," said Bluemer.
The success of the pilot project has drawn in John Madsen, a research biologist with U.S. Department of Agriculture and Kurt Getsinger, a research biologist at ERDC. Scientific research using variations of Bluemer’s method is now being conducted on 16 quarter-acre plots in the Clark Fork Delta.
Bluemer said the testing will be conducted over the next three years and he’s grateful for the corps’ involvement.
"This could be the answer for managing those infestations for decades to come, to keep it from completely filling in the bays," said Bluemer.
Woolf is also hopeful the testing will ultimately certify the treatment method as viable.
"We’ve never really had any data to fall back on, but now it’s looking good," said Woolf.