Posted: Tuesday, March 05, 2013 10:01 AM
The Walla Walla County, Wash., Conservation District wants to eliminate the invasive weed false indigo, but a local beekeeper says the plant is beneficial to his honeybees.
Mike Denny, riparian habitat coordinator for the district, said this is the second season of spraying for the weed along the Touchet River.
The district uses water-compatible herbicides just as the plant begins to flower. The herbicide goes into the roots and kills the plant.
The weed is invasive and non-native to the region, Denny said. It was introduced along the Columbia River in the early 1970s to stabilize river banks, at the expense of the native plants, he said.
"It grows in a very narrow band and it is a legume, which means it sets nitrogen (with) its roots," Denny said. "It actually will acidify the soil, so nothing else can grow under it."
The plant grows in the band about a foot and a half above the water line.
"These are plants that can crank out 6,000 seeds at maturity," Denny said.
"It's been a major issue, especially as we continue to re-establish native riparian areas -- we're fighting this stuff all the time," he said.
The district is planting native riparian trees and shrubs along the river to keep out additional invasive weeds.
Mark McCubbins, a beekeeper and alfalfa seed farmer in Walla Walla County, said false indigo provides habitat for native honeybees. Removal of the weeds would destroy his spring buildup for bees, he said. He scatters 4,000 to 5,000 beehives along 40 to 50 miles, depending on the buildup and pollen to increase his bee numbers.
It's so hard to maintain bees, McCubbin said, "it would be terrible to lose any kind of forage."
McCubbins is also concerned about the impact of spraying on willow trees and river banks nearby, worrying that the banks will slough off into the water and cave in.
Denny said the willow trees are different species. False indigo competes against the willows and destroys them, he said. Willows are not sprayed, he said.
Denny said he doubts that the weeds are beneficial to bees. Some small native bees use them, but he's never seen a honey-producing bee use them, he said.
Denny also said farmers must sign access agreements to allow spraying.
The district received $64,000 in funding to eliminate the false indigo through the Conservation Reserve Enhancement Program from the USDA Farm Service Agency and other partners including the Confederated Tribes of Umatilla and the Washington Department of Ecology.