U.S. Army Corps of Engineers treating invasive flowering rush

Seattle District, USACE
Published April 1, 2024

To selectively manage the invasive weed flowering rush, U.S. Army Corps of Engineers (USACE) Albeni Falls Dam staff are performing herbicide treatments at six separate locations on dewatered portions of Lake Pend Oreille and Pend Oreille River.

The staff plan to treat the dewatered areas between April 8 and May 20 on up to 21 acres at the following USACE-owned locations: Riley Creek (up to 1 acre), Clark Fork Drift Yard (up to 1 acre), Hoodoo Creek Wildlife Management Area (~2 acres), Mallard Bay Wildlife Management Area (up to 1 acre), Oden Bay Wildlife Management Area (~8 acres), and the Pack River Wildlife Management Area (~8 acres).

They will treat the flowering rush with U.S. Environmental Protection Agency (EPA) and Idaho State Department of Agriculture (ISDA) approved herbicide isopropylamine salt of Imazapyr (Alligare), at application rates and concentrations allowed on the label.

Treatment timing selectively targets young flowering rush shoots, as this invasive plant breaks winter dormancy, before any non-target native vegetation begins to grow and will allow 14-days prior to springtime lake re-flooding of the flowering rush infested littoral zones.

The staff will not apply the herbicide in or over water.  Dewatered applications eliminate potential environmental impacts to water quality and non-target aquatic organisms because surface water is not present during the applications.

There are no fishing or swimming restrictions for any chemicals in the treated plots, and there are no restrictions on livestock consumption of water from the treatment areas after the herbicide applications.

For more information, contact Andrew Huddleston 208-437-3133 (Andrew.J.Huddleston@usace.army.mil), U.S. Army Corps of Engineers Albeni Falls Dam, 2376 East Highway 2, Oldtown, ID 83822, or Taylor Johnson 208-437-3133 (Taylor.M.Johnson@usace.army.mil).

As required by USACE-NWS’s EPA IPDES permit: Department of Environmental Quality’s (DEQ) regional Idaho State IPDES Compliance Officer Contact (Matthew Colling): 208-666-4639 and DEQ’s IPDES Pesticide General Permit from the (SERC) Application of Pesticides (IDG870000).

Andrew Huddleston

Release no. 24-008