AIP task force prepares for 2024 treatment

The Sanders County Aquatic Invasive Plants (AIP) IP Task Force oversees treatment of Eurasian Watermilfoil (EWM) in Noxon and Cabinet Gorge reservoirs each year. Last year, the task force treated a total of 109 acres of EWM infestations: 93 acres over seven plots in Noxon and 16 acres over three plots in Cabinet Gorge. “We used a combination of two contact herbicides: diquat and flumioxazin. This is the first year we’ve used flumi and did so at the suggestion of our Scientific Advisory Panel. Switching up the herbicides every so often helps prevent plants from developing resistance,” said Kim McMahon with the AIP task force. She said the injury assessment of EWM at six weeks post-treatment was 95% or better in eight plots and 90% in one plot. The last plot was too shallow to assess at the six-week timeframe.

The task force was able to treat about twice as much acreage in 2023 compared with prior years because of a $40,000 grant from the DNRC’s AIS grant program and because flumi costs less than the herbicide typically used by the task force. The AIS grant was matched by a $40,000 contribution from Avista’s Clark Fork Settlement Agreement, McMahon said.

In 2022, the task force treated 49 acres in Noxon and had an injury rate of 90% or better in seven of the eight treatment plots at six weeks post-treatment. In 2021, 64 acres were treated in Noxon with an injury rate of 95% or better in six of the seven treatment plots at six weeks post-treatment.

This year, FWP will survey the high priority access areas and make recommendations for treatments based on infestations they find during their assessment in mid-July. The task force will consider those recommendations amidst budgetary constraints and decide on treatments. The treatments will be visually assessed six weeks after treatment.

FWP will also conduct a reservoir-wide survey late this summer or early this fall. These surveys are done about every three years to provide a big-picture look at the status of aquatic invasive species (AIS) in the Noxon/Cabinet Gorge system. FWP does the annual monitoring in July and the periodic reservoir-wide monitoring as a contribution to the county program.

The task force has again applied for funding for herbicide treatments through CFSA ($40,000) and the AIS grant program ($40,000).

“While treatments have typically been conducted in early August due to a number of factors (water conditions being the main one), we are shooting for earlier treatments this year,” McMahon said. Projections are that runoff is likely to be on the low side, so the water will clear up sooner than usual which allows the plants to grow since sunlight can reach them. “Therefore, tentative plans are for FWP to survey the main access areas on Noxon and Cabinet Gorge in June so that we can get herbicide treatments done in early- or mid-July. If everything falls into place, EWM will be treated at access areas while the plants are actively growing but haven’t yet had an opportunity to grow into the upper areas of the water column. This means that they will be treated and die off before they become a nuisance,” she added. Additionally, the task force plans to use a systemic product – which is absorbed by the plant to kill the roots – that is also very successful at causing immediate die-off (as a contact herbicide would). This could give us greater control of EWM over a longer time period.

Another important task that the task force is taking on this year is review of the Management Plan. The current plan has been in place since 2018 and we are examining it to be sure it reflects actions of the Task Force and vice versa, McMahon stated.

In terms of education and outreach, AIS is a topic that is covered at the Green Mountain Conservation District’s annual “water festival” for elementary age kids, which is great, McMahon expressed. The task force will also incorporate AIS at the Plains sixth-grade campout this year.

McMahon said the task force has had several reports of algae blooms in the area in recent years. To report algae blooms or for more information, visit http://www.deq.mt.gov/water/programs/habs. More information about the local task force is available at http://www.sanderscountyais.com.