2003 Newman Lake Monitoring  - Fall Treatment

Description of Site

Newman Lake is a 1,200-acre lake located approximately 20 miles northeast of the city of Spokane. Eurasian watermilfoil (Myriophyllum spicatum) was discovered in Newman Lake in 2002. A September 2002 boat survey showed that Eurasian watermilfoil was contained in an area at the south end of the lake near the lake outlet. The goal of this project was to take immediate action to remove the existing milfoil in Newman Lake using 2,4-D, followed by diver hand pulling and other appropriate control techniques. Although great efforts have been taken to improve the water quality in Newman Lake, the lake is on the 303(d) impaired waterbody list. This lack of water clarity may hinder effective diver hand pulling efforts and increase the reliance on aquatic herbicides to control this infestation of milfoil.

2003 Late Fall Treatment

Selected areas in Newman Lake were treated with 2,4-D (AquaKleen) on October 21, 2003. The reason for the late application was to retreat plants that appeared to have recovered from the summer treatment and to treat missed plants. Because the plants appeared green and actively growing and the weather was warm (high 70’s and sunny), a decision was made to apply herbicides in the fall. A total of four acres were treated in four different areas of the lake. The herbicide was applied using a granular blower at a rate of 100 pounds per acre by a licensed applicator.

Although Ecology did not require herbicide samples to be collected during this treatment, County staff chose to do so. Herbicide residue samples were taken inside and outside of two treatment sites by Spokane County staff at a 1.5-acre site near the Fish and Wildlife boat launch and a 2-acre site near the lake outlet (see map). The water depth in the boat launch site was between five to ten feet. The water depth at the outlet site was about three to six feet. Samples were analyzed by the Cerexagri Laboratory using an ELIZA test. At all times, the herbicide residue concentrations were below the EPA drinking water standard for 2,4-D (70 ppb).

Efficacy: Because this was a late season treatment, efficacy could not be determined. Surveys in spring 2004 should provide a better idea if this treatment as effective.

Summary of 2,4-D (AquaKleen™) Residues from Newman Lake

Data from the Boat Launch Treatment Site
 

Time

Inside Treatment Site (ppb)

100 m outside (ppb)

200 m outside (ppb)

Pre (surface)

1.0

-

-

4 hours (surface)

34.8

-

-

7 hours (surface)

1.8

-

-

3 days (surface)

1.1

-

-

3 days (1 foot above bottom)

21.4

3.0

8.0

7 days (surface)

3.3

-

-