CA dense mat-forming population of Eurasian watermilfoil
(
Myriophyllum spicatum
L
.
) was interfering with fishing and
recreation in a small western Washington lake. A low concentration
(1.5 mg/L active ingredient) of the herbicide endothall
formulated as Aquathol® K was used in 2000 to attempt
to selectively control the Eurasian watermilfoil. Aquatic plant
biomass and frequency data were collected before treatment,
ten weeks after treatment and during the growing season for
3 additional years. Macrophyte data were analyzed to assess
the herbicide’s impacts on Eurasian watermilfoil as well as
the rest of the aquatic plant community. Results showed a significant
decrease in Eurasian watermilfoil biomass and frequency
10 weeks after treatment. The Eurasian watermilfoil
continued to be present, but at a significantly reduced level
through the remainder of the study (3 years after treatment).
Of the native plant species, large-leaf pondweed (
Potamogeton
amplifolius
Tucker
.
) frequency and biomass was significantly
reduced after treatment. Common elodea (
Elodea canadensis
Rich.), muskgrass (
Chara
sp. Vallaint.) and bladderwort (
Utricularia
sp. L.) all increased significantly after treatment.
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