Publication Summary

An aquatic invasive non-native plant egeria (Egeria densa Planch.) in Battle Ground Lake (Clark County) was treated with the herbicide diquat in 2003. Plant community and water quality data were collected before treatment and up to three years after treatment. There was a significant reduction in egeria frequency and biomass after the herbicide treatment. The diquat spread throughout the lake and persisted at low levels in the water column for at least two weeks after treatment. There was a slight decrease in surface water dissolved oxygen and water transparency after the herbicide treatment due to increased algae growth.

A nearly monotypic population of egeria (Egeria densa Planch.) was interfering with recreation in a popular lake in Battle Ground State Park in southwest Washington. In June 2003 the littoral (shore) zone was treated with the contact herbicide diquat (6,7-dihydrodipyrido (1,2-a2′,1′-c) pyrazinediium dibromide).

Aquatic plant frequency and biomass data were collected on all submersed species before treatment, and eight weeks, one year, and two years after treatment. Water quality and herbicide dissipation data were collected before treatment and during the summer after treatment.

Results from the aquatic plant data showed a significant reduction in egeria frequency and biomass after the herbicide treatment, although the species did not disappear entirely. Two native submersed plants, water moss (Fontinalis antipyretica L.) and stonewort (Nitella sp Agardh.), and areas where submersed plants were absent, increased significantly after herbicide treatment.

The herbicide dissipation data showed that diquat spread throughout the lake and persisted at low levels in the water column for at least two weeks after treatment. Water quality data demonstrated a slight decrease in both surface water dissolved oxygen and water transparency after the herbicide treatment due to increased algae growth.