2-17498 p01-11 APMdj

The presence of Eurasian watermilfoil ( Myriophyllum spicatum L.) in aquatic systems has resulted in adverse impacts to native plant communities, ecosystem function, and water resource uses. Eurasian watermilfoil in Hayden Lake, Idaho, has spread rapidly, impacting the native plant community and recreational uses of the lake. Point intercept surveys were conducted to determine the current composition of the plant community and to assess the efficacy of triclopyr and 2,4-D herbicide treatments on Eurasian watermilfoil during the year of treatment. Twenty-two aquatic plant species were identified during four surveys (two of the littoral zone and two focused on herbicide treated areas) conducted between June and September 2007. The presence of Eurasian watermilfoil was reduced in all treated areas by 88% (p < 0.01) 5 weeks after treatment. There was no difference (p = 0.81) in the efficacy between triclopyr and 2,4-D for control of Eurasian watermilfoil. The use of herbicides had no significant deleterious impacts on the native plant community. The percent occurrence of large-leaved pondweed ( Potamogeton amplifolius Tuckerm.), Robbins’ pondweed ( Potamogeton robbinsii Oakes), and wild celery ( Vallisneria americana Michx.) increased after treatment (p < 0.01). Future triclopyr and 2,4-D applications should have minimal to no negative impact on the native plant community in Hayden Lake due to the dominance of monocotyledon species among the native vegetation, which are generally tolerant to these herbicides. 1 Geosystems Research Institute, Mississippi State University, Box 9652 Mississippi State, MS 39762-9652, USA. 2 Corresponding author, e-mail: [email protected]. Received for publication October 28, 2009 and in revised form December 22, 2009. 3 Idaho Department of Agriculture, P.O. Box 790 Old Penitentiary Rd., Boise, ID 83701. 4 Kootenai County Noxious Weed Control, 10905 N. Ramsey Rd., Hayden, ID 83835. 5 Current address: Great Gardens in North Idaho, 4221 Moccasin Rd., Coeur d’Alene, ID 83815.