Restoring native vegetation in a Eurasian water-milfoil dominated plant community using the herbicide triclopyr

Published source details Getsinger K.D., Turner E.G., Madsen J.D. & Netherland M.D. (1997) Restoring native vegetation in a Eurasian water-milfoil dominated plant community using the herbicide triclopyr. Regulated Rivers-Research & Management, 13, 357-375.
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Summary

Action: Use herbicide to control problematic plants

A replicated, controlled, before-and-after study in 1991–1993 in a river in Washington, USA (Getsinger et al. 1997) reported that applying herbicide to plots invaded by Eurasian watermilfoil Myriophyllum spicatum increased native macrophyte abundance and richness 1–2 years later, with no clear effect on overall macrophyte biomass. Results summarized for this study are not based on assessments of statistical significance. Before applying herbicide, treated plots contained 270–290 g/m² total macrophyte biomass (watermilfoil: 240–250 g/m²; native: 30–40 g/m²). Watermilfoil occurred in 89–94% of surveyed transect segments and native macrophytes in 57–70%. There were 1.8–2.1 plant species/m (native: 0.9–1.1). After four weeks, treated plots contained only 10–20 g/m² total macrophyte biomass (watermilfoil: <5 g/m² biomass; native: 10–20 g/m²). After 1–2 years, total macrophyte biomass had returned to pre-treatment levels (200–510 g/m²). Watermilfoil remained less abundant (biomass: 0–130 g/m²; frequency: 25–78%). Native macrophytes were more abundant than before treatment (biomass: 180–430 g/m²; frequency: 94–99%). There were 2.6–3.4 plant species/m (native: 2.1–2.5). In an untreated plot, abundance and richness remained at similar levels throughout the study. Any differences were typically opposite to, or smaller than, those in treated plots (see original paper for data). Methods: In August 1991, two 4–6 ha plots of milfoil-dominated vegetation in the Pend Oreille River were treated with herbicide (Garlon® 3A, injected 30–60 cm below water surface). One plot was in a side channel and one was in a sheltered cove. A third 2-ha plot in the side channel was left untreated. Submerged macrophytes were surveyed along four 100-m transects/patch before intervention (August 1991) and for up to two years after (September 1991–August 1993). Biomass was collected from four 0.1-m² quadrats/transect, then dried and weighed. Species presence was recorded in each 1 m segment of the transects.