Lessons from a decade of lake management: effects of herbicides on Eurasian watermilfoil and native plant communities

Abstract

Abstract. Eurasian watermilfoil (Myriophyllum spicatum) is a non-native and invasive aquatic macrophyte with a broad North American distribution. It can have significant negative effects on invaded waterbodies, including decreased native macrophyte diversity, formation of recreational nuisances, and lowered lakefront property values. Previous research suggests that M. spicatum decreases in response to herbicide treatment, but most studies are spatially and temporally limited, usually focusing on a single waterbody for a single year. The long-term effects of herbicides remain relatively unknown. Here, we share the results of an 11-yr observational study of aquatic macrophyte diversity, dynamics, and response to herbicide treatment on 28 Wisconsin lakes (15 of which were adaptively managed with herbicide for M. spicatum and 13 of which acted as unmanaged reference lakes). We found that overall, adaptive management decreases M. spicatum abundance over time, but that the efficacy of individual herbicide treatments can vary. We also found that lakes with relatively new M. spicatum populations (discovered within the last decade) treated smaller areas with lower frequency than lakes with established populations, and were able to maintain lower M. spicatum abundance. This suggests that using adaptive, science-based aquatic plant management strategies, including early detection and response, may increase invasive species management success. Finally, we show that the effect of herbicide treatment on native macrophytes is variable and can be significant. Overall, our results suggest that while herbicide treatment can be an effective adaptive management tool, particularly in lakes with relatively recent M. spicatum invasions, the specific effects of individual treatments can be unpredictable. This study allows lake stakeholders to better understand the efficacy of herbicide treatment, in addition to the possible non-target effects on native macrophyte species.

Constraining invader dominance: Effects of repeated herbicidal management and environmental factors on curlyleaf pondweed dynamics in 50 Minnesota lakes

“…Aquatic invasive species are one of the primary causes of degradation of freshwater ecosystems (Gallardo, Clavero, Sánchez, & Vilà, ), and aquatic invasive plants cause significant ecological and economic impacts (Hussner et al, ). Over $100 million is spent annually on control of aquatic invasive plants in the U.S.A. (Pimentel, Zuniga, & Morrison, ), yet the ability of those efforts to meet management goals is often uncertain (Abella, ; Kujawa et al, ; Nault et al, ).…”

“…how to best design a control plan for multi‐year reductions, or how winter conditions will mediate control effectiveness), arise at least partly due to research on CLP biology and management having mainly comprised small‐scale and case studies. Integration and analysis of larger datasets across greater spatial and temporal scales would allow more robust inferences and generalisations to be made (Frater et al, ; Kujawa et al, ; Nault et al, ). Even if implementing treatments based on existing science, managers face challenges such as variable outcomes (Kujawa et al, ), uncertainty regarding best practices (Hussner et al, ), and a lack of coordination and sharing of accumulated data and knowledge (c.f.…”

“…Even if implementing treatments based on existing science, managers face challenges such as variable outcomes (Kujawa et al, ), uncertainty regarding best practices (Hussner et al, ), and a lack of coordination and sharing of accumulated data and knowledge (c.f. Kujawa et al, ). Retrospective analysis of monitoring data collected during management of aquatic invasive plants offers a means to address these gaps (Heger et al, ).…”

“…Retrospective analysis of monitoring data collected during management of aquatic invasive plants offers a means to address these gaps (Heger et al, ). Such data can be collated and analysed to evaluate management practices at broader scales to advance understanding and practices (Fleming & Dibble, ; Frater et al, ; Heiskary & Valley, ; Hussner et al, ; Kujawa et al, ; Valley & Heiskary, ).…”

“…Because of variation in management strategies used, broadscale analyses also enable the efficacy of alternative management approaches to be compared (e.g. variation in the timing of first management interventions relative to initial invasion (Kujawa et al, )).…”