Field application of florpyrauxifen-benzyl to treat hybrid Eurasian watermilfoil: initial effects on native and invasive aquatic vegetation

Abstract

One of the most widespread and common invasive aquatic plant species in North America is Myriophyllum spicatum L. (Eurasian watermilfoil). Given the variety of impacts it has on ecological and recreational values, identifying an effective treatment strategy for Eurasian and hybrid watermilfoil is a priority for invasive aquatic plant management agencies. Unfortunately, traditional control efforts using herbicides have not only been variably effective, but they have also resulted in non-target impacts. The herbicide florpyrauxifen-benzyl (trade name ProcellaCOR®) has recently been approved but understanding of effectiveness is mostly limited to mesocosm studies. Our study reports the outcome of using florpyrauxifen-benzyl to treat a strain of hybrid watermilfoil in an inland lake in the Laurentian Great Lakes region. Mean abundance in treatment areas decreased at all points sampled (or stayed the same where initial cover was zero). Percent cover in the two quadrats declined from 50% to 5% in area 1, and 20% to 0% in area 2. Of the nine native plant species present, frequency of occurrence increased (six species) or stayed the same (three species) after treatment. Mean species richness at each transect increased pre-to post-treatment. The substantial decreases in this strain of hybrid watermilfoil abundance and increases in presence of native aquatic vegetation in this field study provide initial evidence that florpyrauxifen-benzyl is effective in partial-lake treatments of this strain of hybrid watermilfoil at an application rate of 12.68 oz/ac ft, with limited non-target impacts to native species. Our study balances observational studies with logistical management concerns to benefit researchers and lake stakeholders, alike. Study outcomes support recent advances in milfoil management that could lead to improved control, which translates to reduced ecological and recreational impacts of milfoil, as well as reduced non-target impacts and long-term management costs.