Response of four Vallisneria taxa to aquatic herbicides

Authors: Beets, Jens; HAUG, ERIKA - North Carolina Department Of Environmental Quality; SPERRY, BENJAMIN - Us Army Engineer Research And Dvelopment Center; THUM, RYAN - Montana State University; RICHARDSON, ROBERT - North Carolina State University

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Diverse communities of submersed aquatic vegetation are ecologically beneficial to aquatic ecosystems; however, nonnative plants commonly disrupt these communities and have associated benefits. Vallisneria species are recognized as desirable plants for aquatic resource managers. However, recent documentation of multiple non-native Vallisneria taxa in the United States has prompted concerns in aquatic systems management. Our primary objective was to evaluate the response of two native eelgrass species (Vallisneria americana and V. neotropicalis) and two nonnative taxa (V. australis and hybrid V. spiralis × V. denseserrulata) to common aquatic herbicide treatments in a small-scale mesocosm study. This research also provided efficacy data for new aquatic invasive taxa. Managers may control native and invasive Vallisneria taxa with endothall or combinations of endothall and diquat, endothall and florpyrauxifen-benzyl, and florpyrauxifen-benzyl and flumioxazin. Florpyrauxifen-benzyl alone does not provide nominal above or belowground biomass control compared to some of the other treatments tested. Fluridone reduced native V. americana above and belowground biomass but is less likely to suppress V. australis, V. neotropicalis, or V. spiralis × V. denseserrulata.

Technical Abstract: Greenhouse mesocosm experiments were conducted in 2023 to investigate herbicide efficacy on two native eelgrass species (Vallisneria americana Michx. and V. neotropicalis Vict.) and two nonnative taxa (V. australis S.W.L. Jacobs & Les and V. spiralis × V. denseserrulata Makino). Herbicide applications included endothall, diquat, florpyrauxifen-benzyl, fluridone, at select combinations of these herbicides. Endothall alone provided 90-100% aboveground biomass reduction at 3000 µg L-1 with at least 24 hours of continuous or intermittent exposure. Florpyrauxifen-benzyl applied alone resulted in minimal aboveground biomass reduction. Fluridone applied at 10 µg L-1 with 45 days of exposure resulted in 94.5% biomass reduction on V. americana and 7.1- -47.9% other tested taxa. The combination of flumioxazin and florpyrauxifen-benzyl resulted in 90-100% aboveground biomass reduction and endothall combined with florpyrauxifen-benzyl resulted in 93-100% aboveground biomass reduction. Reductions in belowground biomass mirrored trends observed in aboveground biomass. No selective treatments were identified between native and invasive Vallisneria taxa, although efficacy was observed on hydrilla bioindicator plants. These insights provide a basis of understanding for differences between these Vallisneria for researchers moving forward with selectively targeting hydrilla in the presence of native Vallisneria species and two new aquatic invasive plants. Future research should expand treatment and concentration exposure scenarios, increase the study period past six weeks, as well as identify potential integrated plant management strategies for field scenarios.