Reducing non-target damage to native emergent plants when managing aquatic weeds

Abstract

Urban wetland restoration requires planting native species that are consistent with the existing regional ecosystem. These young wetlands are particularly prone to weed invasion due to ongoing urban disturbances, implying herbicides may be used for maintenance purposes later. This study evaluated the aquatic herbicide sensitivity of common emergent macrophyte species in Queensland to inform planting choices in wetland restoration areas. Six native emergent plant species commonly used for restoration were selected: Baumea articulata, Boboschoenus caldwellii, Lepironia articulata, Eleocharis acuta, Philydrum lanuginosum and Cyperus exaltatus. They were grown in outdoor ponds located in Brisbane, Australia. Replicated mature plants of each species were sprayed with three aquatic herbicides at various doses up to their maximum label rate: flumioxazin (0, 25, 50, 105, 210 g ai/ha), glyphosate (0, 360, 720, 1440, 2160, 3240 g ai/ha) and florpyrauxifen-benzyl (0, 2.5, 5, 10, 15, 30 g ai/ha). Five months after treatment, all plants were harvested above substrate level and the dry mass of remaining live matter weighed. Glyphosate was the most destructive of the three herbicides tested as it significantly reduced the dry mass or completely removed 4 of the 6 species, while flumioxazin affected only 1 species and florpyrauxifen-benzyl did not affect any of them. E. acuta was sensitive to both glyphosate and flumioxazin. P. lanuginosum and C. exaltatus were the least sensitive species with no significant differences between controls and any of the three herbicides tested. At the time of writing, florpyrauxifen-benzyl is not yet registered for aquatic use in Australia. Plants that are more resistant to currently registered products can be selected for wetland restoration. At established sites, non-target damage can be predicted, and a suitable herbicide selected to reduce damage. Ongoing management of weeds that 'hide' among emergents, e.g. salvinia, can be effective without sacrificing natives.