Effects of uncrewed aerial vehicle–applied triclopyr plus fluroxypyr rates on weeds and desirable forbs in Kansas tallgrass prairie

Abstract

We studied the impacts of uncrewed aerial vehicle (UAV)‐applied triclopyr + fluroxypyr on rangeland weeds and other forbs in native tallgrass prairie. Two rates were tested: high (0.63 kg ae ha ⁻¹ triclopyr + 0.21 kg ae ha ⁻¹ fluroxypyr) and low (0.21 kg ae ha ⁻¹ triclopyr + 0.07 kg ae ha ⁻¹ fluroxypyr). We evaluated injury to established plants (Baldwin's ironweed [ Vernonia baldwinii Torr.], goldenrod [ Solidago spp.], leadplant [ Amorpha canescens Pursh], western ragweed [ Ambrosia psilostachya DC.], and white sagebrush [ Artemisia ludoviciana Nutt.]) and potted seedlings (alyssum [ Lobularia maritima (L.) Desv.], Baldwin's ironweed, common evening primrose [ Oenothera biennis L.], common milkweed [ Asclepias syriaca L.], and sericea lespedeza [ Lespedeza cuneata (Dum. Cours.) G. Don]). For established plants, herbicide treatments did not impact percentage cover of individual species, although they did marginally increase the rate of decline in total forb cover ( p  = 0.05). The high herbicide rate increased the rate of increase in visual injury in all species ( p  < 0.05). For seedlings, visual injury was observed at both herbicide rates for Baldwin's ironweed, common milkweed, and sericea lespedeza ( p  < 0.01). Water‐sensitive papers revealed low and variable levels of spray coverage with apparent drift onto control plots. Normalized difference vegetation index slightly increased over time in the control treatment, whereas it decreased over time at the low herbicide rate and especially the high herbicide rate ( p  < 0.001). Advances in UAV technology will continue to promote spraying and sensing applications in rangeland environments, although the potential for nontarget impacts should be incorporated into management guidance.