Response of Common Wildflower Species to Postemergence Herbicides

Wildflowers attract wildlife, increase pollinator habitat, and enhance the aesthetic value of the landscape. Wildflower establishment is increasingly part of an effort to reduce maintained turfgrass on golf courses, lawns, and other maintained en-vironments. Weed competition decreases wildflower establishment and results in poor long-term stands. Research was conducted in a controlled environment to investigate the tolerance of wildflower species to common postemergence herbicides. Wildflower species included California poppy (Eschscholzia californica Cham.), common sun-flower (Helianthus annuus L.), cornflower (Centaurea cyanus L.), garden coreopsis (Coreopsis lanceolata L.), partridge pea [Chamaecrista fasciculata (Michx.) Greene], plains coreopsis (Coreopsis tinctoria Nutt.), purple coneflower [Echinacea purpurea (L.) Moench], rosering gaillardia (Gaillardia pulchella Foug.), and violet prairie clover (Dalea purpurea Vent.). Herbicides evaluated were fluazifop at 0.28 kg center dot ha-1 a.i., meso-trione at 0.14 kg center dot ha-1 a.i., clopyralid at 0.29 kg center dot ha-1 a.i., bentazon at 0.56 kg center dot ha-1 a.i., halosulfuron at 0.053 kg center dot ha-1a.i., and imazaquin at 0.42 kg center dot ha-1 a.i. An untreated check was included for comparison. Excessive damage (z 53% phytotoxicity) was ob-served on all wildflower species in response to clopyralid, except for California poppy. Fluazifop and bentazon were relatively safe (5 19% phytotoxicity, regardless of her-bicide) on all wildflower species; however, bentazon resulted in z 40% aboveground biomass reduction in several species. Common sunflower and garden coreopsis were susceptible to halosulfuron (37% and 73% phytotoxicity, respectively) and imazaquin (37% and 87% phytotoxicity, respectively), but on all other wildflower species, phytotox-icity was 5 18%. Although both halosulfuron and imazaquin only resulted in 5 18% phytotoxicity to purple coneflower, a 43% to 44% aboveground biomass reduction was recorded. Mesotrione was only safe on California poppy and cornflower (5 11% phytotoxicity and 5 24% aboveground biomass reduction). Results suggest high tolerance variability across herbicides and species considered, but may prompt new investigation of safety and utility within field and production scenarios.