Wynn-dow of opportunity—reversing Wynn cassia dominance at Spyglass Research Station

Abstract

Maintaining a desirable grass–legume balance is critical for sustaining pasture productivity and livestock performance in northern Australian grazing systems. At Spyglass Beef Research Facility, Queensland, paddocks sown with buffel grass (Cenchrus ciliaris) and Wynn cassia (Chamaecrista rotundifolia) have substantially changed composition since 2021, with Wynn cassia increasing from approximately 40% to more than 80% of total standing dry matter (TSDM) in some areas. Following concerns about the potential loss of the grass component, a demonstration trial was established in 2026 to investigate potential contributing factors to Wynn cassia dominance and test some strategies for restoring a more desirable grass–legume balance. Pasture composition studies over 5 years were used to develop potential control interventions including small plot assessment of fluroxypyr herbicide at either 600 mL/ha or 1200 mL/ha applied to Wynn dominated pastures which were spelled from grazing. Biomass and botanical composition were assessed before treatment and again two months after application. All treatments resulted in a reduction in Wynn cassia contribution to TSDM and an increase in buffel grass biomass, but herbicide effects were modest (17-19% reductions in Wynn cassia contribution compared to 16% in the untreated plots). Total pasture biomass increased across all treatments. These preliminary results indicate that strategic herbicide application, combined with wet-season spelling, could potentially reduce Wynn cassia dominance and promote buffel grass recovery. Ongoing monitoring will determine the persistence of these responses and help define an optimal grass–legume balance for productive and resilient grazing systems on infertile tropical soils.