Effects of integrated management for invasive sericea lespedeza (Lespedeza cuneata) control in the tallgrass prairie: Fire, herbicide, grazing, and the role of germination timing and shade on spread and survival

Invasive species are a global threat, serving as the second leading cause of reduced biodiversity and costing over 1 billion dollars annually. In the tallgrass prairie, one invasive species is especially damaging: sericea lespedeza (Lespedeza cuneata). While others have explored the use of fire and herbicide to control sericea, large-scale, replicated experiments using regionally standard management techniques like whole pasture burning and grazing are lacking. Moreover, additional research is needed to assess how shading and freezing temperatures affect sericea seedlings and explain some potential mechanisms for effective control methods. We conducted a large-scale field study and two greenhouse experiments to assess how fire, herbicide, shade, and seedling age at first frost affect sericea spread and survival. Specifically, we burned six large, grazed pastures (> 350 ha) and treated portions of each with fall applications of metsulfuron-methyl to assess how burn season, timing of herbicide application, and seasonal grazing by yearling stocker steers affect sericea cover and seed production in the Flint Hills of Oklahoma. Additionally, we designed two greenhouse experiments to test the effect of seedling age at first frost on over-winter survival and the effect of shade on the growth and survival of sericea seedlings. Sericea cover varied with burn season, with sericea cover increasing or staying the same after a dormant season burn but decreasing or staying the same after a growing season burn. We observed the greatest sericea control with a late growing season fire (August) followed by a metsulfuron-methyl application 13.5 months after the burn, which resulted in a 30% reduction in upper canopy sericea cover (< 1% cover post-treatment) and reduced seed production (64 seeds/stem). Sericea cover and seed production were lower in the sprayed treatments than in the unsprayed controls, regardless of burn season. Likewise, over-winter survival and above and below-ground biomass were lower for sericea seedlings germinating in September than those germinating in June. Shade also negatively impacted sericea seedling growth, with shaded seedlings exhibiting lower above and below-ground biomass than unshaded seedlings. These findings highlight the potential role of growing season fire, herbicide applications, and shading for sericea control.