Effectiveness of integrating mowing and systemic herbicides applied with a weed wiper for Sporobolus indicus var. pyramidalis management in Florida

Sporobolus indicus (L.) R. Br. var. pyramidalis (P. Beauv.) Veldkamp is an invasive species in grasslands, and herbicide application has been the most efficient management method to suppress this weed. Experiments were conducted to determine the effects of wiping glyphosate and hexazinone on S. indicus var. pyramidalis in 2017 and 2018. A dose-response experiment using a hand-held weed wiper was established with twenty treatments comprising two herbicides (glyphosate and hexazinone), uni- and bi-directional wiping methods, and five herbicide concentrations (6.25, 12.5, 25.0, 50.0 and 100% v/v basis). Data were collected 30 and 60 days after treatment (DAT). An ATV-mounted roto-type weed wiper experiment was established in a strip plot arrangement with mowing as the horizontal strip, the wiping method (uni-directional vs bi-directional) randomized as the vertical strip with three dosages of each herbicide for a total of 12 wiping treatments. Data were collected 35 and 90 DAT. The percent plant mortality was calculated using differences in pre- and post-treatment plant counts. Analysis of variance (ANOVA) and log-logistic linear regression were used to analyze the data. The dose-response experiment showed that S. indicus var. pyramidalis mortality increased with herbicide concentration and mortality was greater with the bi-directional wiping method compared to the uni-directional method. Treatments wiped bi-directionally with glyphosate at 70% v/v, hexazinone at 30% v/v and hexazinone at 60% v/v, resulted in S. indicus var. pyramidalis mortality ranging from 75 to 98% by 90 DAT across all locations. The ATV-mounted weed-wiper experiment showed that mowing prior to herbicide application with weed-wipers decreased the efficacy of both herbicides. Overall, both experiments indicate that S. indicus var. pyramidalis should be wiped bi-directionally using either glyphosate (70% v/v) or hexazinone (at least 30% v/v) to obtain satisfactory control. Further work should be conducted to determine if seasonality impacts the response of S. indicus var. pyramidalis to mowing and the application of these herbicides.