Evaluation of glufosinate tank mixes with glyphosate and imazapyr for cogongrass ( <i>Imperata cylindrica</i> ) control in natural areas

Abstract Cogongrass [ Imperata cylindrica (L.) P. Beauv.] is a recalcitrant invasive grass widespread in the southeastern United States. In non-crop systems, management relies on foliar applications of glyphosate and imazapyr; multiple applications over several years are often required, increasing labor, logistical, and chemical costs. Although numerous herbicide alternatives have been evaluated, few match the efficacy of glyphosate or imazapyr. Glufosinate is a broad-spectrum herbicide, and demand for glyphosate alternatives has generated interest in its potential for invasive grass management, but long-term evaluations of glufosinate and tank mixes for I. cylindrica are limited. This study evaluated single foliar spot applications of glufosinate (2.0 kg ae ha −1 ) alone and in tank mixtures with glyphosate (3.4 kg ae ha −1 ) or imazapyr (1.1 kg ae ha −1 ) at three Florida field sites heavily invaded (88% to 92% cover) by I. cylindrica using percent cover and belowground biomass. All treatments containing glufosinate produced rapid foliar necrosis, reducing cover to 15% to 21% within 14 days after treatment (DAT). By 270 DAT, cover increased in the glufosinate-alone (43%) and glufosinate + glyphosate (42%) treatments but remained approximately 25 to 30 percentage points lower than the control. At 540 DAT, cover in these treatments did not differ from that in the control. Across all sites, I. cylindrica cover at 540 DAT was reduced relative to the control by glyphosate (37%), imazapyr (9%), imazapyr + glufosinate (7%), and imazapyr + glyphosate (11%). Notably, the imazapyr + glufosinate mixture produced both rapid and sustained reductions in I. cylindrica cover. These results suggest glufosinate alone provides short-term suppression of aboveground tissue but can be enhanced through tank mixing with soil-active herbicides such as imazapyr to improve long-term suppression of belowground meristems.