2018 ASHS Annual Conference

Ornamental grasses are popular in golf course natural areas and in landscapes due to their pest resistance and ability to thrive in low-input environments. While many grass species are naturally disease and or insect pest resistant, weed control continues to be a challenge for both landscape pest control operators and golf course superintendents managing large monocultures of native/ornamental grasses. Research was conducted in 2016 and 2017 in Apopka, FL to determine the response of 14 different ornamental grasses to over-the-top applications of topramezone, a new HPPD inhibiting herbicide. Uniform and fully-rooted liners were planted in the field and allowed 2 months to establish prior to treatment. At this time, topramezone was applied over-the-top to each species at rates of 0.05 and 0.10 kg ai ha^-1 using a CO₂ backpack sprayer. A sequential application followed 6 weeks later using the same rates. Species evaluated in 2016 included Schizachyrium scoparium ‘The Blues’ (little bluestem), Tripsacum dacyloides (eastern gamagrass), T. floridanum (florida gamagrass), Chasmanthium latifolium (wild oats), Muhlenbergia capillaris ‘White Cloud’ (white cloud muhlygrass), Eragrostis elliotti ‘Wind Dancer’ (wind dancer lovegrass), Panicum virgatum (Red switchgrass), and Spartini bakeri (sand cordgrass). Andropogon virginicus (broomsedge), Miscanthus sinensis ‘Purpurescens’ (purple miscanthus), little bluestem, Sorghastrum nutans (indian grass), Carex appalachica (Appalachian sedge), Muhlenbergia capillaris (muhlygrass), Eragrostis curvula (weeping lovegrass), and Pennisetum alopecuroides ‘Cassian’ in 2017. Data collected included visual injury ratings at 3, 7, 14, 28, and 42 days after the first and second treatment. In 2016, growth index [(plant height + plant width1 + plant width2)/3] was recorded and plant shoot dry weights were recorded in 2017.The trial was designed as a completely randomized block design and each species was considered a separate experiment. Eastern gamagrass, Florida gamagrass, and little bluestem showed no injury or growth reduction following either application. No injury was seen on broomsedge but a growth reduction was evident at both topramezone rates. Purple miscanthus and Indian grass showed a high degree of tolerance following one application but injury was observed following the second. Wind dancer love grass, wild oats, sand cordgrass, red switchgrass, cassian fountaingrass, pink muhly, white cloud muhly, and weeping lovegrass were severely injured at both rates following only one application. Results suggest there is potential for future use of tropramezone in and around certain ornamental grass species, but testing a small group of plants prior to large-scale application would be needed due to potential phytotoxicity.