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ARS Home » Southeast Area » Tifton, Georgia » Crop Protection and Management Research » Research » Publications at this Location » Publication #256379
Title: Herbicide Effect on Napiergrass (Pennisetum purpureum Schum.) Control

Author
item CUTTS, G.S. - University Of Georgia
item GREY, T.L. - University Of Georgia
item VENCILL, W.K. - University Of Georgia
item Webster, Theodore
item LEE, R.D. - University Of Georgia
item TUBBS, R.S. - University Of Georgia
item Anderson, William - Bill

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2010
Publication Date: 3/1/2011
Citation: Cutts, G., Grey, T., Vencill, W., Webster, T.M., Lee, R., Tubbs, R., Anderson, W.F. 2011. Herbicide Effect on Napiergrass (Pennisetum purpureum Schum.) Control. Weed Science. 59(2):255-262.

Interpretive Summary: The Energy Independence and Security Act of 2007 requires 136 billion L of renewable biofuels be consumed by 2022, with 79 billion L mandated to originate from advanced biofuels (i.e. ethanol made from sugar, cellulosic materials, hemicelluloses, lignin, and starch are advanced biofuels). A perennial grass, napiergrass produces high biomass yields. In lower latitudes of the US, napiergrass is a weedy species. In the tropics, some consider napiergrass an invasive weed due to its rapid growth and perennial nature. Studies were initiated to evaluate the influence of herbicides for control of established stands of napiergrass. Autumn treatment of glyphosate caused severe napiergass injury, while injury due to imazapic was less. Hexazinone initially stunted napiergrass growth, but injury was undetectable at 50DAT. Differences in napiergrass response to glyphosate between locations (92% vs <30%) with sequential autumn and spring treatments was observed. In spite of these differences, ultimately sequential autumn and spring glyphosate treatments failed to eradicate napiergrass, as did imazapic. Spring-only treatments of glyphosate had no visible signs of napiergrass injury at 34DAT. The sole spring treatment with potential for controlling napiergrass was imazapyr, but rate of application was high and needs to be evaluated at lower rates. Further field-based weed control scenarios need to be studied before large scale production of napiergrass for a biofuel feedstock can begin in Georgia and the southeast US.

Technical Abstract: The interest in napiergrass as a renewable cellulosic bio-feedstock for energy production raises concerns with potential methods of control for escaped plants and volunteer plants in successive crops. In greenhouse experiments, hexazinone, glyphosate, and imazapic were applied POST, and CO2 assimilation (An) and stomatal conductance measured. Hexazinone and glyphosate ceased An by 2 and 12 DAT, respectively. Imazapic reduced An to a constant rate, but did not reach zero. In field studies these herbicides were applied to established napiergrass stands. Autumn treatment of glyphosate caused severe napiergass injury (>84%), while injury due to imazapic was >75%. Hexazinone initially stunted napiergrass growth, however, injury was undetectable at 50DAT. Differences in napiergrass response to glyphosate between locations (92% vs <30%) with sequential autumn and spring treatments was observed. In spite of these differences, ultimately sequential autumn and spring glyphosate treatments failed to eradicate napiergrass, as did imazapic. Spring-only treatments of glyphosate had no visible signs of napiergrass injury at 34DAT. The sole spring treatment with potential for controlling napiergrass was imazapyr, but rate of application was high and needs to be evaluated at lower rates. Further field-based weed control scenarios need to be studied before large scale production of napiergrass for a biofuel feedstock can begin in Georgia and the southeast US.