Submitted to: Weed Biology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2004
Publication Date: 10/1/2004
Citation: Molin, W.T., Hirase, K. 2004. Comparison of commercial glyphosate formulations for control of prickly sida, purple nutsedge, morningglory and sicklepod. Weed Biology and Managment. 4:136-141. Interpretive Summary: The activity of alternative glyphosate mixtures was investigated to determine whether improved weed control could be obtained by application of new formulations. This research was conducted at SWSRU, Stoneville, MS. An acidic, non-salt formulation of glyphosate (Engame) was found to have two to four fold greater efficacy than standard salt formulations of glyphosate (Roundup Ultra and Touchdown). This research shows that glyphosate formulations can be further improved which can result in improved activity thereby potentially reducing pesticide costs to the farmer.
Technical Abstract: The efficacy of the commercial glyphosate [(N-phosphonomethyl) glycine] formulations, Roundup Ultra, Touchdown, and Engame, were compared for control of prickly sida (Sida spinosa L.), morningglory (Ipomeae hederacea var. integriuscula Gray), sicklepod (Senna obtusifolia L.) and purple nutsedge (Cyperus rotundus L.). Engame is a new formulation of glyphosate that contains glyphosate acid and AMADS (1- aminomethanamide dihydrogen tetraoxosulfate), a proprietary mixture of sulfuric acid and urea, rather than glyphosate salt and surfactants. Injury from Engame differed from Roundup Ultra and Touchdown in that necrotic lesions formed on leaves several hours after treatment. Leaves of very susceptible species, such as prickly sida, were rapidly, though incompletely, desiccated and then became chlorotic and died in a manner typical of other glyphosate formulations. Engame was 2 to 3 times more active on growth inhibition than either the Roundup Ultra or Touchdown formulations based on GR50 comparisons expressed on an acid equivalent basis. GR50 estimates did not change over the three-week evaluation period for prickly sida and purple nutsedge, and after 2 WAT for morningglory. The GR50 estimates for sicklepod decreased over the three-week evaluation period indicating a slower response to glyphosate. AMADS applied alone caused minute necrotic lesions on sicklepod and purple nutsedge, and lesions up to 3 mm in diameter on prickly sida and morningglory. Further injury from AMADS was not noted and plants resumed growth without apparent delay. At rates above 1120 g ha-1, greater than 80% control was achieved at 7 DAT. These results demonstrated that glyphosate efficacy may be further enhanced by formulations that apparently improve uptake and/or translocation.