Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2009
Publication Date: 9/9/2009
Citation: Reddy, K.N., Bryson, C.T. 2009. In-Crop and Autumn-Applied Glyphosate Reduced Purple Nutsedge (Cyperus rotundus)Density in No-Till Glyphosate-Resistant Corn and Soybean. Weed Technology 23:384-390.
Interpretive Summary: Purple nutsedge is a difficult to control weed because of prolific tuber production, ability of tuber to sprout several times, and the lack of herbicides to kill dormant tubers. In the southern US, corn and soybean are harvested beginning in August. The time between harvest and frost provides a favorable environment for purple nutsedge to re-establish and replenish tubers, sustaining future infestations. Scientists at Southern Weed Science Research Unit, Stoneville, Mississippi have conducted a 3-yr field study to determine efficacy of in-crop and fall-applied glyphosate on purple nutsedge population and yield of no-till Roundup Ready corn and Roundup Ready soybean. Glyphosate applied in the fall alone reduced purple nutsedge densities considerably in both corn and soybean grown under no-tillage system. Similarly, glyphosate in-crop applications also effectively reduced purple nutsedge densities in both crops. At the end of 3-yr study, both fall applied and in-crop applied glyphosate together provided 100% control of purple nutsedge. Corn is more competitive with purple nutsedge than soybean. These results demonstrated that fall applied glyphosate was effective in reducing purple nutsedge following harvest of crops and fall application of glyphosate could be an effective management strategy regardless of Roundup Ready crop.
Technical Abstract: A 3-yr field study was conducted from 2005 to 2007 at Stoneville, MS to determine efficacy of in-crop and fall-applied glyphosate on purple nutsedge density and yield of no-till glyphosate-resistant (GR) corn and GR soybean. Separate experiments were conducted in GR corn and GR soybean in areas maintained under no-tillage system after the fall of 2004. Each experiment was conducted in a split-plot arrangement of treatments in a randomized complete block design with and without fall application of glyphosate at 1.68 kg ae/ha as main plot and in-crop herbicide application (glyphosate- and nonglyphosate-based programs) as subplot with three replications. In GR corn, glyphosate applied in the fall reduced purple nutsedge density by 40 to 67% compared to no glyphosate during three years. In GR corn, glyphosate applied in-crop reduced purple nutsedge density by 48% in 2005, 92% in 2006, and 100% in 2007 compared with no herbicide. However, GR corn yields were unaffected by either in-crop or fall-applied glyphosate. In GR soybean, glyphosate applied in the fall reduced purple nutsedge density by 64 to 83% compared to no glyphosate during three years. Glyphosate applied in-crop in GR soybean reduced purple nutsedge density by 81% in 2005, and 100% in 2006 and 2007 compared with no herbicide. GR soybean yields were similar in 2005, but yields were 34 and 18% higher in 2006 and 2007, respectively, with fall-applied glyphosate compared to no glyphosate. GR soybean yields were higher with glyphosate applied in-crop compared with no herbicide in two of three years. These results indicate that purple nutsedge density could be reduced with glyphosate applied in-crop in no-till GR corn and GR soybean. In addition, fall-applied glyphosate was effective in reducing purple nutsedge populations following harvest of crops and could be an effective purple nutsedge management strategy regardless of GR trait.