Influence of cover crops on management of Amaranthus species in glyphosate- and glufosinate-resistant soybean

Authors: LOUX, MARK - The Ohio State University; DOBBELS, KEVIN - The Ohio State University; BRADLEY, KEVIN - University Of Missouri; JOHNSON, WILLIAM - Purdue University; YOUNG, BRYAN - Purdue University; Spaunhorst, Douglas; NORSWORTHY, JASON - University Of Arkansas; PALHANO, MATHEUS - University Of Arkansas; STECKEL, LAWRENCE - University Of Tennessee

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2017
Publication Date: 8/1/2017
Publication URL: https://handle.nal.usda.gov/10113/5832862
Citation: Loux, M.M., Dobbels, K.W., Bradley, K.W., Johnson, W.G., Young, B.G., Spaunhorst, D.J., Norsworthy, J.K., Palhano, M., Steckel, L.E. 2017. Influence of cover crops on management of Amaranthus species in glyphosate- and glufosinate-resistant soybean. Weed Technology. 31:487-495.

Interpretive Summary: Fall planted cereal rye, oats, radish, and annual ryegrass cover crops that are terminated prior to planting soybean in the spring have the potential to influence control of Amaranthus species when used in combination with herbicides in glyphosate-resistant and glufosinate-resistant soybeans. The two herbicide programs studied were: two applications consisting of a PRE residual herbicide followed by POST application of foliar and residual herbicide (PP); or three applications consisting of PRE residual herbicide followed by POST application of foliar and residual herbicide, followed by another POST application of residual herbicide (PPP). At the end of the season, herbicides controlled 100 and 96% of the redroot pigweed and Palmer amaranth, respectively, versus 49 and 29% without herbicides, averaged over sites and other factors. The PP and PPP herbicide treatments controlled 83 and 90% of waterhemp at the end of the season, respectively, versus 14% without herbicide. The cereal rye controlled 34 to 49% of the Palmer amaranth over the season, while control did not exceed 22% for the other cover species or no cover. In the absence of herbicide, waterhemp control throughout the season did not exceed 19%. Averaged over other factors, soybean yield at the Palmer amaranth sites occurred in the order cereal rye > other cover species > no cover at 2820, 2280, and 1880 kg ha-1, respectively. Soybean yields at waterhemp sites were similar between the PP and PPP, and these were higher than the nontreated, with no differences among covers. At redroot pigweed sites, control, weed density, and soybean yield were affected only by herbicide treatment, with the control and yield lower in the absence of herbicides.

Technical Abstract: A field study was conducted from fall of 2013 through fall of 2015 to determine the effect of cereal rye and either oats, radish, or annual ryegrass on the control of Amaranthus spp. when integrated with comprehensive herbicide programs in glyphosate-resistant and glufosinate-resistant soybean. The two herbicide programs studied were: two applications consisting of a PRE residual herbicide followed by POST application of foliar and residual herbicide (PP); or three applications consisting of PRE residual herbicide followed by POST application of foliar and residual herbicide, followed by another POST application of residual herbicide (PPP). At the end of the season, herbicides controlled 100 and 96% of the redroot pigweed and Palmer amaranth, respectively, versus 49 and 29% in the absence of herbicides, averaged over sites and other factors. The PP and PPP herbicide treatments controlled 83 and 90% of waterhemp at the end of the season, respectively, versus 14% without herbicide. Cover species affected control of waterhemp and Palmer amaranth and soybean yield, only in the absence of herbicides. The cereal rye controlled 34 to 49% of the Palmer amaranth over the season, while control did not exceed 22% for the other cover species or no cover. In the absence of herbicide, waterhemp control throughout the season did not exceed 19%. Averaged over other factors, soybean yield at the Palmer amaranth sites occurred in the order cereal rye > other cover species > no cover at 2820, 2280, and 1880 kg ha-1, respectively. Soybean yields at waterhemp sites were similar between the PP and PPP, and these were higher than the nontreated, with no differences among covers. At redroot pigweed sites, control, weed density, and soybean yield were affected only by herbicide treatment, with the control and yield lower in the absence of herbicides.