Cereal Rye May Be Best Cover Crop Choice

An article titled “Influence of Cover Crops on Management of Amaranthus Species in Glyphosate- and Glufosinate-Resistant Soybean” by Loux et al. [Weed Tech., Vol. 31:487-495, 2017] provides results from a fall 2013 through fall 2015 multi-state field study that was conducted at 13 sites in Arkansas, Indiana, Illinois, Missouri, Ohio, and Tennessee. The study was designed to determine the effect of cereal rye and either oats, radish, or annual ryegrass cover crops [CC] on the control of Amaranthus spp. when integrated into comprehensive herbicide programs for soybean. Study details and results follow.

•   Amaranthus species [includes Palmer pigweed] have become the major problematic HR weeds in soybean.

•   The study was conducted with known infestations of redroot pigweed, common waterhemp, and Palmer amaranth. The Palmer populations were resistant to glyphosate. Only results from the 6 sites that contained Palmer pigweed are presented here.

•   Two cover crops were used–either cereal rye or a second cover crop that varied by site and included annual ryegrass, spring oat, and forage radish, along with a no-cover crop treatment.

•   Herbicide treatments within each combination of cover crop and HR soybean trait [glyphosate-resistant (GR) and glufosinate-resistant (GLR) soybean varieties] were designed to provide a comprehensive approach for Palmer amaranth control. They were 1] PRE/POST that consisted of PRE flumioxazin [e.g. Valor, Panther SC] followed [fb] POST application of foliar and residual herbicides applied 21 days after planting [DAP], and 2] PRE/POST/POST that consisted of the same PRE herbicide fb by the same POST application of foliar and residual herbicides applied at 21 DAP and a POST foliar herbicide application at 42 DAP. A nontreated control was also included.

•   The first POST treatment consisted of glyphosate, fomesafen [e.g. Reflex, Flexstar], and metolachlor [e.g. Dual] applied to GR soybean, and glufosinate and metolachlor applied to GLR soybean. The second POST treatment in both the GR and GLR systems was acetochlor [e.g. Warrant].

•   Both herbicide programs effectively controlled [>92%] Palmer pigweed throughout the season regardless of whether or not a cover crop was present. In the absence of herbicides, cereal rye provided significantly more control [34 to 49%] of Palmer amaranth than the other cover crop species [<22%].

•   Palmer amaranth density was uniformly and equally low in both herbicide programs throughout the season regardless of cover crop presence or absence. Without herbicides, the cereal rye cover crop resulted in over 50% more weed density reduction than the other cover crops and a no cover treatment.

•   Soybean seed yield was highest from the herbicide treatments; there was no difference in yield between the herbicide programs or between cover crop treatments when herbicides were used. In the absence of herbicides, 24% greater soybean yield was obtained following the cereal rye cover crop vs. the other cover crops.

All of the above results indicate that cereal rye has a greater potential for controlling Palmer pigweed than the other cover crops used in this study.

Although cover crops did not affect Palmer amaranth control in the herbicide programs used in this study, the increased control potential of the cereal rye when used as a cover crop could result in improved control in high weed density situations or where adverse environmental conditions following herbicide application may reduce their effectiveness.

For more information about using cover crops in Midsouth soybean production systems, click here.

Composed by Larry G. Heatherly, Oct. 2017, larryheatherly@bellsouth.net