Planting green refers to no-till planting of the primary crop into actively growing cover crop. Cereal rye is the most commonly planted cover crop in corn/soybean cropping systems in Nebraska. Use of pre-emergence residual herbicide with multiple sites of action is one of the first recommendations for control of glyphosate-resistant Palmer amaranth. Additionally, to be effective, pre-emergence herbicide must be placed in contact with the soil and an even layer of the chemical is required to intercept germinating weed seeds. When pre-emergence herbicides are applied on standing cereal rye, it may affect the performance of the residual herbicides. Therefore, research is needed to determine performance of residual herbicides for control of Palmer amaranth when applied on standing cereal rye compared with cereal rye terminated before two weeks of planting soybean.

(1) To determine if planting soybean in standing cereal rye cover crop can suppress Palmer amaranth emergence better compared with early termination.
(2) To evaluate effect of planting green on performance of residual herbicides applied pre-emergence for control of glyphosate-resistant Palmer amaranth in soybean.
(3) Evaluate effect of early termination of cereal rye versus planting green on soil health, soybean yield, and cost-benefit ratio for economic analysis.

Field experiments will be conducted in a grower’s field infested with glyphosate-resistant Palmer amaranth near Carleton in Thayer County, Nebraska. Treatments will be arranged in a randomized complete block design (RCBD) with an augmented 2 x 12 factorial treatment arrangement with four replications. The augmented factorial treatment arrangement will include cereal rye termination timing (2 weeks before and after planting soybean) and 12 treatments, including three pre-emergence herbicides (Authority Supreme, Fierce MTZ, and Zidua PRO), post-emergence herbicides (Roundup PowerMax, XtendiMax), and a non-treated control, a weed-free control but cereal rye present, and a weed free and cereal rye free control. Palmer amaranth control, density and biomass will be measured and effect on soil health, yield, and cost-benefit ratio of each treatment will be calculated. An extension field day will be organized at the research site to demonstrate the results of the project to soybean growers and results will be presented during extension meetings and will be published in Crop Watch and NebGuide.

Updated May 19, 2023:

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Termination of cereal rye after 2 weeks of planting soybean suppressed weeds including Palmer amaranth and waterhemp better than terminating cereal rye 2 weeks before planting. This would be a good non-chemical tool to include in the toolbox for the effective management of herbicide-resistant weeds in soybean.

- Glyphosate-resistant Palmer amaranth is one of the most difficult to control weeds in soybean production. Several soybean growers in Nebraska have adopted planting green-- meaning planting soybean when cover crop such as cereal rye is standing.
- Results of this project will provide applied research based information to soybean growers if applying residual herbicides such as Authority Supreme, Fierce MTZ, or Zidua PRO in standing cereal rye can reduce their performance for management of glyphosate-resistant Palmer amaranth.
- Will answer questions such as if cereal rye cover crop is planted in fall, residual herbicides are needed or Palmer amaranth control can be achieved by using post-emergence herbicide such as dicamba.
- Results will provide best integrated Palmer amaranth management practices by including cereal rye cover crop and use of herbicides in Roundup Ready 2 Xtend soybean.