Multi-tactic ecological strategies to manage Bassia scoparia and Amaranthus tuberculatus in the cropping systems of Great Plains and Midwestern U.S.

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Yadav, Ramawatar
Major Professor
Jha, Prashant
Liebman, Matthew Z
Hartzler, Robert G
Archontoulis, Sotirios
Nair, Ajay
Committee Member
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Kochia (Bassia scoparia [L.] A.J. Scott) and waterhemp (Amaranthus tuberculatus [Moq.] J.D. Sauer) are one of the most troublesome weeds in the cropping systems of Great Plains and Midwestern United States, respectively. A widespread occurrence of multiple herbicide-resistant (MHR) B. scoparia and A. tuberculatus populations across the region has seriously limited herbicide options to control these weed species. Therefore, there is an immediate need for ecologically based, multi-tactic strategies to manage these weeds. Laboratory and field experiments were conducted during 2017 to 2019 at the Montana State University Southern Agricultural Research Center, Huntley, MT: 1) to quantify moisture and thermal requirements for germination of B. scoparia and 2) to quantify the effect of winter wheat cover crop and irrigation on B. scoparia emergence patterns across the U.S. Great Plains. Forty-four B. scoparia accessions were collected from northern (Huntley, MT; Powell, WY) and southern (Lingle, WY; Scottsbluff, NE) regions of the Great Plains. Moisture requirements for germination of B. scoparia accessions did not differ between northern and southern regions. It required a water potential of -0.85 MPa and -1.9 MPa to reduce B. scoparia germination by 10 and 90%, respectively. The germination rate was highest at temperatures between 14 and 26 C for all accessions and did not differ among locations. Winter wheat cover crop and irrigation treatments did not influence B. scoparia emergence in the northern region. In the southern region, the winter wheat cover crop did not reduce cumulative emergence of B. scoparia. However, irrigation prompted earlier and faster emergence of B. scoparia. This indicates that in the southern region of the Great Plains, B. scoparia emergence can effectively be stimulated by one to two irrigations during early spring and then controlled with either tillage or non-selective herbicides before planting late-season crops. Field experiments were conducted during 2019 and 2020 at two sites (Iowa State University Curtiss Farm in Ames, IA and Bruner Farm in Boone, IA) to design multi-tactic strategies to manage A. tuberculatus in a corn-soybean rotation. Effect of three herbicide programs (HP) on A. tuberculatus seed inputs was tested in the 2019 corn. The effects of previous year’s seed inputs, cereal rye cover crop, and narrow-row soybean on A. tuberculatus density, biomass, and seed production were tested in the 2020 soybean. A weed seed destructor was used to prevent seed inputs by A. tuberculatus escapes at soybean harvest. In corn, an HP with two sites of action provided only 35% control of A. tuberculatus compared with ≥97% control by an HP with three sites of action. In soybean, no new seed inputs from the previous year’s corn crop reduced A. tuberculatus density and biomass by >30% compared with seed inputs from the previous year’s corn crop. Including a cereal rye cover crop or using a narrow-row soybean reduced A. tuberculatus density by at least 13% and biomass by 50%, compared with a no cover crop or a wide-row soybean. The weed seed destructor physically destroyed 90% of A. tuberculatus seeds at soybean harvest. A combination of all four-control tactics (spanned over two years) reduced A. tuberculatus seed inputs by 95% at the time of soybean harvest. These results indicate that diverse control tactics targeting A. tuberculatus at different life-cycle stages can successfully manage MHR populations.