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ARS Home » Pacific West Area » Pendleton, Oregon » Columbia Plateau Conservation Research Center » Research » Publications at this Location » Publication #356853
Title: Spring crops in three year rotations reduce weed pressure in winter wheat

Author
item SAN MARTIN, CAROLINA - Oregon State University
item Long, Daniel
item GOURLIE, JENNIFER - Oregon State University
item BARROSO, JUDIT - Oregon State University

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2018
Publication Date: 3/1/2019
Citation: San Martin, C., Long, D.S., Gourlie, J., Barroso, J. 2019. Spring crops in three year rotations reduce weed pressure in winter wheat. Field Crops Research. 233:12-20. https://doi.org/10.1016/j.fcr.2018.12.017.
DOI: https://doi.org/10.1016/j.fcr.2018.12.017

Interpretive Summary: Downy brome is a grass-weed that is difficult to control in low rainfall areas of the inland Pacific Northwest where winter wheat is grown in rotation with fallow. A field study was conducted to determine if three year rotations of fallow / winter wheat / spring barley or fallow / winter wheat / spring carinata can improve management of this weed. Spring carinata is an oilseed crop with branching habit that can crowd out weeds. Light-tillage and herbicides are normally used to control weeds during the fallow period. Weed density and cover of weeds and winter wheat yields were measured in each rotation and compared with a normal two year rotation of fallow / winter wheat. After two crop rotation cycles, grass cover and density were higher in fallow / winter wheat than both three year rotations. Winter wheat plots of fallow / winter wheat had more downy brome than fallow / winter wheat / spring barley or fallow / winter wheat / spring carinata indicating a greater ability of the three year rotations to control this weed. In 2018, the 3-yr rotation with spring barley had greater winter wheat yield than fallow / winter wheat even though weeds were more competitive in fallow / winter wheat / spring barley. Results show that introducing a spring crop can help control downy brome in winter wheat.

Technical Abstract: Downy brome (Bromus tectorum L.) is a problematic weed for the conventional fallow / winter wheat (F / WW) production system in low precipitation (<340 mm yr-1) region of the Pacific Northwest. A 4-yr field experiment was conducted to determine if incorporating spring barley (SB, Hordeum vulgare L.) or spring oilseed (SO, Brassica carinata A. Braun) into 3-yr crop rotations with WW would benefit weed management. The experimental design was a randomized complete block with four replications where each phase was present every year for the following rotations: 1) F / WW, 2) F / WW / SB, and 3) F / WW / SO. Reduced tillage, consisting of a single undercutting operation with a wide-blade sweep, and herbicides were used to control weeds during the fallow period. Weed density and cover per species and WW yield were evaluated in each rotation. Grass cover and density after one and two complete cropping cycles were significantly higher in F / WW than in F / WW / SB and F / WW / SO. Reduction in density and cover of total weeds was found after two cycles. However, differences in community biodiversity were only found between F / WW, and F / WW / SB or F / WW / SO in 2017. Winter wheat plots of F / WW had more downy brome than F / WW / SB or F / WW / SO indicating the greater capacity of the latter to control this weed. In 2018, the 3-yr rotation with SB had greater WW grain yield compared with F / WW when weeds were not present though weeds were more competitive in F / WW / SB. Results show that introducing a spring crop can control weeds, especially downy brome that competes with WW in the Pacific Northwest.