Economic and management value of weed maps at harvest in semi-arid cropping systems of the US Pacific Northwest

Authors: BARROSO, JUDIT - Oregon State University; SAN MARTIN, CAROLNA - Oregon State University; MCCALLUM, JOHN - Volunteer; Long, Daniel

Submitted to: Precision Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2021
Publication Date: 6/7/2021
Citation: Barroso, J., San Martin, C., McCallum, J.D., Long, D.S. 2021. Economic and management value of weed maps at harvest in semi-arid cropping systems of the US Pacific Northwest. Precision Agriculture. https://doi.org/10.1007/s11119-021-09819-6.
DOI: https://doi.org/10.1007/s11119-021-09819-6

Interpretive Summary: Maps showing the occurrence of late maturing weeds are potentially useful for planning weed control operations after crop harvest. The objective of this four-year study was to apply weed mapping into determining changes in weeds from year to year, evaluate the effectiveness of weed treatments on wheat yield, and assess the usefulness of weed maps in site-specific weed management. In each year, wheat yields were mapped across a dryland wheat field in eastern Oregon by means of a yield monitor-equipped combine harvester. Prior to harvest, weeds had been surveyed from the ground. Tumble mustard, prickly lettuce, Russian thistle, and downy brome were the most predominant weeds. Spatial patterns in these weeds varied with year due to differences in crop and weed control strategy. Tumble mustard and prickly lettuce were equally problematic in spring wheat and winter wheat. In contrast, R. thistle was problematic in spring wheat and downy brome in winter wheat. Weed maps at harvest can provide useful information for evaluating the effectiveness of weed control strategies, detecting herbicide resistance problems, and spraying weeds that regrow after harvest. Combined with yield maps, they are useful for explaining variability in crop yield that is the result of weed pressure.

Technical Abstract: Late maturing weeds are problematic to crop production and need to be controlled before they produce seed. The objective of this study was to spatially characterize the population dynamics of predominant weed species and apply this information into quantifying the effect of treated and untreated weed infestations on wheat (Triticum aestivum L.) yields, and evaluate the potential herbicide savings with post-harvest site-specific treatments. Multi-year grain yield and weed data were aquired at harvest in each of four years (2015-18) within a drylandy production field in eastern Oregon. Abundance of weed species (2015) and percent cover of weed species (2016, 2017, and 2018) were visually estimated on a square grid based on dividing the field into 7-m2 cells. Spatial patterns in the weed community were subject to rapid change and depended on year, crop and weed control strategy. While tumble mustard (Sisymbrium altissimum) was the most predominant and competitive species, the spatial distribution of this weed and that of other species varied each year. Tumble mustard and prickly lettuce (Lactuca serriola) were equally problematic in spring wheat and winter wheat whereas Russian-thistle (Salsola tragus) was problematic in spring wheat and downy brome (Bromus tectorum) in winter wheat. Potential savings from site-specific herbicide application varied from 10 to 95% based on percentage of field infested. Weed maps at harvest are useful for studying weed dynamics, identifying herbicide-resistant weeds, and planning site-specific weed management. Combined with yield maps, maps of late-season weeds may reveal the crop yield variability that is associated with weed competition.