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The Potential for Targeting Alternate Life Cycle Stages of Western Canadian Weeds
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- Author / Creator
- Tidemann, Breanne D
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Over-reliance on herbicides to manage weeds in agricultural crops has selected for herbicide resistant weeds globally. Harvest weed seed control (HWSC), an Australian developed and optimized paradigm of weed control, targets newly shed seed to reduce seed bank inputs. For species to be managed by HWSC they must retain seeds until crop harvest at a canopy height where they will be collected by the harvester. Seed retention characteristics of wild oat, cleavers and volunteer canola were determined over six site-years in Alberta and Saskatchewan to determine their suitability for HWSC. Overall ranking of HWSC management potential was canola > cleavers > wild oat, with wild oat a concern due to economic impact and resistance levels. A periodic demographic matrix model was developed to determine the potential impact of HWSC on population growth rates of wild oat and to identify other life cycle stages as potential control opportunities. The model emphasized that early seed shatter of wild oat limits potential of HWSC technologies on population management. Across tested treatments, 80% wild oat seed control was required before seed bank additions occurred for HWSC to reduce or stabilize populations. Potential life cycle stages for management included the over-winter seed bank, plant fecundity (seed production), and the growing season seed bank. The seed bank was a critical component of the wild oat life cycle, particularly when survival of newly shed seeds was limited. Stationary threshing was used to evaluate the Harrington Seed Destructor (HSD), a HWSC technology, for the effects of weed species, weed seed size, seed number, chaff type and chaff volume on weed seed devitalization. This study determined that the HSD has > 97% efficacy on five problematic Canadian weed species, and that seed size was not likely to limit management with > 98% control at all canola seed sizes tested. Increases in weed seed number or chaff volume significantly affected weed seed devitalization but the small differences were unlikely to be biologically relevant in the field. Volunteer canola devitalization was significantly decreased in canola chaff when compared to barley or pea chaff. This could be due to protective structures such as pods in the chaff or due to an underlying presence of volunteer canola in the chaff. Over all tested conditions and species, devitalization of seeds with the HSD was high, indicating that population control will be primarily limited by the ability to get seeds into the HSD and not HSD efficacy. Germination stimulant compounds could provide an additional tool to manage seeds shed prior to harvest, or that are produced below harvest cutting height. Compounds would either induce germination prior to environment-induced mortality, or have herbicidal effects. Fluridone, which has been previously reported to have both germination stimulant and herbicidal effects, was tested in western Canada for stimulant properties in field studies with fall applications, as well as rotational crop tolerance. No significant stimulation was observed, however there were indications of potential stimulant activity. Rotational crop tolerance of canola was poor, including severe injury and death. In this study the risks of fall fluridone applications outweighed the potential benefits of weed germination stimulation. Overall, the potential of HWSC in western Canada was highlighted with limitations for Canadian producers also identified. Wild oats have poor potential to be managed by HWSC, and the seed bank and fecundity were identified as future management targets. Additionally, fluridone applications to manage seeds not available for HWSC led to rotational crop damage and limited germination stimulant efficacy. None of the tested methods provided a complete solution to herbicide resistant or susceptible weeds but may be useful additions to integrated weed management systems in western Canadian crops.
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- Graduation date
- Fall 2017
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.