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The effects of canola cultivar, seeding rates and herbicide use on weeds and canola
Thesis (MScAgric)--Stellenbosch University, 2025.
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867613883418542080 |
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| access_status_str | Open Access |
| author | Riet, Robin Laiken |
| author2 | Viljoen, Charne |
| author_browse | Riet, Robin Laiken Viljoen, Charne |
| author_facet | Viljoen, Charne Riet, Robin Laiken |
| author_sort | Riet, Robin Laiken |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MScAgric)--Stellenbosch University, 2025. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/133572 |
| institution | Stellenbosch University (South Africa) |
| last_indexed | 2026-06-10T12:43:13.574Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/133572 The effects of canola cultivar, seeding rates and herbicide use on weeds and canola Riet, Robin Laiken Viljoen, Charne Strauss, Johann Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy. Canola -- Breeding -- South Africa -- Western Cape Herbicide-resistant crops Canola -- Weeds -- Control -- Management Canola -- Growth Seedlings -- Evaluation UCTD Thesis (MScAgric)--Stellenbosch University, 2025. Riet, R. L. 2025. The effects of canola cultivar, seeding rates and herbicide use on weeds and canola. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/5494390a-f4ca-4b48-99b2-57875a9fc807 ENGLISH ABSTRACT: The inclusion of canola (Brassica napus) in Conservation Agriculture (CA) systems aids farmers in increasing the production of wheat and barley by breaking disease cycles and aiding in weed control. Herbicide-tolerant canola cultivars have improved weed management by using selective herbicide application. Due to the reduction of tillage as a tactic to increase soil integrity and health, high dependence on herbicides increases the risk of herbicide-resistant weeds through continuous herbicide application. This study investigated the weed suppression ability of two herbicide-tolerant canola cultivars at various seeding rates in the presence and absence of herbicides. The trials were conducted in the Swartland at the Langgewens Research Farm in the Western Cape over the 2023 and 2024 seasons. The trial consisted of three factors: cultivar, seeding rate and herbicide use. Two different Triazine-tolerant (TT) varieties and two Imidazolinone-tolerant (Clearfield) varieties used across seasons. A subplot factor of herbicide use where herbicide was either applied or received no herbicide application. A split-plot factor of four seeding rates, 1 kg ha-1, 2 kg ha-1, 3 kg ha-1 and 4 kg ha-1 were randomly allocated. Sixteen unique plot combinations were replicated four times, resulting in a total of 64 plots of each site plant. As a growth parameter, canola and weed densities and biomass were collected at 30, 60, and 90 Days after emergence (DAE) and pre-harvest. At the end of each season, the canola yield was collected and quality examined. A botanical composition analysed by Non-metric Multidimensional Scaling (NMDS) was done. In 2023, significant interactions between cultivars and herbicides occurred (p≤0.05). Clearfield canola was able to produce more biomass, yield and heavier seeds than TT, even when herbicide use was absent. There was a positive relationship between seeding rates and biomass and seeding rates and yield. Canola plant densities at 30 and 60 DAE, biomass at 90 DAE and yield increased as seeding rates increased. The interaction between cultivar and herbicide use also impacted the weed biomass and densities. Clearfield was able to suppress weed better than TT when herbicide was absent. At pre-harvest, a third-order interaction between cultivar, herbicide use, and seeding rate occurred. It was found that with higher seeding rates, TT could not suppress weeds as well as Clearfield. When herbicide was absent, Clearfield canola was able to decrease weed biomass as the seeding rates increased. However, when herbicide was present, weed biomass remained lower than that of plots that had herbicide absent. In 2024, high rainfall hindered the productivity of Clearfield through secondary dormancy effects caused by the environmental effect. Significant effects of cultivar factor, seeding rate factor and herbicide use factor occurred without any significant interaction. Due to climatic conditions, secondary dormancy likely occurred, and canola growth was severely impacted. Triazine-tolerant canola produced higher canola plant densities, biomass, and yield than Clearfield, which likely explained the variation in the two cultivars' performance. Clearfield produced higher oil content and seed weight than TT. Canola densities, biomass and yield increased as seeding rates increased. The effects of the use of herbicide present led to higher canola densities and yield compared to when herbicide was absent. Weed control was poorer in 2024 due to higher weed densities that occurred in the specific sites selected and the lack of primary grass-selective herbicide application. Cultivar use had little effect on the weed densities and biomass; seeding rates did not affect the weed growth. Weed densities and biomass remained high at all four seeding rates. Only herbicide use affected weed control. Lower weed densities and biomass occurred when herbicide was present. The NMDS found that species differentiated more through cultivar selection than herbicide use and seeding rates. Unique species groups occurred in different cultivar clusters. Cultivar selection has the potential to be used as a tool to mitigate high dependence on herbicide use. Higher seeding rates can improve the production and profitability of canola. Furthermore, the study highlighted that completely removing herbicide use is an unviable choice. In addition, the interaction between cultivar and herbicide use in the 2023 season indicated how integrated weed control options can mitigate weed herbicide resistance. AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar. Masters 2025-08-18T10:21:37Z 2025-08-18T10:21:37Z 2025-03 Thesis https://scholar.sun.ac.za/handle/10019.1/133572 Stellenbosch University xi, 70 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Canola -- Breeding -- South Africa -- Western Cape Herbicide-resistant crops Canola -- Weeds -- Control -- Management Canola -- Growth Seedlings -- Evaluation UCTD Riet, Robin Laiken The effects of canola cultivar, seeding rates and herbicide use on weeds and canola |
| title | The effects of canola cultivar, seeding rates and herbicide use on weeds and canola |
| title_full | The effects of canola cultivar, seeding rates and herbicide use on weeds and canola |
| title_fullStr | The effects of canola cultivar, seeding rates and herbicide use on weeds and canola |
| title_full_unstemmed | The effects of canola cultivar, seeding rates and herbicide use on weeds and canola |
| title_short | The effects of canola cultivar, seeding rates and herbicide use on weeds and canola |
| title_sort | effects of canola cultivar seeding rates and herbicide use on weeds and canola |
| topic | Canola -- Breeding -- South Africa -- Western Cape Herbicide-resistant crops Canola -- Weeds -- Control -- Management Canola -- Growth Seedlings -- Evaluation UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/133572 |
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