Canola: Timing of Herbicide Application in Relation to Harvest

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Canola Agriculture Crop Protection

Canola is one of the most important oilseed crops, valued for its oil content and diverse applications in food production, biodiesel, and more.

Achieving optimal yield and oil quality requires careful management, particularly concerning the timing of herbicide applications and harvest.

Herbicide residue and its impact on seed viability, germination, and oil content

The timing of herbicide application is crucial in determining its impact on canola seed quality. Herbicides applied too close to harvest can leave residues on the seeds, potentially affecting their viability, germination rate and oil content.

  • Seed Viability: While systemic herbicides like glyphosate are absorbed into the plant, the notion that they compromise seed viability is contested. Herbicides with glyphosate are safe when used according to label recommendations.
  • Germination: Herbicide residues can interfere with the enzymes responsible for breaking down seed reserves, which are necessary for germination. Seeds exposed to high levels of herbicide residue may show delayed or poor germination, leading to uneven stands and reduced crop performance.
  • Oil Content: The timing of herbicide application can also affect the oil content of canola seeds. Residual herbicides can interfere with the plant’s metabolic processes, potentially reducing the accumulation of oils in the seed. For canola, where oil content is a primary quality parameter, ensuring that herbicide applications do not coincide with critical stages of oil formation is vital.

Herbicide carryover and its effects on subsequent crops

Herbicide carryover is a significant concern in crop production, especially when rotating to crops that are sensitive to the herbicides used in the previous season.

Herbicides that persist in the soil can carry over to the next growing season, potentially affecting the germination and growth of subsequent crops. Crops such as legumes and certain vegetables are particularly sensitive to herbicide residues. Carryover can result in poor crop establishment, reduced yield, and even total crop failure in severe cases.

To mitigate the risks of herbicide carryover, several strategies can be employed:

  • Crop Rotation: Selecting crop species that are less sensitive to the residual herbicide can help reduce the risk of damage.
  • Soil Management: Practices such as deep tillage can help to dilute or bury herbicide residues, reducing their impact on the subsequent crop.
  • Cover Cropping: Planting cover crops between main crops can help to degrade herbicide residues and improve soil health.
  • Herbicide Selection: Choose herbicides with shorter re-cropping intervals and that work well with crop rotation.

When are canola fields harvested?                                   

Canola fields are typically harvested when 60-70% of the seeds in the pods on the main stem have turned from green to brown or black. This stage usually occurs about 35-45 days after flowering, depending on the growing conditions and variety. Harvesting at this optimal time ensures maximum yield and oil content, as it allows seeds to mature fully and reduces the risk of shattering. Straight cutting Canola has become more prevalent in western Canada in recent years, as it saves time and costs for growers.

Herbicide resistance management in canola systems

Herbicide resistance is an ever-growing concern in modern agriculture. Managing herbicide resistance within canola systems is essential to maintain effective weed control and prolong the efficacy of available herbicides.

Overreliance on a single herbicide mode of action can lead to the development of resistant weed populations. Once resistance develops, controlling these weeds becomes significantly more difficult and costly.

Strategies for resistance management:

  • Crop Rotation: Regularly rotating crops with different herbicide requirements can help break the cycle of resistance development. Different crops may require different herbicide modes of action, reducing the selection pressure on weed populations. Glufosinate tolerant canola is one way to add another effective mode of action (Group 10) to the herbicide program.
  • Tank Mixing: Using tank mixes that combine multiple herbicide modes of action can provide more comprehensive weed control and reduce the likelihood of resistance developing. For instance, combining a canola herbicide with a different mode of action can help target resistant weed species more effectively.
  • Alternative Herbicides: Incorporating alternative herbicides or cultural practices into your weed management strategy can also help manage resistance. Non-chemical methods such as mechanical weed control or cover cropping can reduce reliance on herbicides and help manage resistant populations.
  • Monitoring and Diagnostic Tools: Regularly monitoring weed populations for signs of resistance is essential. Diagnostic tools can be used to confirm resistance and identify the specific herbicide mode of action to which the weeds are resistant.

Timing is a critical factor in canola herbicide application, particularly in relation to harvest. Properly timed herbicide applications can minimize the negative impacts on seed viability, germination and oil content, while also ensuring an efficient harvest. Understanding the persistence of herbicides and their potential for carryover is essential for protecting subsequent crops. Additionally, implementing effective herbicide resistance management strategies is crucial for sustaining the long-term efficacy of weed control measures.

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