Canola will dry down naturally and can be harvested directly without the application of pre-harvest herbicides. If the field is weedy or canola stems are green, there may be value in applying a pre-harvest herbicide. Pre-harvest herbicides may assist with dry down but will not hasten maturity. Follow all herbicide label specifications.
Canola must be delivered at 10% moisture or below. On a very hot day, canola can drop a couple percent in moisture through the day so it may be possible to start harvest at 11 or 12% seed moisture.
Canola must also be delivered with less than 2% green seed and less than 0.1% heated seed. Crush seeds on white paper to determine the percent that are distinctly green inside and the percent distinctly heated (brown to black inside, e.g. if bin burnt). Seed coats change colour from green to yellow to brown/black. The first seeds to change colour are at the bottom of the main stem. The last seeds to change colour are at the tips of the secondary branches. If an individual seed is half green and half brown, we call that colour changed. Seed colour change advances up the stem at about 10% every 2 to 3 days. Seed colour is a better indicator of maturity than pod or stem colour. It takes approximately 70-80 days from first flower to harvest.
Glyphosate should have good activity on actively growing plants but it may take 1 to 3 weeks before plants are effectively dried down for harvest. Labels typically state application should occur at less than 30% grain moisture.
Eragon LQ is generally faster acting than glyphosate. It works best when applied on warm, sunny days. Control will be best with generous amounts of water; the label states 80 L/ac (21 gal/ac) and you may be disappointed if you use a lower volume. Merge is required with use of Eragon. Tank mixing glyphosate and Eragon can provide sharper weed control. Note that in Western Canada this product is named Heat, if you are reading resources developed by Canola Council of Canada. Apply when 60-75% of seeds have changed colour. It may take about 14 days for plants to dry down.
Reglone is a contact product and therefore requires even higher water volumes for good control. The label indicates 90 L/ac (24 gal/ac) of water should be used. Agral 90 is required with use of Reglone. The product must make contact with green tissue for good control; it could be challenging to hit green tissue low in the canopy. Performance of Reglone will be best if you spray in the evening or on a cloudy day allowing the plant to take up the herbicide, prior to a warm, sunny day. Plant dry down with Reglone tends to be faster and more complete. Avoid shatter losses by harvesting promptly once seeds are at the appropriate moisture content. Apply when 90% or more of seeds have changed colour. It may take 7 to 10 days for plants to dry down.
General tips on spraying pre-harvest herbicides
To get the best bang for your buck, and achieve the best results, producers should make an effort to:
- Drive slow; canola has a big canopy and the spray droplets will not land where you want them to if the sprayer is travelling too fast.
- Do not skimp on water volumes; use the water volume recommended on the product label for good results, especially in canola that has a thick canopy and a lot of plant material to cover.
- Aim at the target; if you have regrowth low in the canopy you may have to lower the boom height (e.g. compared to a fungicide application) to achieve the appropriate spray overlap and spray pattern uniformity.
- Note that even if a herbicide is applied, the plant stems may remain green, especially if they are very thick.
- Go to Sprayers101.com for “Pro Tips for Pre-Harvest and Desiccation Sprays” and various articles on boom height
- OMAFRA Publication 75A: Guide to Weed Control – Canola pre-harvest herbicides (starting on page 243)
- Harvest Management – see pre-harvest aids and combine settings – Canola Council of Canada
- Understanding Distinctly Green and Heated Grading Factors – Canadian Canola Growers Association
- Additional tips in Canola Watch from Canola Council of Canada