A pre-harvest herbicide application is not required, and the crop can dry down naturally. However, winter canola is a high yielding crop with a lot of biomass and herbicides can facilitate direct harvest by drying down weeds and canola plants. Green plant material moving through the combine may cause harvest losses, and ease of harvest is improved when the weed and crop stems are drier. Herbicide application can be helpful if the crop is re-growing or uneven, reducing the risk of pod shatter in mature plants while waiting for immature areas to dry down. Use of a herbicide does not hasten canola maturity. In the thick winter canola canopy, there may still be some green in the stems when a pre-harvest herbicide is used. Harvest the field as soon as the crop is ready, as further dry-down increases risk of shattering loss.
If perennial weed pressure is high and another crop will be planted after the canola, a pre-harvest herbicide application to canola may be the best option for weed control since there is not enough weed top growth for effective control after harvesting the canola.
To achieve the best result with pre-harvest herbicides:
- 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.
- 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.
Herbicide Options and Application Timing
Consult the Crop Protection Hub for herbicide options and application details. The crop stage at the time of application may be different for each herbicide registered for pre-harvest use in canola. Environmental conditions (sunny versus cloudy/dark) play a role in the herbicide activity and the ideal conditions may be different for different products.
When checking the crop to determine if it is ready for a pre-harvest herbicide, look for seeds that have changed from green to brown/black. Any amount of colour change is considered changed, i.e. a mottled green and brown seed is changed colour. Only check seeds on the main stem. If the plant population is low or if plants have a lot of branches (e.g. 10+) check some seeds on branches to ensure they are not very far behind in maturity – they should be firm and not translucent.
The top options for pre-harvest herbicides are:
- Reglone + Agral 90
- Eragon + Merge
- Glyphosate + Eragon + Merge
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. Note that when seed fill is complete, seeds are at about 40% 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 200 L/ha (80 L/ac or 21 gal/ac) and you may be disappointed if you use a lower volume. Merge adjuvant is required with Eragon LQ. Tank mixing glyphosate and Eragon LQ can provide sharper weed control. Apply when 60-75% of seeds have changed colour. It may take up to 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 225 L/ha (90 L/ac or 24 gal/ac) of water should be used. Agral 90 is required with use of Reglone. The product must contact 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. Apply when 90% or more of seeds have changed colour. It may take 7 to 10 days for plants to dry down, but in hot conditions it may change more quickly. 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.