Canola Weed Management

Effective Canola Weed Management: Strategies for Higher Yields and Cleaner Fields

Canola can successfully suppress weeds after the rosette formation stage due to the good (extensive) soil coverage that the leaves of the plant offer. This can be further facilitated with closer planting distances. However, during emergence, canola (especially winter-type) is very sensitive to weeds that can easily outcompete the crop and “drown” it. For this reason, the farmer should offer his/her crop a clean start (weed-free seedbed) by performing tillage (1-3 applications before sowing), using appropriate herbicides, or both. Additionally, it is best to choose varieties with high, fast, and uniform germination rates and avoid planting the seed too deep (it can delay emergence). To improve the result and manage more effectively (and long-term) the weed population, it would be beneficial to adopt an appropriate crop rotation.

Some of the most common canola weeds are:

wild oat (Avena spp.)
Canada thistle (Cirsium arvense)
henbit (Lamium amplexicaule)
common chickweed (Stellaria media)
Bromus species
feral rye (Secale cereale)
jointed goatgrass (Aegilops cylindrica)
Italian ryegrass (Lolium multiflorum)
volunteer wheat (Triticum aestivum)
bushy wallflower (Erysimum repandum),
mustard species
flixweed (Descurainia sophia)
field pennycress (Thlaspi arvense)
shepherd's-purse (Capsella bursapastoris)

Except for the pre-emergence and selective herbicides, the farmer can use Clearfield (imidazolinone) resistant canola hybrids that allow post-emergence applications with herbicides (against the grass and broadleaf weeds).

When herbicides are applied, it is essential to apply them 4-6 weeks (8 weeks at most) after sowing to control the weeds successfully. Waiting too long will reduce weed control efficiency and put the final yield at risk. More specifically, research had shown a yield difference of up to 400 lb/acre (448 kg/ha) when the chemical weed control was applied in the 3-leaf stage of canola instead of the 6-leaf stage (1). However, each product has its own requirements regarding the best application time (crop and weed growth stages). To determine if there will be a need for a second application, the farmer should check his/her field in early spring and evaluate the number of weeds (2, 3).

The farmer should be cautious when selecting a pesticide for his/her canola field and always consult a licensed agronomist. While most pesticides appropriate for rapeseed can be used in canola, the opposite is not true. To be sure, it is best to advise a representative of the company manufacturing the product. Finally, canola is very sensitive to some widely used broadleaf herbicides (like sulfonylurea, ALS-inhibitor herbicides, etc.) used in crops like corn and wheat. If you are planning to sow canola in a field, avoid using such products in the previous crop, especially if they have an extended residual life (4). Additionally, be careful when such crops are cultivated near your canola field simultaneously because even the chemical drift of such products (used by your neighbors) can cause toxicity problems to your canola plants.

References

Further reading