Field Selection
Canola responds best when planted in well-drained soil with a minimum pH of 5.5. Fields with variable drainage and soil pH may have variable stands and yield.
Winter canola requires better drainage than winter wheat and should therefore be grown on well-drained soils. Winter canola generally has good tolerance to freezing temperatures but reasons for poor winter survival include root heaving, root rot and freeze injury from ice accumulation often occurring where canola is planted into heavy or poorly drained soils. Do not grow winter canola in fields where winter wheat survival is generally poor.
Herbicide Carryover
Look back 2 years in the herbicide application history for a field before planting canola. Canola is sensitive to several residual herbicides and there is a 22 to 26 month restriction to canola for products containing atrazine, imazethapyr, metribuzin and flumetsulam. Numerous other herbicides have 4 to 11 month restrictions to canola. Herbicide carryover is higher on soils with low organic matter, soils with high or low pH, and under very dry conditions because of the reduced level of herbicide breakdown. Consult herbicide labels and OMAFA Crop Protection Hub for specific product precautions for herbicide carryover.
Crop Rotation
Crop rotation is an excellent way to reduce build-up of diseases and insects. Rotations of 3–4 years between canola are recommended. Long rotations with non-host crops for clubroot, sclerotinia (white mould), blackleg and swede midge will help reduce buildup of these pests in canola. To mitigate buildup of clubroot spores it is also necessary to control volunteer canola and weed species from the Brassica family throughout the rotation, including mustard, shepherd’s-purse, field pepperweed, stinkweed, yellow rocket and radish.
In Ontario, winter canola is commonly seeded following winter wheat harvest or may be seeded after an early soybean harvest in southern regions. Most other field crops are harvested too late to follow with winter canola. Fresh vegetable or dry pulse crops may be harvested early enough in some regions to seed winter canola at an ideal time but there are often herbicides used in these crops that restrict seeding to canola (e.g. Group 2 herbicides with a 22 month restriction to canola).
Occasionally in some regions, it may be possible to plant soybeans after winter canola harvest. The success of “double crop” soybeans depends on planting date and having timely rain for soybean germination and emergence. Fall seeded cereals or alfalfa can also be planted after winter canola harvest.
Corn should not directly follow winter canola in the rotation because of the potential for phosphorous deficiency in the corn. After winter canola harvest, seed a crop that hosts beneficial arbuscular mycorrhizae fungi (AMF) present in the soil; oats are an excellent choice, but soybeans and many cover crop species are also options. Corn roots establish a strong relationship AMF which aids in phosphorus uptake. AMF colonize on roots of corn seedlings and the underground fungi network acts as an extension of the corn seedling roots, allowing for uptake of phosphorous from a greater volume of soil. Canola is not a host of AMF, so AMF colonization on roots of corn seedlings is diminished when corn follows canola resulting in increased incidence of phosphorus deficiency. Phosphorous deficiency may cause delayed corn maturity and/or reduced yield. Phosphorous deficiency in corn following canola is expected to be completely mitigated by growing oats or another AMF host crop after canola harvest and may also be mitigated by high soil phosphorous levels and seed-placed or side-banded phosphorous fertilizers.
After winter canola harvest there will likely be a high number of volunteer canola plants and they will not die over winter. Control any volunteer canola in the fall or early in the spring before they grow large and difficult to manage.
Do not locate winter canola within 5 km of where rutabagas are grown. Both crops are hosts for turnip mosaic virus. Serious crop losses have occurred in rutabagas from this disease.