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. Spring canola is commonly grown on many different soil types in Ontario, including loams, clays and muck soils.
Spring canola can suffer during dry periods in soils that have low moisture holding capacity. Spring cereals are more resilient to dry growing conditions than spring canola.
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 and swede midge populations 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. However, any canola fields nearby may contribute to local insect pest populations.
Corn should not follow spring canola in the rotation because of the potential for phosphorous deficiency in the corn. Corn roots establish a strong relationship with beneficial soil fungi called arbuscular mycorrhizae fungi (AMF) which aids in phosphorus uptake. AMF colonize on roots of corn seedlings and the underground fungi network act 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 may be mitigated by high soil phosphorous levels and seed-placed or side-banded phosphorous fertilizers.
Canola is versatile in a crop rotation. Canola harvest dates allow for timely winter wheat planting. Many producers report their best winter wheat yields following canola in the rotation. Following canola harvest there will likely be a high number of volunteer canola plants. While most will die over the winter, control any volunteer canola present in the spring early-on, before they grow large and difficult to manage.