Meghan Moran, OMAFRA’s Canola and Edible Bean Specialist, recently spoke at Co-op Régionale’s annual Grower’s Day in Temiskaming. Her presentation was about canola management and she spoke about some fertility and deficiency issues seen this year, and then some best practices for fast emergence of canola in the spring.
A common issue with canola is phosphorus deficiency because canola has a very high phosphorus requirement. Phosphorus deficiency results in small, scrawny looking plants, sometimes with discolouration or purpling, though many things could cause that. Canola requires about 75 pounds of phosphate per acre over the course of the season, and then at harvest 46 pounds of phosphate is removed with the grain. An issue with maintaining phosphate levels is that it can’t all be added to the field during planting, or else the seedlings could suffer from toxicity due to the amount. A seed drill is better than a broadcast seeder for allowing the seedlings to have access to phosphorus, but again, you want to avoid putting too much phosphorus directly on the seeds. Somewhere between 20 or 25 pounds of phosphate per acre, if planted with the seeds, is what Moran suggested. She also suggested seeding a section without the extra phosphate as a control group to gauge its effectiveness.
Boron deficiency can also be an issue with canola, and results in thick, rough-skinned leaves that curl. This is a fairly uncommon problem, and one that can only reliably be diagnosed by a plant tissue test. Boron deficiency is most commonly found in sandier soil where there is less organic matter in the ground, as boron comes from that organic matter. Boron deficiency can be remedied by, you guessed it, applying boron. Since it’s a small micronutrient, only about 1.5 to 1.7 pounds per acre of soil-applied boron is necessary to maintain good levels. With canola, less than a pound an acre of boron is removed during harvest. Foliar boron is often applied during flowering, though its efficacy is in question, and may depend on soil type or other factors. For foliar boron, about half a pound to the acre is commonly applied.
Sulphur deficiency is another problem that’s fairly rare because of the widespread awareness that sulphur is necessary for canola. Sulphur deficiency results in purpling and cupped leaves, and small and pale flower petals later in the year after sulphur applied during planting has been used up. In a test conducted during 2019 it was found that applications of 20 pounds of sulphur and 100 or 150 pounds of nitrogen per acre resulted in the highest yielding canola. Adding more sulphur or nitrogen didn’t seem to improve yield much above the yield of the plots with 20 pounds of sulphur and 100 or 150 pounds of nitrogen. One issue that was experienced with the plots that had no sulphur applied was that since they took longer to mature, they were more susceptible to damage from flea beetle insects. This holds true for most fields with fertility issues: since growth is generally delayed the plants suffer more damage to pests like swede midge as well.
Some swede midge research was also conducted this year to better understand the lifespan of the insect. Swede midge emerges in either two or three waves depending on conditions. In early June the first generation emerges out of the ground and lays their eggs during their two day lifespan. It takes the eggs about a week to hatch depending on the air temperature. Below 5 degrees the eggs won’t hatch, but above 6 degrees they will, and the warmer the air the faster the eggs will hatch. At 10 degrees the eggs will hatch after 8 days. When the eggs do hatch that’s when the larvae eat canola and plant damage occurs. Ideally the canola has 5 or 6 weeks of growth already before the larvae emerge, which would mean a planting date of about the first of may, though that isn’t always a realistic goal. Another technique to avoid swede midge is to plant canola in secluded fields, away from other fields that may have swede midge as a bit of a quarantine.
There is a beneficial wasp that kills swede midge. The wasp, Synopeas myles, is very small and lays its eggs on swede midge larvae, which kills it. A recent test was conducted to see what the effects of swede midge insecticides were on the wasp, and it was found that one insecticide, Matador, kills the wasps, while another, Coragen, doesn’t seem to have an effect on them. Switching to an insecticide that doesn’t affect the beneficial insects might be a good idea.
Moran summed up with some top tips to think about when going forward with canola. First, fertility, time of planting, soil temperature at planting, and seeding depth are some of the things beside pesticides that can help with pest management. They will also help determine uniform emergence and growth across the field.
For fertility, phosphorus is important, and to that end regular soil sampling is also important to figure out what other nutrients ma be needed. For soil temperature and weather, canola seedlings have some frost resistance but ideally planting should be done after frost. Frost will, if not kill the seedlings, then certainly delay their growth and make them more susceptible to pests. Seeding into cold soils is also hard on the seeds. The seeds may die or their emergence may be delayed in cold soils. Moran pointed out that the longer the seed is in the ground without emerging, the less efficacy any treatment planted with the seed will have because it has had more time to get washed off the seed or otherwise get wasted.
Seeding depth for canola is fairly shallow, between one and two inches depending on conditions and soil warmth. A 3 inch seeding will result in a lot of seedling death, as canola just doesn’t have the energy reserves to make it that far. Recent testing found that for canola planted at precisely an inch deep, the emergence was 100%, but for canola planted at a depth of 2 inches the emergence fell to 50%. Moran suggests aiming for an inch, but erring on the shallower side. Again, uniformity of planting helps result in uniformity of growth and helps the canola all reach maturity at once.
Moran concluded with a little bit of information on clubroot. Clubroot has been found in the Temiskaming region, and elsewhere across Ontario. Clubroot is a pattern of abnormal growth in the roots of canola that makes them swell up and can ultimately kill the plant. Clubroot is caused by infection from a spore in the soil. When a plant has been infected by clubroot it can then release some one billion new clubroot spores into the ground, and it only takes about 10 000 spores in a gram of soil to infect a plant.
There are clubroot resistant varieties of canola available, and Moran recommends using those resistant varieties even if a farm doesn’t have clubroot, just as a precaution. Even so, these resistant varieties are not a cure-all, clubroot can still affect these plants. Something to be aware of is that planting the same clubroot resistant variety of canola over and over will put a selection pressure on the clubroot spores, encouraging those that are not affected by the resistance, and in as little as two years the clubroot resistant variety won’t be resistant to the clubroot population in the field. It works similarly to how antibiotic resistance builds up.
The main way to counter clubroot is to maintain a three or four year crop rotation. In a non-canola field, up to 90% of the clubroot spores may die off. The problem, as Moran points out, is that 10% of four billion is still a lot of spores. Long rotations are advantageous for keeping the spore populations under control. The spores can also stick to dirt on equipment and be carried into new fields that they can then infect, even if it’s not a canola field. To combat this, equipment should be washed off before moving from field to field to limit spore movement.