By Harry Brook
While conducting crop surveys lately, I've noticed a few thieves lurking in the fields in the area. These are thieves, robbing crop yield yet not obvious to the casual observer. The results of their work usually show up when you get less yield than the straw or crop volume would indicate.
In canola, we’ve all heard about clubroot and sclerotinia and they tend to be on the mind. However, an old enemy is making a comeback. That culprit is blackleg. It was a serious problem in the early 1990s until we developed resistant genes for the disease. Now, it is creeping back into the field, not necessarily killing a lot of plants but there is a lot of it present in most of our canola fields and it is stealing yield.
Blackleg, for those that might have forgotten, is a disease that starts early in the plant. When using fungicide to protect the crop, it must be applied at the 2- to 6-leaf stage to effectively protect the crop. This is much earlier than spraying for sclerotinia. We’ve got so used to having good genetic resistance we forget how severe the yield loss can be.
Blackleg spores germinate in the spring, on canola residue that was grown last year. These spores don’t travel too far but they begin the infection process on the leaves. The real problem comes in the second year after canola. That is when a different type of spore is produced which can travel 100s of metres and infect large swathes of the field. The real problem is that many producers are on a canola cereal rotation so that the canola is seeded when the travelling spores are produced, perfect for infection spread.
At harvest this year, take some time to pull a few canola stems and cut them off at the soil surface. Any black inside the stem is a sign that blackleg was present. The fungus plugs up the xylem, which transports water and nutrients up the plant to help fill the seed. If those tubes are blocked, either fully or partially, they’ll prevent adequate filling of the seed and disappointing yields are the result.
Cereal crops have their own thieves stealing yield. It is often seen as root disease early in the plants’ life or leaf diseases as the cereals head out. In cereals the crucial thing to remember is that the majority of the seed filling is done by the top two or three leaves. Stopping disease from spreading on these leaves is vital to protect the plants’ ability to properly fill the head. Remember, a fungicide is not usually a cure, it just prevents further damage from being done.
When using a fungicide, they do not translocate, as seen in herbicides, but need to be applied in high water volumes to maximize coverage. If you go too light on the fungicide, your whole plant is not protected.
Keep an eye on those crops and do a little investigating to prevent a disappointing result from filling your bins. Keep the thieves at bay. Be vigilant and learn from this year’s lessons.