3 Symptoms of Heat Stress of Canola


30 degree C days are great for the lake life, but not so great for crop yields. Many of the crops grown across Western Canada are known as “cool season” crops, even though this may seem misleading as 25 degrees C may not seem all that “cool.”  Most western Canadian crops really do prefer temperatures that stay below that 25 degree C mark, and many crops are negatively affected by our heat waves. The crop that almost always ends up with the most attention is canola. Here are three things you will see this summer in your canola crop that is a sign heat has started to take its toll:

1. Bud blast/aborted flowers. The first thing heat is known to do is cause flower abortion or “bud blast” as it is often referred to. This is when the temperature and humidity have caused flower(s) to go un-pollinated and therefore cause blanks in the stem. Temperatures that rise above 25 degrees C hinder many physiological processes in canola causing this, including decreased movement/uptake of nutrients such as boron that are key for pollination and seed/pod development. To top this off, certain plant hormones that are important for flower formation and seed set are not stimulated efficiently. Periods of high temperatures can cause a “hangover” effect, taking a few days for a plant to get back to normal functioning even once temperatures have cooled off.

2. Sunscald/purple pods. The next thing that seems to be a hot topic every year is the purpling of canola pods, or sun scald. I often hear this misdiagnosed as a nutrient deficiency. If you are seeing a purpling of the pods during ripening, simply look at the under part of the pods that is not exposed to the sun and you will see a regular green/yellow colour that you would expect. The cause is generally a response to stress from intense heat/sunlight and is a build-up of pigments known as anthocyanins. The one thing you will notice is that some varieties tend to show more of it than others, much like some individuals get sun burnt more than others.

3. Leaf droop/wilting. What many see even before flowering or pod development is leaves drooping or wilting occurring during periods of high temperatures. This is a sign that your crop has went into what I call a “defensive” mode – decreasing photosynthesis and any translocation within the plant to conserve energy and decreasing turgor pressure and closing stomata to conserve moisture. Typically, this wilting disappears once there is a temperature drop.

The yield effects these factors can have on crop yield can be anywhere from virtually nothing to significant depending on a few factors including how hot the temperatures got and the length of time they stayed up that high. Generally speaking there isn’t anything you can do aside from ensuring a healthy crop with a good nutrient package or having proper irrigation management practices if that is an option. Some farmers do choose to move seeding dates to try and avoid the hottest part of the summer, but weather doesn’t always follow the average, as we well know.

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