Heat Stress on Canola Crops

Jonathan Barratt

July 5, 2022

Heat stress on canola crops is a serious risk for Australian farmers.

Canola is an important crop for Australian Farmers and on average growers produce 3 million metric tons annually. Domestic growers supply more than 2.5–3 mmt, or between 15–20 percent of the world’s trade reaching out to Europe, China, Pakistan, Japan, and other international markets. At today’s price of $950/t+ this represents $2.85 billion worth of income. It is a serious crop. Securing this return for farmers comes down to on-farm management skills and the weather. The weather’s input is critical and to hedge the weather will help secure the return.

Adverse weather conditions, such as drought, excess rain at harvest, high and low temperatures can all influence yield. Heat stress is one adverse weather event that can cause significant yield loss. AAFC research scientist Malcolm Morrison in Canada found that yield loss for canola plants would start to occur when temperatures during flowering exceeded 29.5 C. (https://www.youtube.com/watch?v=nvYGMJ7qVfQ). The more heat stress units, the greater the yield loss in fact he found that 4% of yield was lost per heat stress unit. Put simply, if during this risk period you had two days where the maximum temperatures were 32° the farmer’s yield lost would be 20%. (32° – 29.5° = 2.5; 2.5 x 2 days = 5units)

Shows the negative effect of heat stress on canola crop yield
Effect of the accumulation of daily heat stress on yield of canola (Morrison and Stewart 2002.

More specifically, heat stress 2 weeks after the first flower and then 2 weeks after flowering has ceased are critical for yield. Temperatures over 25°C, 27°C and 30°C, during this 45-day risk period in Australia is detrimental to the sterility of the plant and thus yield. Given the high price of canola and the high input prices, it is crucial that growers look to protect yield where they can. (Angadi et al. 2000), Gan et al. (2004)

CelsiusPro has developed a parametric weather certificate that is triggered when the daily maximum temperatures pass 25°C, 27°C, or 30°C. The hotter it gets per day over the risk period the more the cover pays.


Farm location: Wagga Wagga (Lat: -35.05 Long: 147.15)

Crop: Canola

Production Cost: $450/ha over 1000ha sown = $450,000

Yield to Breakeven: 0.96t/ha

Expected yield: 1.33t/ha

Risk period: 1st August through 15th Sept (45 days)

Rational: Heat stress starting at 50% of the flowering time through to mid plodding

At the end of the risk period, one of the following three scenarios will have occurred

Scenario One

The maximum temperature was not greater than 27°, and the cover would expire with no payout, yet the farmers received the expected yield.

Scenario Two

The maximum temperature on one day was 29°which represents two heat stress units with the potential yield loss of 8% or 0.106t/ha. The payout would be $100,000 which is approximately the same as the monetary value of the yield loss based on historical prices of $750/t.

Scenario Three

The maximum temperatures were recorded at 28°, 29°, and 30°. The number of heat stress units totalled 6 so the potential yield loss was 24% or 0.32t/ha. The payout would be $300,000 which is approximately the same as the monetary value of the yield loss based on historical prices of $750/t.

All parameters can be changed to suit the farmer expectations and perceived risks. Premiums range from 5% – 10% of the sum insured. Temperatures are measured via BOM grid or Weather Station.

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