A long season of drought and heat stress has affected canola growth and ripening. Producers reporting seed sprouted in pods (precocious germination) are looking for reasons why this occurred and how to manage harvest.

Diagnosis

Pre-harvest scouting is a good time to check colour change of pods and seeds. Sprouted seeds found at this time may be green or have experienced colour change. Alternatively, misshapen seeds could be an indication of an aster yellows infection.

Next Steps

Harvest

When deciding to straight cut or swath, the goal is for 2 percent or less of green seed at grading time.¹ Straight cutting works better on thick stands of canola but should not be rushed before green chlorophyll colour has cleared seeds. Swathing should be considered for thin, drought-stressed stands. Because dry plants have a light structure, consider the following:

• Make swaths parallel to prevailing winds.
• Cut plants just below the lowest pod to keep stubble as high as possible.
• Press swaths into stubble with a lower adjusted swath roller.²

Seeds need at least 20 percent moisture to finish maturation and clear green colouration.¹ Continued hot, dry weather through harvest operations can lower seed moisture more rapidly than planned for combining.

Grading

Sprouted seed is considered damaged, and grain grades drop based on the total percentage of damaged seed.

• No. 1 canola has no more than 5 percent damaged seed.
• No. 2 canola has no more than 12 percent damaged seed.
• No. 3 canola has no more than 25 percent damaged seed.³

Storage

Sprouted canola should be dried down to 1 percent less than normal for storage conditions.¹ Low test weight grain could be expected in years with drought and heat stress. Shorter storage life is expected for grain with low test weights and poor integrity. The first weeks of canola storage are a time of high respiration, heat, and moisture. Aeration and cooling are critical during this early storage period.

Causes

Heat stress causes a reduction in the plant hormone ratio of abscisic acid to gibberellic acid and is likely the cause of sprouted seeds. The abscisic acid to gibberellic acid ratio plays a role in germination inhibition and seed maturation. Heat stress speeds up germination and causes seedling abnormalities.⁴

Endosperm and embryo development in canola seed are sensitive to high temperatures. Heat stress alters enzymatic processes and oil-protein ratios. Additionally, drought can reduce nutrient uptake and photosynthesis products.⁵ These stresses alone and combined lead to lower seed weights.

Continuous wet weather after seeds have dried to 10 percent can lead to sprouting.³ Maturation and dry down could be rapid during drought seasons. Hot (32°C), dry weather can cause canola to change colour from 10 to 50 percent in three to five days or less. Weather favouring drying can lead to seed moisture loss at a rate of 2 to 3 percentage points per day or greater.¹ Areas receiving rains after this maturation and dry down have rewetting as a possible cause for precocious seed sprouting.

Aster yellows is caused by a specialized bacterium called phytoplasma. The disease has a low infection rate (1%) for most fields most years.⁶ Aster leafhoppers transmit the disease, and greater populations of the insect have been reported in the United States during hot, dry weather.⁷