Canola Watch: Heat stress | Canola pods growing?

How to support max yield as canola enters the homestretch?

The last weeks of the growing season offer critical opportunities to proactively influence yield and protect the crop. Insect scouting (especially diamondback moth, lygus and grasshoppers) is priority one. Insect populations can expand rapidly in hot weather so be continuously vigilant. There may be opportunities to improve crop fertility this year or to gain important knowledge to optimize fertility management next year. Tissue test strong and weak areas of the field. If adding late-season fertility, leave test strips to check ROI. (Thresholds for major canola insects) (Insect distribution and abundance protocols)

Why are canola flowers pale?

The most common reason for pale canola flowers is sulphur deficiency. Even if adequate sulphur exists in the soil profile, it may have been washed out of the root zone by early season moisture, especially if the crop didn’t root deeply. In addition to the characteristic small, pale-yellow flowers, look for small, narrow, often cupped top leaves, pale yellow new leaves, prolonged flowering if the crop has trouble setting seed, short pods with little to no seed set, and patchiness/variability across the field. Read more about sulphur deficiency here.

Less common reasons for pale flowers relate to herbicides:

• Glyphosate applied late and off-label (after the 6-leaf stage) on Genuity (not TruFlex) canola can cause pale flowers. In this case, look for near-white petals of normal size with short stamens that don’t protrude above petals in recently opened flowers. This article describes glyphosate damage to canola’s reproductive parts.
• Drift from group 27 Pyrasulfotole (Infinity) herbicide can turn flowers white. Damage looks striking but is generally minor.
• Cultivar off-types can also cause light-coloured petals.

Why is canola sprouting in pods?

There are three causes for ‘precocious germination’, or canola sprouting in the pod. We’ve listed them from most to least common for this time of year at average moisture conditions:

• Aster yellows causes all sorts of strange growth abnormalities. Later-season aster yellows infection can appear as sprouting in pods, sometimes without any other obvious symptoms. In many cases, these misshapen or malformed seeds will dry up and blow out of the combine at harvest.
• Drought stress can cause a hormone imbalance that causes seeds to sprout in pods and cut plants to regrow.
• At the end of the season, canola can sprout in a standing row if seed moisture drops down to around 10% moisture then gets wet again (this is much less common in canola than in cereals).

(Sprouting canola seed causes) (Aster yellows) (Sprouted canola seed grading guide)

How does heat stress impact different crop stages?

Ongoing heat continues to take a toll on canola. Here’s how:

• Vegetative stage: heat stress can impact growth rate, nutrient acquisition (if water demands are not met), and the ability of the crop to produce the energy that will ultimately drive seed production.
• Rosette, pre bolting, bolting: heat stress can cause hormonal imbalance
• Flowering: heat stress reduces seed number because the pollen grain is not hydrated on the stigma, which reduces fertility and decreases seed production
• Seed fill: heat stress can decease movement of sugars and other raw material from the mother plant to the developing seed, resulting in smaller seed and potentially lower seed quality.

Yield is based on seed number (determined at flowering) x seed size (determined at seed fill). Seed number contributes more to yield than seed size, so yield is most impacted by heat stress during flowering, especially early flowering. Older varieties are more sensitive to heat stress than newer ones. (Heat at flowering)