Check crops today after frost

September 17, 2010 — Did you have frost last night? Growers with standing canola are wondering whether to swath right away. Before making that decision, note the temperature and duration of the frost.

If you had a heavy frost… below -2 C

Go out early this afternoon and assess the damage. Canola may wilt and desiccate quickly after this heavy frost, depending on factors such as crop stage, duration of frost and field topography. Check pods for a white, wilted  appearance. Pod shatter and pod drop could begin within a day, especially with warm sunny afternoons. If pods are desiccating rapidly, swathing right away will preserve as much yield as possible.

Heavy frost is considered anything below minus 2°C. Many parts of north central Alberta and northwestern Saskatchewan were down to minus 5°C or lower this morning and had been cold for many hours. The photo below shows canola pods that experienced a minus 7°C frost this morning. The pods have already turned translucent, a sign of heavy frost damage.

If you had a light frost… above -2 C

Hold off swathing. Check this afternoon for wilting to make sure frost damage was not heavier than expected. You may see some speckling on the stem and pods, but this is of no concern as long as the plant is still alive. If no wilting, leave the crop standing and check daily.

What to look for during daily monitoring:
—If the majority of the seeds remain turgid, delay swathing to allow for further seed maturity.
—If the pods are severely damaged and are beginning to desiccate, swath during periods of dew or high humidity to reduce the amount of pod shelling and pod drop.

Why wait? The amount of frost damage depends on various factors including crop stage, degree and length of frost, relative humidity, and presence of rain or dew. In many cases, a light frost will damage the outside of pods but seeds can continue to mature — increasing yield and quality — if the crop is left standing.

Frost and quality. A killing frost will reduce quality, but that can’t be helped — whether you swath today or wait. Immature seeds (moisture content higher than 20%) will be damaged. Seeds with less than 20% moisture will normally escape damage. Green seed is the major downgrade that results from frost.

If you have further questions, click the name of the Canola Council of Canada agronomist in your region and send an email.

Derwyn Hammond, Manitoba
Jim Bessel, North Central and North Eastern Saskatchewan
Tiffany Martinka, Eastern Saskatchewan
Clint Jurke, Western Saskatchewan
Troy Prosofsky, Southern Alberta
Doug Moisey, North East and East Central Alberta
John Mayko, West Central Alberta
Erin Brock, Peace Region