Frost coming, should growers swath?

With frost forecast for many Prairie regions by Thursday or Friday this week, many growers are wondering whether to swath canola today so the crop has 3 days in the swath to cure before the frost comes.

The goal of swathing canola ahead of a potential frost is to get the seed to dry down to below 20% moisture — the point at which the risk of seed damage from frost is minimized. Most regions are unlikely to get 3 warm, dry days, which is often what it takes for swathed canola to reach 20% moisture, between today and the forecast frost.

So should growers swath anyway and hope it dries enough?

The answer is “yes” if:

Seed has matured to at least 15% or 20% seed colour change on the main stem and if seeds are firm all the way to the top. The yield penalty from swathing this crop early will be relatively small. It may not dry down to below 20% but drying it down to 30% will cause less frost damage than staying at 45-50% — especially if the temperature gets down to -3°C or more. Swathing these crops today may help save the grade, and if the frost doesn’t materialize growers won’t have sacrificed too much yield.

Leave the field standing if:

Seed colour change is less than 10% with lots of watery seed in upper pods and pods on branches. These really green fields likely won’t dry down enough to completely protect them anyway. By leaving these fields standing, growers could see higher yields IF the forecast frost doesn’t materialize or isn’t severe.

Growers are also asking whether moisture on the ground protects canola from frost? It won’t hurt the crop, but as for a benefit, the short answer is “not likely.” It’s moisture on the crop — rain or heavy dew — that provides some protection from frost. However, lots of ground moisture should increase the chances of higher humidity and heavier dew.

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 Region
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