OMAFRA Report: Impact of a late spring frost on canola

Ontario winter canola yields were very strong in 2020 giving us a good look at the incredible yield potential of the crop. Many producers reported yields over 3,700 lb/ac and some watched their yield monitors jump over the 5,000 lb/ac mark. The mild winter was likely a big part of that success, but Mother Nature did put the crop through an important test – late spring frost.

During the last week of April, most winter canola growing regions were seeing temperatures above 15°C, and as high as 20°C in some areas. The canola was developing flower buds and elongating, advancing quickly towards first flower. May 8 to 13 was a much different story, however, and for a few days in a row the temperature fell below zero. In Harrow, the temperature dropped to -6°C on May 8 and stayed below zero for over 24 hours. Top yielding fields in Blenheim also saw temperatures as low -4°C and spent many hours between zero and -3°C over a five-day period. Other winter canola fields, such as those in Prince Edward and Perth Counties reached similar lows but for fewer hours.

Winter canola can tolerate low temperatures while in vegetative stages. Injury caused to canola by cold conditions during late vegetative stages in spring include:

    frost injured leaves

– heaving and rotting where there is excess moisture or high clay content;

– death of main growing point and subsequent development of multiple stems; and

– frosted plants killed in tire tracks when fertilizer was applied.

Reproductive structures are much more sensitive to extreme temperatures. Producers and seed companies have reported many examples of canola dying or being severely damaged when frost occurred during flowering in past attempts at winter production in Ontario. Many fields were scouted for injury in May 2020 and the impact of frost was relatively limited. Symptoms caused by cold temperatures during reproductive growth stages observed in 2020 include:

– drooping plants that stand back up when temperatures rise;

– open flowers and newly formed pods that abort/fall off;

– flower buds that abort/fall off;

– purple buds, pods and stems; and

– cracked stems.

The fields that were most advanced in early May lost some buds, flowers and early pods. Overall, the number of damaged reproductive structures was relatively few and did not result in significant loss. Losses in early flowering stages occurring on the main stem may be compensated for with branches and flowers that come later. There were many fields in 2020 that were just about to flower when cold temperatures hit, and they simply sat until warmer temperatures arrived and they were able to continue advancing through flowering.