Over the years we have observed the effects of spring freezes on canola at the bolting and flowering stages. We can draw on these experiences to speculate on how the recent freezes might impact the crop. The extent of the damage will ultimately depend on a number of factors including the low temperature reached, the amount of time below freezing, the growth stage of the crop, and other environmental factors such as soil moisture and exposure to the wind.
Some of the common damages include leaf burn and loss; stem cracking and splitting; bud, flower, and pod loss; and plant lodging. In some instances, the crop will suffer a yield penalty because the extent of the damage was too severe. In other instances, ideal growing conditions returned shortly after and allowed the crop to produce more flower buds, flowers, and seed pods, thus, a yield penalty was not observed. Canola is indeterminate (continues to flower and produce seed pods for an extended period) and because of this has numerous growing points on the plant. These growing points can develop new flowering sites that will compensate for damaged ones when stresses like spring freezes occur.
Growth stage can affect the extent of crop damage depending on how low and how long temperatures were below freezing. Canola is most tolerant to freezing temperatures in the rosette and bolting stages and more susceptible in the flowering and pod filling stages. This year, canola was in the early bolting to mid-flowering stages across the state. We have seen canola recover from freezes in the mid-20s over a 3 to 7-hour time period with little substantive damage at these stages. Temperatures below 20 for any extended period of time can be very damaging.
What are the indicators of injury to canola?
Cosmetic injury will be observed immediately but canola should begin to recover as soon as temperatures warm up. The time it will take to allow a more realistic estimate of the potential damage and recovery will depend on temperatures and moisture conditions, but should become apparent within 7 to 10 days.
Figure 1. Leaf discoloration was present in winter canola plots near Manhattan, KS after the recent spring freezes. The damage observed here is likely cosmetic in nature. Photo by Mike Stamm, K-State Research and Extension.
Figure 2. This variety is extremely susceptible to winterkill and winter decline syndrome, and is showing severe effects from the spring freezes. Photo by Mike Stamm, K-State Research and Extension.
Figure 3. Stem splitting can occur after spring freeze events. This becomes an entry point for fungi and future stem decay. Photo by Mike Stamm, K-State Research and Extension.
Figure 4. Flowering racemes are bent over following freeze events near Manhattan, KS. The red arrow is pointing to a wilted flower cluster that will likely dry up. Photo by Mike Stamm, K-State Research and Extension.
Figure 5. Canola varieties with greater winter hardiness, tolerance to winter decline syndrome, and later maturity tend to see less negative effects from spring freezes. This particular variety, KS4719, is a potential new release from the canola breeding program.
Longer durations of temperatures in the mid-20s may increase the severity of damage. The extent of damage and potential yield loss relative to how long it stays this cold is somewhat of an unknown. But as long as the plants show normal growth in the upcoming days and weeks, reasonable yields can be expected.
Long-term impact of freeze damage
Longer term effects on the crop include differential maturity, delayed maturity, and reduced plant height. Differential maturity may occur if the freeze wasn’t quite severe enough to completely kill the plant, and favorable conditions cause a secondary bloom to occur. Delayed crop maturity results in flowering and grain filling during a warmer period which can reduce yield if temperatures are above 90. If temperatures remain cool during flowering and early grain fill, yield reductions should be minimized. Reduced plant height doesn’t necessarily result in reduced yield.
The indeterminate growth habit still gives canola an opportunity to compensate for lost yield. How well the crop yields will be a function of the weather over the next few weeks.
Mike Stamm, Canola Breeder