Frost has left a swath of damage from northeastern Alberta to southern Manitoba, and a lot of questions for farmers wanting to salvage as much of this year’s crop as possible.
The large but late crops were hit with as much as four degrees Celsius of frost Aug. 19.
Canola growers would normally be counting the crop’s percentage of green seeds to determine swathing timing. However, the frost may cause some of those seeds to keep their unripened colour indefinitely.
“As little frost as zero degree can cause those seeds to stay green,” said Murray Hartman of Alberta Agriculture.
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“By now, there should be some shrivelling in those seeds though, and producers could count them out when trying to decide about swathing.”
Frost damage first appears in canola a few days after the event when pods start to appear white and speckled. Some green seeds will shrivel while others will turn dark green.
Leaves are more resilient to frost and can withstand temperatures as low as Ð6 C.
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.
“That’s when you want to wait to swath. Look for seeds that are maturing normally,” said Hartman.
“Frost like was experienced in Saskatchewan and Manitoba will have killed those seeds with 50 or 60 percent moisture. If they were under 20 already, it won’t be as much of a problem.
“But there weren’t that many crops at the 20 percent level yet,” he added.
Green colour that doesn’t clear from the seed is due to destruction of the enzymes needed to break down the chlorophyll.
John Mayko of the Canola Council of Canada recommends producers balance the maturity of the crop against any predictions of frost and swath two to three days in advance.
The advanced cutting will cause the seeds to begin desiccating and hopefully complete the transition from their immature green state.
Canola crops that are heavily frost affected should be harvested as soon as moisture conditions and maturity allow, because the pod tissue will desiccate rapidly and shelling out of seed will quickly become a problem.
Sherrilyn Phelps of Saskatchewan Agriculture said flax can have serious frost damage when the temperature is Ð3 to Ð5 C depending on the development of the bolls. She said if the crop has reached the dough stage, it could be quite resistant to cold.
Hartman said among the cereals, malt barley in Saskatchewan and Alberta may have suffered the most.
“As long as it hasn’t killed the seed it might still be selected, depending on the rest of the harvest’s quality,” he said.
Cereal plants exposed at the late dough stage can show little or no damage, while those at the early dough stage will desiccate quickly and undergo severe shrivelling.
Phelps said frosts of between Ð6 and Ð8 C can cause serious drops in germination rates in cereals that were in the early dough stages.
For most cereals, damage doesn’t fully show itself until seven to 10 days after the frost.
Phelps said pulse crops could be damaged in the podding stage by temperatures of Ð4 or Ð5 C, depending on the seed moisture.
Damaged seeds will be water soaked and soft to the touch.
Harvesting decisions about pulses should be based on the lower and middle sections of frost-damaged plants because these are the most mature and may have little or no damage from a mild frost.
Moisture of the overall crop, too, should be evaluated.
Hartman said the “last thing you need is heating or insect problems with grain that already will bring you a poor return because of frost damage.”
Manitoba Agriculture says corn is usually damaged by temperatures of Ð2 C or lower. Severity of damage depends largely on the duration and extent of freezing temperatures.
Corn is usually physiologically mature 50-55 days after the 50 percent silking date. Colder temperatures will kill the entire stalk. If only leaves above the ear are frosted, kernel development will continue. If the entire stalk and leaves are frozen, kernel development will cease and soft shriveled corn will result.
If corn is at around 35 percent moisture or if a black layer has formed at the base of kernel, the plant is physiologically mature and kernels will develop normally despite frost.
Frosted immature corn is best used for silage or fodder.
