[UPDATED: May 29, 2019]
*Spring wheat and barley are very tolerant to temperatures as low as -6 C because their growing points are below the soil surface until the five-leaf stage to jointing, Manitoba Agriculture’s website says.
While it’s often thought oats are just as frost-tolerant, barley and oat breeder Brian Rossnagel says that isn’t the case because the oat growing point is above ground during emergence.
“I have seen side-by-side oat and wheat fields in past years where a spring frost had no effect on the wheat and wiped out the oat crop,” Rossnagel, Distinguished Professor Emeritus at the University of Saskatchewan, said in an email May 29.
“Winter wheat at the tiller stage can withstand very low temperatures for a period of time (-11 C for less than two hours).”
Canola seedlings will usually recover from a light frost that can wilt leaves, but does not damage the growing point. The temperature where frost injury occurs varies with the plant’s growth stage, moisture content and the duration that temperatures are below freezing. For example, canola at the cotyledon stage is more susceptible to frost damage than plants at the three- to four-leaf stage.
Corn in the V5 stage (five leaves with collars showing) or less will recover from light frosts because the growing point is still below the soil surface.
While extremely rare, if air temperatures drop to -2 C or less for more than a few hours, the growing point region of a young corn plant can be injured or killed even if it is still below the soil surface.
The best way to assess frost damage to young corn is inspect and evaluate after three to five days.
Due to the variability of frost, evaluate on a field-by-field basis. Generally frost injury is more severe on fields with heavy residue.
Plant size matters, the website says. The smaller the soybean plants the more tolerant they are to frost.
Soybean plants that are just cracking through the soil (VE) and up to the cotyledon stage (VC) can tolerate -2.8 C for a few hours.
If the main growing point is killed by frost, the two axillary buds will start to grow within a week of the frost event.
Soybean plants that were still below the soil surface… will emerge normally.
Edible beans that have not emerged will not have been injured by the frost, the website says.
Edible beans are more sensitive to frost than soybeans.
Growers should wait four to six days to look for signs of growth from the main growing point and make a decision then.
MASC seeding deadlines
Farmers forced to re-seed due to frost damage still have lots of time before the crop insurance deadline for cereals and flax June 20.
The full coverage deadline for Argentine canola is June 15 and 10 in Canola Areas 1 and 2.
The Canola Area 1 and 2 deadlines for reduced crop insurance coverage is June 16 to 20 and June 11 to 15, respectively
The full coverage deadlines for grain corn is June 6 in Grain Corn Area 1 and May 30, in Grain Corn Areas 2, 3 and 4.
The full coverage deadlines for soybeans is June 6 in Soybean Area 1 and May 30, in Soybean Areas 2, 3 and 4.
See the complete list of crop insurance seeding deadlines, visit the Manitoba Agricultural Services Corporation website.
*UPDATE: The information for spring cereals was expanded, including an additional link for more information.