Updated: May 18, 2023
With temperatures dipping below zero in much of the province last night, many are wondering what effect this will have on cereal crops.
What temperatures will cause injury?
Figure 1 shows the various wheat growth stages and when injury is likely to occur to the crop after experiencing cold temperatures for a two hour duration. Other crops such as triticale and rye are slightly more cold tolerant while spring cereals such as oats and barley are more sensitive. However, they are less sensitive to cold injury currently based on their growth stage relative to planting date.
Figure 1: Temperatures (°F) that cause injury to winter wheat at various stages after two hours duration. Graph adapted from A.W. Pauli.
The amount of injury that occurs is highly dependent on the growth stage of the crop and the amount of time the crop is exposed to the cold temperatures. The later the growth stage, the greater risk of injury at low temperatures. Soil mositure can also have an impact with dry soils being more prone to temperature fluctuations because they give off built up heat quicker.
Most of the winter wheat crop in the province is at growth stage(GS) 30 (stem elongation) or less while most spring cereals are not yet at the tillering stage. Fields that are up to GS29 (tillering), can withstand temperatures as low as -11°C (table 1). Once temperatures fall to -11°C injury can be identified by leaf tip burning and chlorosis as well as a silage odour. Temperatures are not expected to get that low so the risk of injury is relatively low. However, those fields currently at stem elongation or the jointing stage (GS30), are less tolerant to cold temperatures. Once at the jointing stage cereals are susceptible to injury if temperatures fall to -4°C for two hours or more. At this point death of the growing point can occur with splitting or bending of the lower stem and leaf yellowing or burning. Yield losses with cold temperatures at this stage can be anywhere from moderate to severe.
Table 1: Temperatures that cause freeze injury to wheat at spring growth stages and symptoms and yield effect of spring freeze injury (Source: Spring Freeze Injury to Kansas Wheat, Kansas State University. 1995)
| Growth Stage | Approximate Injurious Temperature (2 hours) | Primary symptoms | Impact on yield |
|---|---|---|---|
| Tillering | -11°C | Leaf chlorosis; burning of leaf tips; silage odor; blue cast to fields | Slight to moderate |
| Jointing | -4°C | Death of growing point; leaf yellowing or burning; lesions, splitting, or bending of lower stem; odor | Moderate to severe |
| Boot | -2°C | Floret sterility; head trapped in boot; damage to lower stem; leaf discoloration; odor | Moderate to severe |
| Heading | -1°C | Floret sterility; white awns or white heads; damage to lower stem; leaf discoloration | Severe |
| Flowering | -1°C | Floret sterility; wheat awns or white heads; damage to lower stem; leaf discoloration | Severe |
| Milk | -2°C | White awns or white heads; damage to lower stems; leaf discoloration; shrunken, roughened, or discolored kernels | Moderate to severe |
| Dough | -2°C | Shriveled, discolored kernels; poor germination | Slight to moderate |
When should I assess my fields?
Assessing cereal fields after frost should occur after a few days of warm temperatures. At that point any injury will become more evident. Fields with the most advanced cereal crop should be checked first as they are most at risk. Assess low lying areas, especially if the nights were still with little to no wind. Kansas State, Texas A&M and Purdue have some good photos showing freeze injury to cereals. Dennis Pennington from Michigan State has also recently posted a video on how to scout your fields for frost injury which can be found here:
Kansas State Spring Freeze Injury: https://bookstore.ksre.ksu.edu/pubs/c646.pdf
Wheat Freeze Injury in Texas: https://cdn-ext.agnet.tamu.edu/wp-content/uploads/2019/06/ESC-026_-Wheat-Freeze-Injury-in-Texas.pdf
Field Crop Disease Update 2020: Wheat – Accurate Diagnosis Of Potential Injury, Viruses, Or Other Issues In Wheat: https://extension.entm.purdue.edu/newsletters/pestandcrop/article/field-crop-disease-update-2020-wheat-accurate-diagnosis-of-potential-injury-viruses-or-other-issues-in-wheat/
How to Scout Your Field for Frost Injury: https://www.youtube.com/watch?v=RWBJHKZbjps&feature=youtu.be