- Wheat is most susceptible to freezing temperatures in boot-heading stages
- The lowest temperature reached, and amount of time spent at those low temperatures are critical considerations
- Symptoms vary based on growth stage, but identification is important to avoid improper management decisions
While rising temperatures in April often signal the kickstart of the growing season, keep in mind that a late frost can be detrimental to a wheat crop. This article will discuss potential issues associated with a spring freeze on wheat and what you can do to assess potential issues.
Winter wheat is a crop that can tolerate cold temperatures during the early phases of its growth and development. From early developmental stages through tillering, this small grain can easily withstand temperatures of 12°F. However, as spring progresses and the wheat growth advances past stem elongation, it becomes more susceptible to injury by freezing temperatures and the length of time sub-freezing temperatures occur. This is because at jointing the growing point (meristem) is pushed above the soil surface and is no longer protected by the soil. Cold tolerance is reduced further from boot (28°F) through heading (30°F). The table below provides some detailed criteria for considering injury likelihood and symptoms to look for regarding sterility and poor grain fill.
Table 1. The effects of freezing temperature on wheat yield, as impacted by growth stage. Information based on Spring Freeze Injury to Kansas Wheat https://bookstore.ksre.ksu.edu/pubs/c646.pdf
| Growth STage |
feekes |
approximate temperature for injury (2 hrs OF |
Symptoms |
Effect on yield |
| Tillering |
1-5 |
12 |
Leaf tip scorch, blue cast to fields |
Low |
| Jointing |
6-7 |
24 |
Leaf chlorosis, splitting of lower stem, death of growing point |
Medium/High |
| Boot |
10 |
28 |
Floret blanking, spike trapping, leaf discoloration |
Medium/High |
| Heading |
10.1-10.5 |
30 |
Floret blanking, white awns/spikes, leaf discoloration |
High |
| Flowering |
10.51-10.54 |
30 |
Floret blanking, white awns/spikes, leaf discoloration |
High |
| Milk |
11.1 |
28 |
White awns/spikes, leaf discoloration, shrunken/discolored kernels |
Medium/High |
| Dough |
11.2 |
28 |
Shriveled discolored kernels |
Low/Medium |
If your wheat has experienced injury from freezing temperatures, it will often show symptoms within 3-5 days. Areas that are most likely to be damaged are low lying areas of the field, areas bordering forest edges, or other sources of shade. Light frost injury will cause the leaf color to turn yellow or light green while more severe injury will turn leaves darker green. Warm temperatures in the days immediately following a freeze may result in rapid plant growth, causing wheat head distortion and twisted appearance. Also, secondary tillers may be permanently stunted and not produce as well as they would normally. These symptoms can often be mistaken for diseases or nutrient deficiencies, and they may not be visible from a distance. For example, twisted awns or flag leaves may be confused with copper deficiency, while bleached glumes may appear similar to head scab or take-all. Therefore, it’s advisable to walk fields a few days after a frost event to identify damaged areas so that they are not misidentified.
If your grain was intended to be used for bread or seed for next season, it will be important to critically examine grain heads post-flowering. Kernel quality (or blank heads) and poor germination rates may result in the wheat being unacceptable for use in either purpose. It is unlikely that growers will experience a total crop loss, but the overall revenue value and end purpose can certainly be greatly affected.