Recently, temperatures dipped to the low to mid-30s in the southern portion of the state and high 20s in the northern portion of the state. Of course, this brings potential concern about winter wheat, which is between Feekes 6 (first node visible) and Feekes 7 (two nodes visible) in the north and Feekes 8 (flag leaf visible) and Feekes 9 (ligule of flag leaf visible) in the south.
The magnitude of freeze damage depends on: 1) temperature, 2) duration of exposure, and 3) wheat growth stage. A few years ago, we conducted a freeze chamber experiment to examine the effect of low temperature on winter wheat at several growth stages (Table 1). Keep in mind, actual yield reductions in the field can be quite variable depending on the weather during the remainder of the growing season. At the Feekes 6 growth stage, temperatures >20°F caused no damage. However, by the Feekes 8 growth stage, temperatures of 25°F to 28°F caused a 10 to 25% reduction in wheat yield. These temperatures were collected from the crown of the wheat plant, not the air temperature.
Table 1. Temperature (15-minute duration) at which wheat yield was reduced by 5%, 10%, 25%, and 50% at Feekes 6, 8, and 10.5.1 growth stages. (Data from Lindsey et al., 2021).
|
Feekes growth stage |
5% reduction |
10% reduction |
25% reduction |
50% reduction |
|
 |
Temperature (°F) at Growing Point of the Plant |
|||
|
6 |
20.1 |
17.9 |
14.8 |
11.9 |
|
8 |
30.7 |
27.6 |
24.6 |
21.9 |
|
10.5.1 |
28.7 |
27.8 |
26.3 |
24.1 |
I don’t anticipate significant damage from the cold temperatures due to earlier growth stages in the northern part of the state and slightly warmer temperatures in the southern part of the state. However, farmers may want to assess their wheat crop when temperatures begin to warm up again. Make sure to examine several areas of the field as landscape features influence the micro-climates within fields. Small differences in temperatures can cause large differences in damage and grain yield.
At Feekes 6 growth stage, damage from freezing will cause discoloration of the leaf tissue, with leaf tips or edges exhibiting symptoms first (Figure 1). However, discoloration does not necessarily indicate a reduction in grain yield. At Feekes 6 growth stage, damage can also be assessed by carefully cutting the wheat stem lengthwise to expose the developing spike at the first node. Damaged spikes will appear discolored and shriveled. A healthy, developing spike should be rigid and whitish-green (Figure 2).
At Feekes 8 growth stage, damage from freeze may include yellowing or browning of the flag leaf. The flag leaf may appear twisted or in a spiral (Figure 3). As the plant continues to grow, the wheat spike may get stuck in the leaf sheath, causing a crooked appearance at heading. (Although, this phenology can also be associated with spikes that emerge quickly due to warm temperatures.)
For more information, see our ‘Freeze Symptoms and Associated Yield Loss in Soft Red Winter Wheat’ FactSheet: https://ohioline.osu.edu/factsheet/anr-93