By: Laura Lindsey, Alexander Lindsey, Aaron Wilson. OSU Extension. Originally published in OSU Extension C.O.R.N. Newsletter.
Every year presents a different set of challenges for agricultural production across Ohio. Last year, northwest and west central Ohio could not escape the rain. This year, Ohio cannot seem to shake the chill. An unusual weather pattern set up across the Midwest and Northeast U.S. late last week and into the weekend that led to some snow in spots and record or near-record lows across the state (Figure 1). Overnight lows for a few locations in Ohio on Saturday May 9, 2020 include 26°F outside of Toledo, 27° in Lancaster and Youngstown, and 28°F in Dayton, Cincinnati, and New Philadelphia. Many areas spent more than eight hours below 32°F with about 4 hours spent below 30°F. Naturally, this would raise questions concerning potential wheat damage.
Figure 1. Daily overnight lows based on station observations for May 9-10, 2020. Figures generated at Midwest Regional Climate Center.
Injury to winter wheat depends primarily on three factors: 1) growth stage, 2) how cold, and 3) duration of cold temperature. Differences in freeze injury among cultivars can usually be attributed to slight differences in growth stage.
At Feekes 8 growth stage (flag leaf visible, but still rolled up), the growing point is above the soil surface, but still protected within the crop canopy. Freeze damage at Feekes 8 growth stage can injure developing heads and damage the flag leaf. Symptoms of freeze damage include yellowing or browning (necrosis) of leaves. Once wheat enters Feekes 9 growth stage (ligule of flag leaf visible), the flag leaf may appear twisted (Figure 2). As the wheat head emerges, it can get stuck in the leaf sheath, causing a crooked appearance at heading (Figure 3). In our research, wheat grain yield was reduced, when the temperature dropped below 25°F for 15 minutes. According to research from Kansas State University, 28°F for two hours can cause moderate to severe reduction in wheat grain yield.
Figure 2. Twisting or spiral appearance of the flag leaf can be a symptom of damage from low temperatures.
Figure 3. Freeze damage may include browning or yellowing of the flag leaf. The wheat head may get stuck in the leaf sheath causing a crooked appearance at heading.
At Feekes 10.5.1 growth stage (beginning flowering), wheat heads are above the plant canopy, resulting in heads and anthers that are exposed with limited protection from the crop canopy. Freeze injury at Feekes 10.5.1 can cause sterility, embryo death, or complete loss of the spike. At Feekes 10.5.1, spikelets and awns may appear white or bleached in color as a result of cold temperatures (Figure 4). In our research, wheat grain yield was reduced, when the temperature dropped below 28°F for 15 minutes. According to research conducted at Kansas State University, at 30°F for two hours, winter wheat grain yield can be severely reduced.
Figure 4. Wheat spikelets and awns may appear white or bleached in color as a result of cold temperatures at Feekes 10.5.1 growth stage
Assessing damage. In the above map (Figure 1), temperatures dropped between 25 to 30°F between May 9 and 10. At these temperatures, wheat between the Feekes 8 and Feekes 10.5.1 growth stage may have freeze injury. It is important to assess fields for damage as damage may be more or less extreme depending on the growing environment (landscape features, soil moisture, wind speed, overall condition of the field, etc). We suggest waiting about a week to walk fields and look for symptoms of damage similar to what we have pictured here.
References:
Alt, D.S., A.J. Lindsey, R.M. Sulc, and L.E. Lindsey. 2020. Effect of temperature on survival and yield components of field-acclimated soft red winter wheat. Crop Sci. 60:475-484. https://acsess.onlinelibrary.wiley.com/doi/full/10.1002/csc2.20087
Shroyer, J., M. Mikesell, and G. Paulsen. 1995. Spring freeze injury to Kansas wheat. Kansas State Univ. Ext. Serv. https://bookstore.ksre.ksu.edu/pubs/c646.pdf