‘Warm’ Winter Days…What This Means for Wheat

Across Ohio, the average air temperature was 8-10°F warmer in January and February (so far) (Table 1). Due to these warmer winter temperatures, wheat may appear greener than usual and also raises the question, “Will the vernalization requirement be met?”

Table 1. Average air temperature in Wood County, Wayne County, Clark County, and Pike County, Ohio in 2023 compared to the normal. (Data from the CFAES Weather System)

Winter wheat has molecular regulation preventing the transition to reproductive growth until a certain threshold of cold days has been reached. This regulation is called “vernalization.” In winter wheat, the vernalization period protects plants from breaking dormancy too early. The vernalization requirement varies among wheat cultivars and is temperature and day length dependent. In a study conducted on one winter wheat cultivar, it took 40 days for plants to achieve vernalization at 52°F while it took 70 days for plants to achieve vernalization at 34°F (see Figure 1). Temperatures above 64°F were ineffective for vernalization. Although winter wheat is green and the winter temperatures have been above average, the vernalization requirement will be met.

Once the vernalization requirement has been met, growth is driven by growing degree units. At this point, exposure to freezing temperatures can be a concern. However, in our research, even at Feekes 6 growth stage (first node visible & above the soil surface; usually mid to late April), winter wheat yield was not reduced until temperatures reached 14°F for 15 minutes. As the winter continues into spring, we will address this issue in future newsletter articles as needed.

Figure 1. Number of days to meet vernalization requirement of winter wheat. (Figure adapted from Brooking, 1996)

References:

Alt, D.S., Lindsey, A.J., Sulc, R.M., & Lindsey, L.E. (2020). Effect of temperature on survival and yield components of field-acclimated soft red winter wheat. Crop Science, doi: 10.1002/csc2.20087

Brooking, I.R. (1996). Temperature response of vernalization in wheat: a developmental analysis. Annals of Botany, 78, 507-512.