In the southern portion of the state, above-average temperatures have resulted in winter wheat remaining green (see picture). Will the vernalization requirement be met?
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 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). Temperatures above 64°F were ineffective for vernalization. Although winter wheat is green and the winter temperatures have been fairly mild, winter wheat should meet the vernalization requirement.
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. In our research, at Feekes 6 growth stage (first node visible), winter wheat yield was reduced when temperatures reached 14°F for 15 minutes. As winter wheat continue to grow, the plant has a decreased tolerance to freezing temperatures. At Feekes 8 growth stage (flag leaf visible, but still rolled up), a temperature of 19°F for 15 minutes reduced grain yield.
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.