Last week, temperatures in northern Ohio dipped below freezing prompting some concerns about possible injury to the wheat crop.
The effect of cold weather depends on the wheat growth stage. Maximum resistance to cold weather occurs in December-February. As wheat greens-up, the plant becomes less tolerant of freezing temperatures (see wheat freeze chart), which could be particularly damaging after jointing when the growing point is above the soil surface.
Currently in Ohio, most wheat is between the Feekes 5 (green-up) and Feekes 6, aka “jointing”. At the Feekes 6 growth stage, temperatures of ≤24°F for at least two hours may be injurious. However, even at Feekes 6, the growing point is still near to the soil surface and is somewhat protected by the vegetation. Injury is most severe when wheat is at the boot and heading growth stages.
If you think your wheat has been affected by freeze injury, wait a few days after the suspected freeze to observe the injury. Walk the field and look for discoloration and deformations. Between Feekes 6 and 8, leaves and stems on freeze-damaged plants become twisted and turn light green or yellow with necrosis (death) of the leaf tips. At Feekes 8, the emerging flag leaf appears yellow or necrotic instead of healthy green, indicating that the growing point is damaged or killed. Secondary, unaffected tillers will develop and produce grain, but tillers with damaged growing points will stop growing and will not produce a head.
References: Shroyer, J.P., M.E. Mikesell, and G.M. Paulsen. 1995. Spring Freeze Injury to Kansas Wheat. Agricultural Experiment Station and Cooperative Extension Service. Available at: http://www.ksre.k-state.edu/bookstore/pubs/C646.PDF