No. 3/April 11, 1997
Cold Temperatures on Wheat
Although the wheat year has been quite good so far, with normal or slightly more than normal spring growth, temperatures around 20°F the morning of April 9 have many people worrying about freeze injury on wheat. In Illinois, the wheat crop growth stage ranges from barely past green-up (Feekes growth stage 4) in the northern border to Feekes 7 in the southern extremity. Feekes 4 is still in the tillering stage; while at Feekes 6, growth is mostly upright and the first node ("joint") can be felt at the base of the plant. At Feekes 7, the second node can be felt. The developing head is located at the tip of the stem, so it is exposed once jointing takes place.
Although freezing may kill some of the upper leaves, our main concern at this point is the possibility of freeze damage to the developing head. Information from Kansas shows moderate yield losses when wheat at jointing experiences 2 hours at 24°F. What differences we in Illinois might have with Kansas are probably in our favor: more top growth to insulate the head from night temperatures, and more soil moisture to hold up temperatures beneath the canopy. The loss of leaf area that we'll see might hurt yield potential some, and I would expect new leaves coming out in the next weeks to show some bleaching and damage due to having been frozen before emergence. You will want to split stems to check on the appearance of the developing head, and continue to monitor the color of the crop in the next few weeks.
Emerson D. Nafziger, Department of Crop Sciences (217)333-4424