Large amounts of freezing rain, sleet, hail, etc. hit the Oklahoma wheat belt on April 10, 2013 and temperatures are expected to drop to the mid to upper 20’s this evening (I posted a couple of pictures below). Wheat development ranges from early heading in southern Oklahoma to just past jointing in northern Oklahoma and the Oklahoma Panhandle. If forecasts are correct, wheat tillers in southwest Oklahoma that escaped the first freeze have a good chance of being taken out by this freeze. Central and northcentral Oklahoma has quite a bit of ice-covered wheat. Ice-covered wheat will remain at approximately 32F and this might be just warm enough to escape severe injury. If the ice melts, however, and temps drop into the 20’s even wheat that is just past the jointing stage can be injured. At this stage it is certain that we will have some freeze injury to the majority of the Oklahoma wheat crop, but it will be a good 7 – 10 days before we can accurately assess the level of injury.
I have been asked if there is a 1:1 relationship between % freeze injury and % grain yield loss. Generally, the answer is no. DISCLAIMER — the values I am about to discuss are approximations and have huge margins of error — An otherwise healthy wheat crop that sustains 10% freeze injury prior to boot would probably suffer yield losses in the order of 0 to 5%. This is because the plant will divert resources to the remaining wheat heads. If damage is sufficient to reduce the final head count below a critical mass (around 400 heads per square yard) the relationship between % freeze injury and % yield loss will be much closer. So a 60% freeze injury might result in a 40 – 50% loss in grain yield. Again, these numbers are rough estimations and environmental conditions following the freeze will greatly impact the plant’s ability to compensate after freeze.
Advanced wheat partially covered by ice at Okarche, OK. Photo courtesy Mike Schulte, Oklahoma Wheat Commission
Mixture of ice and rain on wheat at Banner Rd. and I 40. Photo courtesy Mike Schulte, Oklahoma Wheat Commission
Ice covered wheat in the Alva area. Photo courtesy Woods County Extension Educator, Greg Highfill
World of Wheat 
[…] Freezing temperatures and ice descended on young wheat crops in Kansas, Oklahoma and the Texas Panhandle this week, potentially causing severe damage throughout the region. It will be a few weeks before the extent of the damage is known. Kansas Wheat offers more details about the effects in that area on its Wheat Beat blog, at http://thewheatbeat.wordpress.com/2013/04/10/from-the-field-freeze-wreaks-havoc-on-kansas-wheat-crop/. Jeff Edwards, the small grains extension specialist at Oklahoma State University, wrote about the freeze at https://osuwheat.com/2013/04/10/spring-freeze-part-deux/. […]