The wheat varieties we grow in KY will respond differently to the extremely low temperatures we have experienced over the past few days. Several traits come into play but the most important thing
Most of the wheat varieties grown in KY develop at a rate that is determined by heat units accumulated, which we commonly refer to as Growing Degree Days (GDD). These varieties were pushed by the unusually warm temperatures we experienced in February, so that many of them had reached jointing (Feekes 6) or beyond when the severe freezes began. A much smaller percentage of our wheat varieties are held back by sensitivity to daylength. These daylength sensitive varieties will not joint until they reach a daylength threshold – i.e. a minimum no. of hours of daylight. Such sensitive varieties remain prostrate in their growth habit until the threshold is reached and thus the growing point remains near the soil surface and is much more protected than the growing point in an upright variety at jointing or beyond.
Many growers may find that their crop is not exactly prostrate, but not completely upright either. In this case it is best to take the steps to determine the extent of the damage – i.e. dissecting the stem to find the growing point. These methods will be covered at the Emergency Wheat School (March 21 at UKREC Princeton, KY or ZOOM Meeting https://uky.zoom.us/j/665243687) and in the Grain Crops Update Blog.