Varietal Differences in Freeze Damage

Dave Van Sanford, Wheat Breeding and Genetics, University of Kentucky and Bill Bruening, Small Grain Variety Testing, University of Kentucky

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 for the grower to consider at this point is growth habit, which can range from completely prostrate to very upright.

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 in the Grain Crops Update Blog.

Many public and private breeding programs are working to develop varieties that are sensitive to daylength (and protected from spring freeze) but still early to mid-season in maturity. This is a work in progress but we expect to see a number of these varieties released over the next few years.