The title of this short article may seem a paradox, but leave it to a Minnesota spring to create the conditions for both problems within a day or two. Last night's lows may have caused some frost damage in northwest Minnesota. Fortunately, for spring wheat and barley the damage is cosmetic and will not require replanting. The reason for this is as simple as it is elegant. The tender growing point from which all leaves and eventually the spike is produced is insulated and protected by the soil. Up the approximately the 5-leaf stage the growing point is located at the crown at ± 1.5 inch below the soil surface. The crown is easy to recognize as a hard knob from which both roots as well as leaves start. This evolutionary adaptation to keep the growing point hidden and protected from the elements is precisely why small grains fit so well in this area. Frost damage will initially have a dark green, water soaked appearance that will quickly dry out, leaving the tissue white to tan (Photo 1). Frozen and dried up leaf tips will often break off with a little wind and give the field a very raged appearance. New growth should not show any symptoms.
Photo 2. Heat Canker on just emerged wheat.
The sunny, windy weather and big temperature swings expose the young seedlings to a second abiotic stress. The heat at the soil surface can cause heat canker. The tender young tissue at the soil surface basically will 'cooked' and this appears as a yellow band that is slightly constricted (Photo 2). As the leaf continues to grow, this yellow band (1/8 - 1/4") moves upward and away from the soil surface. If the conditions last for more than a day, repeated bands can become visible. As with freeze injury, the tips of leaves may break off at the yellow band and give a field a very ragged appearance. Damage from heat canker is temporarily and should not affect further growth and development.