Symptoms of Cold Damage to Wheat

Tillering

• The first broad phase of growth is known as tillering, named for of the initial emergence of tillers -- shoots that stem from the first buds of the plant. Tillering occurs in the fall, not long after planting, and coincides with winter dormancy during which most root growth takes place. However, when temperatures drop below 12 degrees Fahrenheit it causes some deterioration that can slightly or moderately affect the overall yield. Examples of these symptoms include twisting and loss of chlorophyll in the leaves, burning of leaf tips, a strong fragrance of dehydrating vegetation and an overall bluish hue in the fields.

Jointing

• This era of the plant's life is when the stem begins to elongate and its constituent segments, known as internodes, become more visible. Upper stem internodes lengthen ahead of their lower stem counterparts. Jointing is an early spring occurrence, but if a cold snap brings air temperatures to 24 degrees F the crop may experience moderate to severe cold damage. Within the stem are organs known as growing points, damage to which can terminate plant growth. Evidence of injury is obtained by bisecting the stems of a few sample plants and checking the points' color. Healthy wheat will have yellowish-green growing points; damaged crops will have a brownish color and appear waterlogged on the inside. Other symptoms of injury are burned leaves, lesions, a decaying odor and a split or bent lower stem.

Boot

• This is when the developed head of the wheat is covered by the flag -- or top -- leaf on its way to full emergence. Temperatures of 28 degrees F is enough to do moderate to severe violence to the wheat crop during this phase. The effects include sterile florets, which are impervious to pollination, emerging from the head. Head spikes may tear or rupture the boot (the protective head leaf), the lower stem may incur damage and the leaves will suffer discoloration. In addition, the smell of dehydrating flora will continue.

Heading and Flowering

• The stage during which the head emerges from its flag leaf cover is referred to as heading. Shortly after full emergence, pollination commences on the head; this is when the flowering stage begins. Anthers, the receiving organs for pollination, protrude from the head's florets, as do stiff protective bristles called awns. If temperatures dip below the freezing point during flowering, the normally green awns will take on a bleached white appearance, lesions will develop on the lower stem, frost rings will form where the leaves meet the stem and the leaves will suffer further discoloration.

Milk and Dough

• The final two stages relate to the formation and maturity of kernels in late May or early June, just prior to harvest. The threshold for cold damage is a rare 28 degree F which, if reached, can wreak havoc on the crop. Kernel growth can be stunted, appearing shrunken, shriveled and discolored. Worse, the cold may result in poor germination and an overall reduction of kernels. The good news, however, is that once the plant has passed from milk to dough, its resistance to cold and its general vigor are high. Other than some slight shriveling at the stem, a fully matured wheat plant will suffer only slight injury from freezing temperatures.