Frost Injury in Wheat
In 2004, frost injury had not been seen in the southwest for over 20 years but here we are two years later and again we are talking about an early spring frost! This article has been modified and originally appeared in the May 7, 2004 Crop-Pest Ontario Newsletter issue.
Although today's winter wheat varieties can tolerate very low temperatures during the winter, their ability to tolerate (hardiness) low temperatures decreases significantly when growth continues in the spring (Figure 1). When the frost (cold injury) occurs is very important (Table 1). Injury during the tillering stage does not normally impact yield since the growing point is protected (below ground). Leaves are often twisted, hooked, light green to yellow in colour with burned (necrotic) leaf tips (Figure 2). In some fields, frost injury is evident with newly emerging leaves unable to expand properly, and exposed leaves showing injury similar to "sun scald" in corn.
Leaves injured by spring frost appear at first water-soaked, then dark green. These injured leaves dry out and quickly turn brown. This type of injury had not been seen in the southwest for over 20 years!
Although, growth may be delayed for a short period, new leaves and tillers will emerge and growth will continue under favourable conditions.
In addition, there are differences in variety tolerances to low spring temperatures and cold injury symptoms will often be more obvious in these varieties and may reduce vigour and yield in these varieties. If you are concerned about a particular variety contact your seed dealer.
As the wheat plant moves into the stem elongation (jointing) growth stages (Zadok's 31 to 47), low temperatures can result in significant damage since the growing point (head) is no longer protected. It is in these most advanced wheat fields in the southwest where significant injury has occurred. The growing point should be examined in these fields. In addition, frosts that occur during tiller elongation can cause the collapse and death of young growing (meristematic) tissues immediately above and below nodes.
The growing point will be just above the uppermost node. Take a sharp knife and split the stem lengthwise. If the growing point is bright yellow-green and firm then it is fine. However, if it has a water soaked (wet) appearance, mushy or has become off-white or brown, damage has occurred. Do not just rely on leaf symptoms, examine the growing point.
Figure 4 - A yellow or necrotic leaf emerging
Figure 5 - Examine growing point - Texas A&M
Figure 6- Growth Stages of the Wheat Plant (Courtesy of Nebraska State University)
Seedling Stage is the growth stage from wheat emergence until the
plants begin to tiller.
Another factor that should be taken into consideration in your decision to keep or replant to another crop (corn preferably for rotation purposes) is uneven maturity. Mild or partial injury can result in slightly decreased yields but more importantly many late tillers will develop that will mature later then the normal or unaffected tillers. If Fusarium head blight becomes an issue this year, the differences in heading dates could make it difficult to time a Folicur application.
Although the three or four cold nights during the week of April 24th may have caused some frost injury it appears less then what was seen in 2004 when frost occurred as late as May 4th. In 2004, the majority of these fields (95%+) recovered quickly with minimal adverse effects.
That is if the growing point was not exposed to freezing temperatures, therefore the growing point of the most advanced wheat however needs to be examined. Stake the damage areas and keep an eye on them for the remainder of the season.
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