Boot: In the boot stage, wheat can be injured if temperatures drop down into the mid to upper 20s for several hours. Injury is more likely if this occurs repeatedly and if it is windy at night. To detect injury, producers should wait several days then split open some stems and look at the developing head. If the head is green or light greenish in color and seems firm, it is most likely going to be fine. If the head is yellowish and mushy, that’s a sign of freeze injury.

Awns beginning to appear: If the awns have begun to appear, there can be significant injury to the heads if temperatures reach about 30 degrees or lower for several hours. Tillers may finish shooting up the head, but few, if any, spikelets may pollinate normally and fill grain. Damaged heads from a freeze at this stage of growth may seem green and firm at first glance, but the floral parts will be yellowish and mushy.

Heading. Wheat is particularly vulnerable to damage from freezing weather as the head starts to emerge through the flowering stage. Temperatures of 30 degrees or lower can damage anthers if they are exposed.

If the wheat was in the flowering stage at the time of the freeze in the early morning hours of May 16, you can determine if the anthers are damaged by examining them with a magnifying lens, the K-State agronomist said. “Healthy anthers will be lime green. If they are damaged by a freeze, they will begin twisting within 2 to 3 days. Shortly afterward, they will begin to turn whitish or brown. The stigma in the florets also may or may not be damaged by a freeze. If the anthers are damaged by freeze, the flowers may fail to develop a kernel,” Shroyer explained.