By Laura Lindsey
We’ve received a few reports of white (or bleached) wheat heads which can be a result of freeze damage or disease.
Freeze damage. In mid-May temperatures dipped to high 20s/low 30s in several parts of the state. At heading-flowering growth stages, wheat should be able to withstand temperatures of 28°F for two\ hours. Figure 1 shows two bleached wheat heads found in a field on May 20 after cool temperatures on May 16.
Bleached Head on Bleached StemFreeze damage at the heading and flowering stages can severely impact wheat yield by causing sterility. To check for sterility (caused by the freezing temperatures in May), now is a good time to look for grain development (wheat kernels). Depending on where flowering was occurring at the time of the freeze, wheat kernels may be absent in the center, top, and/or bottom of the wheat head.
Diseases. Freeze damage should not be confused with diseases that result in bleached, discolored heads. One such disease is head scab and another is take-all. Although symptoms of these diseases are very similar to those caused by freeze damage, the distribution pattern of bleached heads in the field, distribution of bleached spikelets on the head, and the overall health of the plant supporting affected heads are extremely useful for telling these disorders apart. For instance, head scab and freeze damage may causes partial (only a few spikelets or a portion of the head) or complete bleaching of the heads, whereas take-all always results in complete bleaching of the heads. In addition, scab affected heads are often scattered throughout the field, while heads affected by take-all are always found in patches ranging in size from a few heads to huge sections of the field. Freeze damaged heads may or may not be found in patched (low spots in the field), and may be empty and deformed, with distorted awns, whereas head affected by scab and take-all are generally never deformed. Moreover, since talk-all is a rot-rotting disease, affected plants are often shorter, with stems
and leaves that die prematurely (straw-colored) by the time the heads become bleached. Scabby and freeze damaged heads are often found on green, healthy-looking stems that senesce naturally. Read more about other head diseases and disorders at:
http://extensionpublications.unl.edu/assets/pdf/ec1872.pdf