Injury symptoms from the April 14th freeze are now showing in the Oklahoma wheat crop. Robert Calhoun and Matt Knori madeTh a trip through north central Oklahoma yesterday splitting stems (some pictures are posted below). Their first stop was our wheat variety trials at Marshall Oklahoma where they found 20% injury in our grazed wheat plots and 51% injury in our non-grazed wheat plots. While planting date and management system clearly affected the level of injury, variety did not seem to have much effect.
Next stop was a grazed field north of Hennessy where they found little injury. The same was true for a field in the Waukomis area and the Lahoma variety trial where they found less than 5% injury. Not too far to the north, however, our Lamont variety trial sustained over 80% injury. I received similar reports of severe wheat freeze injury from Curtis Vap in the Blackwell area.
Late last week our team traveled to Apache to apply fungicides to the wheat variety trial, but never unloaded the sprayer. Freeze injury was severe and clearly visible without splitting stems. Our wheat at the Chickasha research station had little to no damage, and most wheat in the area seemed to dodge the freeze bullet. I will make a bigger loop into southwest Oklahoma later this week and report findings.
Injury symptoms should now be easily identifiable and growers can assess damage to individual fields. I recommend splitting 10 stems at four or five locations throughout the field and determining % injury from these numbers. If injury is extremely variable, increase sample size. While it is fairly easy to determine the extent of injury on individual fields, the hit or miss nature of freeze injury this year makes it difficult to estimate the total impact on the Oklahoma wheat crop as a whole.
The drought has severely limited resilience in our crop and we are entering late April, so I do not anticipate there will be much of a recovery or rebound in fields that were severely damaged. It is important to note that 50% injury does not necessarily mean 50% yield loss. In most cases the actual yield loss will be less than the % injury. So, it is reasonable to expect that 50% injury might only result in a 35 or 40% yield loss. Of course, this depends on several factors such as soil moisture and temperature.
Finally, a word on foliar disease and fungicide application. I would make decisions regarding fungicide application based on variety, current disease reports, and the yield potential of the crop as it stands right now. Our long-term data shows that fungicides protect yield potential to the tune of about 10%. Of course individual variety responses can deviate from this number but 10% is a good rule of thumb. I do not, however, recommend applying a fungicide to “assist the crop in recovery from freeze”. Again, make these decisions based on the remaining yield potential rather than an effort to attempt to nurse the crop back to health after freeze.