Causes of wheat stress in western and central Kansas
click image to zoomTom Maxwell, K-State Research and Extension Central KansasStressed wheat on terrace tops in Saline County, May 8, 2012. Wheat is under stress in much of western Kansas south of I-70 and west of Pratt and Great Bend. In areas east of U.S. Highway 281, there are also areas where wheat is under stress, especially on terrace tops.
Stressed wheat is generally showing some combination of the following symptoms:
* White heads, which developed very quickly over a wide area
* Curled and dried up flag leaf
* Tillers that have sloughed
* Loss of one or more small developing kernels in the spikelet
* Poorly developing kernels
* Chlorotic leaves due to poor root development and nutrient deficiencies
click image to zoomJim Shroyer, K-State Research and ExtensionWheat under stress in Barton County, May 8, 2012. This stress is throughout the field. The stress this year came on quickly. There were general rains earlier in the spring, and topsoil moisture was adequate in most areas until recently. But where subsoils were very dry after last summer’s drought, the wheat needed a regular supply of rainfall events this spring to support the topgrowth. Where that didn’t happen, the wheat quickly became stressed, especially during the periods of extreme heat this spring – the latest being May 4-5.
Heading and grain fill is a period of high moisture use, with wheat using about 0.25 to 0.30 inches of moisture per day. If the moisture isn’t available, the wheat will begin to show the symptoms listed above. The combination of dry soils and heat, in particular, will cause heads to turn white rather quickly, almost overnight. Any additional stress, such as diseases or insects, will just add to the stress.
click image to zoomJim Shroyer, K-State Research and ExtensionKernels from the field above. These kernels are in the milk stage, and have stopped developing due to heat and drought stress, and the death of the flag leaves. This will result in reduced yields and low test weight. Cool weather has returned, but the crop still needs another rain or two where it is dry. If rain comes to stressed wheat while the kernels are still in the milk stage of development or earlier, the wheat may be able to recover some yield and test weight potential as long as the flag leaves are still alive. If the plants are under severe stress and shut down while kernels are in the early dough stage, it is unlikely that any subsequent rain will help the kernels complete their fill. This will result in a loss of yield and low test weight regardless of the weather during the remainder of the season.