Weather causing cold stress on newly planted corn
By Noel Mues
UNL Extension Educator
Recent rains have helped but we are still in the grip of continuing drought and much of western Nebraska has severely depleted subsoil moisture levels. In addition, the unusual spring has caused recent temperature swings. This and cold soil temperatures are causing planting delays and stress on recently planted crops.
The early season seedbed can be an inhospitable environment for corn seeds and seedlings. As planting dates have moved earlier, the potential for cold, wet conditions after planting has increased. When unfavorable weather persists in the spring, planted corn may be exposed to cold, saturated soil conditions for three weeks or longer before emerging.
Two recent trends, early planting and reduced tillage, have introduced early season cold stress into areas not usually affected by this problem. Even in southern and western regions of the U.S., corn grown in these production systems can experience similar stress levels to those of colder northern regions. Although there are many advantages to reduced tillage, the level of early season stress has increased along with its adoption. This is due primarily to lower soil temperatures, water retained in crop residue, and slower seedbed drying. Corn grown under irrigation can also experience significant stress if the irrigation water is sufficiently cold.
DuPont Pioneer and other companies have conducted stress emergence ratings to help categorize corn hybrids for their genetic potential to emerge under stressful environmental conditions (including cold, wet soils or short periods of severe low temperatures).
One of the less understood effects of chilling injury to newly planted corn is what is called “imbibitional chilling.” Injury occurring to corn seed that has just been planted, and started to swell, or imbibe water, during the early process of germination; usually occurring within 24 to 36 hours after planting.
While there is some debate over what temperatures cause imbibitional chilling and the time factor associated with the response, there is undoubtedly a response from corn plants that imbibe cold water in the first 24 to 48 hours after planting. With the recent cold weather and some growers planting fields to “beat” the rain, some corn fields may experience symptoms from imbibitional chilling.
It is generally recommended that soil temperatures be 50 to 55 degrees F at planting to avoid this damage. Some reports have even suggested that corn will not be injured if the soil temperature is above 41 degrees F, but there is certainly some risk that the early planted corn may be injured. The soil temperature measured at North Platte at 8:30 a.m. May 1 was 42 degrees F.
Like rubber and other elastic materials, the cells of the corn kernel will expand as the water is imbibed. When the water is cold, the cells will become brittle and are more likely to rupture. If the plant cells do rupture, the new seedling will fail to develop properly. When this happens, we are likely to see delayed emergence, inconsistent plant spacing, and/or “corkscrewing” cotyledons, including leafing out underground.
With modern hybrids, there is likely less risk of this happening because the seed and seedlings are more vigorous, but if you have early planted corn in the ground this year, it will be important to scout it early. Poor stands may need to be replanted.
For additional information see results from DuPont Pioneer’s 2012 research on Stress Emergence in Corn at https://www.pioneer.com/home/site/us/agronomy/research-summaries/stress-emergence-corn.