Cold Temperature Effects on Corn
Cold temperature stress adversely affects the growth of young seedlings and probably predisposes the plants to invasion by soil fungi capable of causing seed rot and seedling blight. In addition to slowing the germination process, cold temperatures, especially if accompanied by precipitation (snow and freezing rain), may cause irreparable harm to the delicate structures of emerging corn seedlings. Restricted root growth resulting from cold soils can cause a buildup of sugars in the corn leaf. These sugars would normally be used for root and shoot growth but, when accumulated in the leaf, result in the production of anthocyanins, which give the leaf a purple color. If the purple color persists after field conditions normalize, the discoloring may be indicative of other root related problems such as a compaction problem or phosphorus deficiency in the soil. In addition, some corn varieties are genetically predisposed to have inherently higher levels of anthocyanins. These varietal differences are readily apparent when viewing variety trial plots this time of year, however, they do not appear to affect final grain yield.
The good news is that corn will generally overcome early season purpling with a dose of warmer weather. Continue to monitor nutrient levels, particularly nitrogen. Once the weather turns, the corn should outgrow these discoloration symptoms. Many factors contribute to the symptom of yellow corn seedlings. Sunlight drives the photosynthetic process and a lack of heat units results in slow seedling growth. Cool spring temperatures combined with saturated soil also limit corn seedling root growth and penetration into the soil. This confounds the slow growth of the corn plant by limiting nutrient uptake. Furthermore, the mineralization and plant availability of nutrients, including nitrogen and sulfur, is slowed down due to slower microbial activity in cool wet soils.
Weather-stressed corn is more susceptible to herbicide injury, which can also result in yellowing. Finally, weakened plants are more susceptible to damage from insects. Scouting for disease and insect pests is especially important in weather-stressed fields of corn.
Freezing Temperature Effects on Corn
Temperatures at or below freezing will kill plant tissue but not necessarily the entire plant.Check low-lying areas of fields where natural “air drainage” is restricted for frost damage first. To assess seedling viability, split a plant lengthwise through the stem. The growing point should be relatively firm and white or cream colored. Darkening or softening of the growing point indicates a nonviable (dead) plant. Replanting may be warranted if these areas are extensive. Seedlings that have not emerged are somewhat protected by the soil and may be protected from frost except at extremely cold temperatures.
The emergence and growth of young corn seedlings is temperature dependent and slows down considerably with cool temperatures. Planting too early increases the vulnerability of corn by slowing down the germination process and lengthening the vulnerable preemergence period. Additionally, very early planted corn has a greater likelihood of being exposed to frost and cold temperature damage after emergence. Corn can survive frost if the duration and severity of the frost is not severe. The growing point of corn remains below the soil surface until the plant is approximately at the V6 growth stage, which can keep the plant viable even though the aboveground plant tissue may be killed. In these conditions, yield may be compromised somewhat by delaying the growth and development of the plant.
For more information on this and other topics related to corn production, contact your state extension corn specialist or your local extension educator/agent.
Here is the link to the corn extension specialists: state extension corn specialist.