Do cool temperatures hurt corn plants?
Stress from cold temperatures 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 at certain times of the 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 are slowed down due to slower microbial activity in cool, wet soils. In addition, 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.