Cool start to growing season affects corn
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
The cool, early May temperatures have resulted in significant variability in corn emergence across fields. Ideally, we would like to see all corn plants emerge simultaneously to minimize plant to plant competitive advantages and maximize yield potential. Under marginal conditions of cool weather within field spatial variability conditions are exacerbated. Areas with darker soils and more well drained soils warm up quicker and, conversely, poorly drained areas and areas with heavy residue take longer to warm up. The large disparity in soil temperatures drives the disparity in corn seedling emergence. Additionally, if the cool temperatures continue, we will likely see symptoms of yellow and purple corn. The pale yellow color is symptomatic of low photosynthetic activity and general nutrient stress experienced by the plant. Similarly, poor root growth can result in purple-colored corn.
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. These same conditions can also result in purple-colored corn. The restricted root growth resulting from the saturated soils can cause a build up of sugars in the corn leaf. These sugars would normally be used for root growth, but when accumulated in the leaf, result in the production of anthocyanins, which give the leaf a purple color. In addition, some corn varieties have inherently higher levels of anthocyanins. If the purple color persists after field moisture conditions normalize, the discoloring may be indicative of other root related problems such as a compaction problem or a phosphorus deficiency in the soil.
Cool wet soils and weakened plants also set the stage for fungal and bacterial root disease in corn. 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.
The good news is that corn will generally overcome these early season stresses with a good dose of warmer weather. Continue to monitor nutrient levels, particularly nitrogen. Once the weather turns, most of the corn will likely outgrow early season discoloration symptoms.