Why do Corn Leaves and Stalks Turn Purple Under Drought Conditions and Can it be Resolved?

Water is essential for corn as it supports key processes like nutrient absorption, photosynthesis, and growth. Corn water use increases as plants grow and gain vegetation, with the highest needs at late vegetative and early reproductive growth stages. Soil water can be released into the atmosphere via evaporation, as well as plant transpiration. Crops consume water from the soil, which moves into the plant via the roots, travelling through the stem and leaves, and returns to the atmosphere through the stomata by transpiration. Adequate plant moisture ensures strong root development, nutrient transportation, and reduction of stress; ultimately boosting yield potential and grain quality. When corn undergoes drought stress conditions, crop response can be variable depending on timing, duration, and severity of the conditions endured. Visual symptomology of drought stress can include wilting or curled leaves during the day, reduced growth of meristematic tissues, and a purple-reddish coloration of otherwise green tissues such as the stem, leaf or husk of the plant.

Leaf curling occurs as the corn plant responds to drought stress by closing the stomates (tiny pores in the epidermis of leaves) to reduce transpiration and conserve water (Figure 1). Keep in mind that the earlier in the day that curling is observed, the greater the stress the plant experiences, leading to a greater impact on final yield potential. Plant growth is reduced under drought conditions including overall plant height, as well as leaf surface area. The reduction in size of these green tissues also reduces the amount of light interception, further limiting photosynthesis. Red-purple coloration in leaves is from a buildup of anthocyanin pigments due to the abundance of sugars in the stalks and leaves that is not being utilized as quickly as they are being produced (Figure 2). Purple coloring can be observed throughout the season, but it is influenced by different stressors. Young plants early in the season may appear purple from underutilization of sugars due to stress from cool night temperatures, a restricted root system, water stress, or lack of phosphorus uptake. Late vegetation and into early reproductive stages, purpling is most likely due to drought stress and the plant’s inability to move sugars to sinks. Once into reproductive stages purple corn can appear when ears are partially or fully barren, as the plant consumes less sugars than it is producing (Figure 2). Other stressors that promote the buildup of sugars in corn include compaction, herbicide injury, insect injury, and disease.

As stated before, overall impacts of drought stress on the crop and final yield potential can vary based on the timing, severity, and duration endured (Table 1). Stand loss and plant death can occur at any time during the season. If plants are showing purple veins, husks, and stalks, very little can be done agronomically to resolve the cause (drought) for the purpling.

Table 1. Estimated Percent of Potential Corn Yield Loss When Corn is Under Drought Stress for Four or More Consecutive Days*

Generally, early vegetative corn is more tolerant of higher temperatures, and drought stress conditions. At this stage the plants are small and have a lower demand for water. Under dry soil conditions, plants generally develop deeper root systems which may be an asset to the plant later in season when water and nutrient demands are higher. As the plant matures through vegetative stages (V6 to V14), photosynthesis is reduced under drought conditions. This reduction occurs when the leaves curl and close the stomates to reduce water loss, limiting the uptake of carbon dioxide. Under these conditions, stunted growth can be observed. Early termination of lower leaves may occur to reposition sugars and nutrients to growing tissues, but nutrient deficiencies can still exist. Reduction in the number of kernel rows, and kernels per row can also occur. Drought stress experienced at silking (R1) up to milk (R3), has even more detrimental impacts on yield potential. Tassel development may hasten, and silking may be delayed leading to reduced or failed pollination. Kernel abortion can also occur leading to reduced yield potential. From dough (R4) to physical maturity (R6) drought conditions can cause the plant to prematurely decline and senesce. Plant health also suffers, increasing the potential for ear and stalk rots. Thus, reducing grain quality and hygiene if being fed to cattle. For additional information on crop response and yield effects of drought stress, please see the Purdue University publication Corn Responses to Drought Stress by Dr. R.L. Nielsen.

In summary, plant water status throughout the growing season is one of the most influential components to corn production. Crop impact to final yield potential can be drawn based on these factors. Despite the many plant processes impacted by drought stress, corn is very resilient, and plant recovery can be considerable if soil moisture is improved at the right time. However, if corn veins and stalks are turning purple, it is likely too late for any moisture to reduce the purpling.

Channel Agronomist
Ashley Madson

Sources

¹Licht, M, and Archontoulis, S. 2017. Influence of drought on corn and soybean. Integrated Crop Management. ICM News. Iowa State University Extension and Outreach. https://crops.extension.iastate.edu/cropnews/2017/07/influence-drought-corn-and-soybean

Ciampitti, I. and Shoup, D., 2017. Late-season purpling in corn. Agronomy eUpdates, Kansas State University. https://eupdate.agronomy.ksu.edu/article_new/late-season-purpling-in-corn-650-4

Nielsen, R.L. 2023. Corn responses to drought stress. Corny News Network, Purdue University Agronomy Extension. https://www.agry.purdue.edu/ext/corn/news/timeless/CornRespDrought.html

Nielsen, R.L. 2009. Reddish-purple corn plants late in the season. Corny News Network, Purdue University Agronomy Extension. https://www.agry.purdue.edu/ext/corn/news/timeless/PurpleCorn2.html

Quinn, D. 2022. Heat stress and drought consideration for corn. Pest & Crop Newsletter, Extension Entomology. Purdue University. https://extension.entm.purdue.edu/newsletters/pestandcrop/article/heat-stress-and-drought-considerations-for-corn/

Classen, M.M. and Shaw, R.H. 1970. Water deficit effect on corn. II. Grain components. Agronomy Journal. 62:652.

Rhoads, F.M. and Bennett, J.M. 1990. Corn. In Stewart, B.A. and Nielsen, D.R. (editors). Irrigation of agricultural crops. p. 569 – 596. ASA-CSSA-SSSA, Madison, WI.

Shaw, R.H. 1988. Climate requirement. In Sprague, G.F. and Dudley, J.W. (editors). Corn and corn improvement. p. 609-638. ASA-CSSA-SSSA, Madison, WI.

Web sources verified 3/24/25. 1110_544362