Figure 1. Purple color on corn, due to buildup of anthocyanin caused by cold temperatures.
Figure 1. Purple color on corn, due to buildup of anthocyanin caused by cold temperatures.

The recent rains combined with unusual low temperatures (day/night) this spring are causing slow plant growth for all summer crops, including corn.

Related to the slow growing conditions, today I received a question on the presence of purple coloration in corn seedlings. The first thought that comes to the mind of agronomists and producers is that this could be an indication of “phosphorus deficiency.” Phosphorus deficiency is also generally associated with stunted plants and thin stalks. Other potential causes of purple color can be hybrid-related, a buildup of sugars (sunny days/cold nights), and restricted root growth. Thus, the question is: What is the main factor affecting the plant color if the crop otherwise looks very healthy, uniform, and vigorous?

In recent years, purple coloring on corn seedlings has been documented in different environments under diverse management practices and hybrids. The color is just the expression of a pigment called anthocyanin. The expression of this color is governed by multiple genes, and some of those are more sensitive to low temperatures (40-50 degrees F). Therefore, low night temperatures such as those we have experienced at times over the past couple weeks will promote the purpling color in corn seedlings. Producers do not need to worry about this. As soon as the temperature warms up, the purple color should disappear. If not, then consider taking a soil sample for potential phosphorous deficiency.

At this point, the purple color is simply reflecting a small degree of cold temperature stress -- nothing severe. The plant is growing very slowly, but good growth and development should resume after the temperatures go back to the normal for this time of year.

Will the yield be affected by this stress? Previous information collected by several researchers concluded that yield is not likely to be affected by this phenomenon. Still, it is always good to continue scouting your acres for early identification of any potential problem affecting your crops.