Purple corn syndrome: What causes purple coloration of corn?

Early season stress and restricted root growth are likely contributors to early season purple coloration of corn.

Purple coloration to corn leaves.

Purple coloration to corn leaves.

It is not unusual to have some corn producers call the Michigan State University Extension office to express concern about purplish coloration this time of year. There are several factors that contribute to early season purple coloration, but the major factors are likely to be early season stress and restricted root growth. Corn leaves produce sugars by photosynthesis. These sugars are ordinarily metabolized to generate energy for further shoot and root growth and development. However, when growth slows down – for example, when temperatures get too cold – the sugars tend to accumulate in the leaf. This triggers anthocyanin pigment formation and causing the purplish color (see photo).

Restricted root growth induced by compacted soils and compacted furrow side-walls is also closely associated with purpling of corn. On some fields, the purplish color is more visible in field headlands and in spots within fields and wheel tracks. Sometimes the phosphorus (P) deficiency also causes purple coloration, but early season P deficiencies may be related to the restricted root growth. Soil test levels should determine P sufficiency in the soil. If sufficient P is present, adding more phosphorus will not turn purple leaves green.  

Research on understanding purple corn has shown the anthocyanin pigment is produced only on the surface layer of cells and does not affect the chlorophyll content in the leaf. Therefore, early season purple coloration does not generally impact corn yield. Furthermore, there are some genetic differences in the predisposition of corn hybrids to purple coloration.

Young corn plants that turn purple usually grow out of the symptoms after about the six-leaf stage. When the weather warms up and rapid growth resumes, sugars are metabolized normally and plants attain their normal green color. If the problem persists, then some remedial measures such as soil testing and tillage practices are needed.

Michigan State University Extension recommends farmers scout early season corn fields for compacted soil, nutrient deficiency symptoms, pesticide misapplications, root injury or deformities, irregular planting depth and emergence. Some remedial actions such as tillage, equipment calibration and soil testing can be implemented this fall or early spring. 

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