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What Causes Purple Coloration of Corn?

It’s normal to have some corn producers express concern about purplish coloration of corn 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. 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.

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.

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.

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.

Source: George Silva, Michigan State University

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