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Agronomic Crops Network

Ohio State University Extension


Late season purple corn

Growers are reporting reddish-purple plants in their corn fields and sometimes observing that the degree of purpling varies among hybrids. Several factors can cause purpling of corn plant tissues late in the season. As a defense mechanism to protect photosynthesis, a corn will form pigments to help absorb excess light and divert it away from their photosynthetic centers as a form of sunblock. This purple color is from anthocyanins, which can be formed from excess light or from a buildup of sugar (sucrose). In some cases, like in cool bright conditions early in the season, anthocyanins are important because they help the plant tolerate the bright sunlight and get rid of the extra energy it can’t use for photosynthesis. Diverting the excess sunlight protects the photosynthetic mechanism and can reduce the time needed for the plant to recover from excess light stress. In the cases of purpling during grain fill, the pigmentation is likely to occur when plants cannot utilize all the sugars that the plant is producing. Excess sucrose produced by photosynthesis accumulates in the leaf tissue, husk tissue, parts of the stalk, and triggers formation of the reddish-purple pigment anthocyanin. This can occur in some cases because the silk strength is less than what would normally be expected (barren plants and plants with ears removed prematurely, wildlife damage (especially raccoons), etc.). In years with environmental stress - like the drought this year, plants may have smaller than expected ears or few kernels per ear which can result in prominent purple plants. Disruption of the sugar distribution channels by pests like corn borers can occur when they burrow in stalks and ear shanks. This damage results in a buildup of sugars in the leaves and stalks triggering anthocyanin production and the appearance of purple plants. Purpling is also associated with plants producing "beer can” ears. In this case, these stunted ears with limited numbers of kernels cannot use all the sugars being produced by the plants, so sugars accumulate and plants turn purple. Traces of purpling on plants, which appear healthy, with normal ears, also occur. The extent to which plants turn purple is also influenced by hybrid genetics with some hybrids more inclined to purple than others when some stress disrupts the flow of sugar from leaves and stalks during grain fill.

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.