By R.L. (Bob) Nielsen
Agronomy Dept., Purdue Univ.

Like the swallows that return to Capistrano, it seems that purpling in young corn returns every year somewhere in Indiana. Today I spotted some young corn plants (V3 to V4) with leaves that were noticeably purplish-red. The purplish plants were more prevalent in the wetter areas of the field and almost non-existent in the drier areas. While mildly attractive from an ornamental standpoint, landlords and tenants alike often become concerned when they see their fields take on a purplish hue that is clearly evident from the window of the pickup at 60 mph.

Purpling of corn plant tissue results from the formation of a reddish-purple anthocyanin pigments that occur in the form of water-soluble cyanidin glucosides or pelargonidin glucosides (Kim, 1998).  A hybrid's genetic makeup greatly determines whether corn plants are able to produce anthocyanin.  A hybrid may have none, one, or many genes that can trigger production of anthocyanin.  Purpling can also appear in the silks, anthers and even coleoptile tips of a corn plant.

Well, you may say, that's fine but what triggers the production of the anthocyanin in young corn at this time of year? The answer is not clearly understood, but most agree that these pigments develop in young plants in direct response to a number of stresses that limit the plants' ability to fully utilize the photosynthates produced during the day. These stresses include cool night temperatures, root restrictions, and water stress (both waterlogged and droughty conditions).

There's no question that many corn fields throughout the state have suffered through wet soil conditions during the past several weeks. Soil compaction (tillage- or planter-related) can also restrict the development of the initial root systems. The additional stresses imposed by quite a few relatively cool nights (upper 30's to low 40's) and the occasional bright sunny days (high levels of visible and UV radiation) may be the final "triggers" that result in fields of pretty purple plants.

Since the anthocyanin occurs in the form of a sugar-containing glucoside, the availability of high concentrations of sugar in the leaves (photosynthesis during bright, sunny days) further encourages the pigment formation. If fields are stressed by other factors such as soil compaction, herbicide injury, disease damage, or insect injury, the purpling becomes even more pronounced.

It has been my experience that the combination of bright, sunny days and cool nights when corn ranges from V3 to V6 in development (3- to 6-leaf collar stages) most commonly results in plant purpling.  Hybrids with more anthocyanin-producing genes will purple more greatly than those with fewer "purpling" genes.  In most cases, the purpling will slowly disappear as temperatures warm and the plants transition into the rapid growth phase (post-V6).

I have rarely diagnosed phosphorus deficiency as the primary cause of purple plants early in the season. Nonetheless, cold or wet soils inhibit root development and can aggravate a true phosphorus deficiency situation, frequently causing even more intense leaf purpling.

What About Yield Losses? Does the leaf purpling lead to yield losses later on?

The cause of leaf purpling, not the purpling itself, will determine whether yield loss will occur by harvest time.

If the main cause is the combination of bright, sunny days and cool nights, then the purpling will disappear as the plants develop further with no effects on yield. If the stress of restricted root systems is a major contributor to the purpling, then the potential effects on yield depend on whether the root restriction is temporary (e.g., cool temperatures & wet soils) or more protracted (e.g., soil compaction, herbicide injury). Plants can recover from temporary root restrictions with little to no effect on yield.  If the root stress lingers longer, the purpling may continue for some time and some yield loss may result if the plants become stunted. 

See photos here.

SOURCE: Purdue University.