Purple Plants A Problem?

Are you seeing young corn plants in your area turn purple, leaving your growers perplexed? Purdue University’s own headline puts it best: “Prevalent Purple Plants Possibly Puzzle Producers.” The purpling may disappear or point to deeper problems.

All hybrids have the ability to form reddish-purple anthocyanin pigments in varying degrees, which can also appear in the silks, anthers, and even coleoptile tips of a corn plant. Although the answer isn’t completely clear, most experts agree that these pigments develop in young plants in direct response to a number of stresses — including cool night temperatures, root restrictions, and too much/too little water — that limit the plant’s ability to fully utilize the photosynthates produced during the day.

Other stresses, which have been more prevalent this year in states like Indiana, are soil compaction and relatively cool nights combined with bright sunny days may be the final “triggers” that result in fields of pretty purple plants, according to Bob Nielsen, Purdue University Extension corn specialist. Herbicide injury, disease damage, or insect injury causes more pronounced purpling.

“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,” says Nielsen. “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,” he says. “Nonetheless, cold or wet soils inhibit root development and can aggravate a true phosphorus deficiency situation, frequently causing even more intense leaf purpling.”

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, according to Nielsen.

• 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 a 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.

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