Dr. Dan Talks Agronomy

The Color Purple

A review of why corn turns purple can help diagnose the problem in fields where the symptom is showing up. (Photo courtesy of Purdue University)

Chances are you grabbed a coat several times this spring when temperatures dipped below normal. If you got chilled through and through, a typical remark might be that you: "turned purple from the cold."

Corn seedlings have their own purpling phenomenon. This week, sightings of purple corn seedlings in Ohio brought questions as to why. Peter Thomison, Ohio State University Extension agronomist, noted that the color change is likely just a cosmetic problem that will go away on its own after several days of 70-degree-Fahrenheit or higher temperatures. (You can read his report at http://bit.ly/…)

However, he also observed that if plants don't change back to their normal color, it is important that growers determine the cause. A nutrient deficiency or some other issue such as reduced root development could be causing the discoloration.

The characteristic reddish to purplish hue on seedling corn leaves is likely due to stress disrupting sugar production within the plant. Cool, wet or compacted soils or shallow planting will temporarily disrupt plant metabolism. The production of anthocyanin pigment is triggered by stress or a combination of stresses. It typically occurs in the early vegetative stage. Some hybrids are more sensitive than others.

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Phosphorus deficiency is another possibility, and using a starter at planting has been one of the solutions. When soils are cold and wet in the spring and seedlings lack roots, there is not enough phosphorus available to meet the needs of the growing seedling. When soils are warmer and drier, organic matter will mineralize enough phosphorus in the spring to meet seedling needs. Phosphorus deficiencies are usually seen on no-till soils that remain cooler after planting. Almost all pop-ups or starter fertilizers contain phosphate because this is considered critical for corn.

Thomison observed another interesting purpling possibility. "If corn follows a fallow season, a root fungus called mycorrhizae reaches a low population. Mycorrhizal infection of corn aids in phosphorus and zinc uptake. Until the fungal growth is stimulated by the corn roots, which exude starches and sugars, the plant may stay purple color for a while," he wrote.

Young corn plants that turn purple should return to a healthy green by the sixth-leaf stage. This happens rapidly if the weather warms up quickly, or it can be slower if the weather remains cool, retarding both root and shoot growth in the seedling.

If new leaves come on green, but leaf tips and margins of the leaves retain their purple color, this is the sign of phosphorus issues. Corn lacking phosphorus will also grow more slowly.

Treatment options to remedy phosphorus deficiency are possible, but keep in mind that phosphorus is immobile in the soil solution. Surface application will limit availability to the top couple inches of soil. Injection as a sidedress treatment will increase availability, but root pruning becomes a concern as corn size increases.

For more information on phosphorus deficiencies go to:

http://bit.ly/…

http://bit.ly/…

Dan Davidson can be reached at AskDrDan@dtn.com

(PS/AG)

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