Why is this corn purple?

Over the past couple of weeks, I’ve seen or have heard about several fields where the corn leaves have turned purple.  This purple pigment is due to over-accumulation of sugars in the leaves. Sugars are building up in the leaves because not enough of them are being transferred to the plant roots which can be caused by a number of things.  The most common answer is that the problem is caused by a phosphorus deficiency. Low phosphorus inhibits sugar movement from the leaves to the roots but due to the amount of livestock in our area, phosphorus deficient soils aren’t that common so the purple color probably has other causes.  Weather patterns play a role in root development. Cool temperatures and excessively wet or dry conditions reduce root growth and root mass for sugar translocation.  Late planting and hot temperatures generally lead to faster vegetative growth compared to root growth in young corn plants.  Soil compaction and low pH will reduce root growth and phosphorous availability. Plant genetics can dictate how much certain hybrids will produce purple pigment.

The question everyone would like answered is how will this affect yield.  If the problem is a hybrid that readily expressed the pigment or weather related, then the plants will probably grow out of the color with little yield impact. If the problem is due to soil compaction, low phosphorous, or low pH then decreased yield would not be surprising. There are methods available to test for these last three situations if you’re interested.  Contact WS Ag Center for plant tissue, soil, and soil compaction testing.

Mark Kendall


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