Another batch of very wet weather during the second week of June is not only preventing those who aren't finished from completing planting, it's also affecting the appearance of young corn plants that have emerged recently. Bob Nielsen, a Purdue University agronomist and corn specialist, says it's not likely due to phosphorus deficiency, which used to be the first thing people thought of when they saw purple corn. If it's a true phosphorus deficiency, it may be because of other factors affecting roots and phosphorus uptake.
Nielsen says the process in the plant that produces the purple color is well understood. What triggers it isn't as clear. The purple develops when a reddish-purple pigment, anthocyanin, is produced in the plants. Some hybrids express this more than others. In fact, some hybrids don't even have genes that let them produce this compound.
While one cause is tough to pinpoint, Nielsen says most people agree stresses are involved. When these stresses prevent plants from fully using photosynthates produced during the day, the condition is more likely, providing the hybrid is capable of producing the pigment in the first place.
Cool night temperatures- which have been prevalent- root restrictions, such as by soil compaction, which is also more widespread this spring, and either very wet or very dry soils can all trigger it. In this case, waterlogged soils would be the more likely candidate than drought causing a lack of enough moisture for the plant.
Bright sunny days during the same period as the cool nights, where temperatures fall into the upper 30s or low 40s, for example, actually aggravate the situation. Sugars produced during the day can't be properly handled by the plant at night, when this process typically occurs.
The big question everyone wants to know is if purpling affects yield by the end of the season. Again, Nielsen says it's not a clear-cut answer. "In most cases the purple will disappear as temperatures warm and plants transition into the rapid growth phase," he notes.
"It's the cause of the purpling, not the purpling, that determines if yield will be affected. If it was environmental, ie, sunny days and cool nights, there should be no effect on yield. If restricted roots was the major cause, potential effects on yield depend upon whether the root restriction is temporary or permanent."
Corn plants can recover from temporary restrictions with little or no yield impact, the agronomist adds. However, if roots are stressed for an extended period of time, then plants may become stunted. Yield loss could become real.