Some of the chatter down at the Cock ‘n Bull Cafe still centers on the many fields of corn that exhibited such intense purpling several weeks ago. Most of the purple color has disappeared from those fields, but in many affected fields the plants in those areas remain visibly shorter and lighter green in color than the areas that did not purple. Growers are naturally concerned and asking questions about the eventual yield effect from the purpling.
As I indicated earlier in what has become an annual article about purple corn (Nielsen, 2012), it’s not the purpling itself that you should be concerned with. The purpling is simply a “red flag” that something is going on in the field, something that is stressing root development.
If the “something” that is stressing root development or function is a minor stress and short-term in duration, then there will likely be no effect on yield potential at harvest. The classic example of such a minor stress factor is the combination of brilliant sunny days (a lot of photosynthesis) coupled with cooler than optimum nights (reduced utilization of photosynthate). This combination results in the classic, and predictable, purpling of hybrids with the purpling genetics (Nielsen, 2012) and will disappear once temperatures rise to consistently warm levels.
If the “something” that is stressing root development or function is a more serious or lengthy stress, then indeed the affected areas will likely remain stunted and will likely result in lower grain yields. Such serious stress factors include lengthy periods of saturated soils, soil compaction, planter furrow compaction, herbicide injury, nematode injury, starter fertilizer injury, and low soil pH.
So, purpling in young corn fields is simply a “red flag” that should encourage growers to further investigate the nature of the stress(es) that is restricting root development or function. That diagnosis will help you determine whether to expect yield loss in areas of fields that turn purple early in the season.
Also, please recognize that hybrids without the purpling genetics (Nielsen, 2012) are usually just as easily affected by the stress factors that limit root development or function. The difference is that those hybrids do not (cannot) turn purple and so the initial effects of the root stress are not as evident from the road.