Appropriate Timing for Optimizing Corn Yield Response

Interest in mid-season application of various inputs has certainly increased as we try to improve corn productivity through better management, different strategies and alternative products.  This naturally creates questions regarding the appropriate application timing to optimize crop response to various inputs, including nitrogen, foliar fertilizers, fungicides, many other products intended to promote “plant health” or alleviate crop stress, as well as irrigation (particularly limited irrigation).  Corn’s physiology is a primary factor determining how responsive the crop is to these factors.  Other principles to consider are discussed in this excellent article regarding soybeans:  https://www.mississippi-crops.com/2012/06/16/soybeans-should-i-add-that-insecticide-with-the-fungincide/

Corn physiological sensitivity to deficiencies, stress or photosynthetic capability definitely varies with growth stage.  Early reproductive growth stages, such as tassel (VT) or sik (R1) are the most sensitive to limitations and plant tolerance generally increases as plants mature.  Issues at any stage may limit yield until physiological maturity occurs.  Reproductive stages are also generally more sensitive than vegetative stages.

Does this mean tassel stage is the best timing for various inputs?  Not necessarily, it depends on the crop condition relative to whatever factor you are attempting to influence.  This must be evaluated by field scouting and other means to identify a limitation capable of reducing productivity.  If you identify a problem that you can control, yes, it is critical to correct it ASAP in order to limit permanent yield loss, if it threatens economic loss.  However, if there are no limitations present, you are not likely going to generate any crop response to various inputs.  For example, if crop health is good prior to tassel and best management practices were employed, there is little or no reason for the crop to respond to supplemental nitrogen application at a specific (pre-tassel) growth stage, unless substantial nitrogen loss occurred during the season or a sub-optimal amount was originally applied.  Likewise, our and other Universities’ research shows automatic fungicide application is not going to improve corn yield or other plant attributes in the absence of foliar disease.

Returning to the nitrogen management example, if you suspect some nitrogen loss occurred during the season due to adverse environmental conditions, this may warrant supplemental fertilizer.  If this crop is at a pre-tassel stage, currently healthy and shows no signs of deficiency, supplemental nitrogen timing should not be particularly critical, as long as it is available for plant use before it becomes limiting late in the season.  In other words, in this scenario, it is not necessary to sweat whether you apply supplemental nitrogen at V15, tassel or brown silk.

Rather than focusing efforts at a “magic growth stage,” or shutting down at early dent, it is more important to let the crop dictate what it needs and when.  Realize corn yield reduction resulting from limitations gradually declines as the crop approaches maturity, but continues to occur all the way to physiological maturity.  The primary difference is that corn grain yield is not as vulnerable to stress as the crop approaches maturity.  If you need help assessing the degree of response likely from specific issues and timing, feel free to contact me or our other crops team specialists for assistance.