The Tassel Shot: When is the Best Time?

Interest in mid-season application of various inputs is certainly increasing as we try to improve management efficiency and corn productivity through better management, different strategies and alternative products.  Improved efficiency resulting from better timing may also reduce expenses and increase profitability. This naturally creates questions regarding the appropriate application timing to optimize crop response to various inputs, including nitrogen, foliar fertilizers, fungicides, or other products. Corn’s physiology is a primary factor determining how responsive the crop may be to most of these factors.

Corn physiological sensitivity to deficiencies, stress and photosynthetic capability definitely varies with growth stage. Early reproductive growth stages, such as tassel (VT) or silk (R1) are the most sensitive to limitations, and plant tolerance generally increases as plants mature.  Reproductive stages are also generally more sensitive than vegetative stages. Does this mean tassel stage is the best timing for various inputs?  Not necessarily, if crop health is good and there are no limitations threatening, you wouldn’t expect the crop to be responsive to management timing at that specific growth stage. For example, ours and other Universities’ research overwhelmingly show automatic fungicide application at tassel stage is rarely going to improve corn yield or other plant attributes in the absence of foliar disease.  This doesn’t mean that fungicide application has no value for corn production. Our recommendation is to use routine field scouting to monitor the corn crop for threatening disease, and better justify fungicide use when there is a reasonable opportunity of generating a profitable response.

The topic generating the most discussion this season is supplemental nitrogen application near tassel. So what is the appropriate timing for the “tassel shot” of N? Nitrogen loss resulting from abundant spring rainfall and saturated soils will likely affect the outcome, but I will boil it down to two different scenarios. If your crop is currently dark green and healthy as it nears tassel stage, supplemental nitrogen timing should not be particularly critical, as long as it is available for plant use before it becomes limiting later in the season.  In other words, in this scenario, it is not necessary to sweat whether you apply supplemental nitrogen at V12, V15, tassel or even brown silk. On the other hand, if inclimate weather has delayed or restricted normal nitrogen application, or your crop shows signs of nitrogen deficiency (yellowing of lower leaves starting at the tips and progressing down the midrib in an inverted “V” pattern), it is critical to apply the nitrogen as soon as conditions allow. Since the fertilizer will not be available to the crop until it is incorporated, it is best to time nitrogen application prior to forecast rainfall or over-head irrigation and well prior to the critical pollination time. However, realize that supplemental nitrogen will not overcome stunting caused by flooding, soil saturation or soil compaction.

Rather than focusing efforts at the”magic growth stage,” it is normally much more important to let the crop dictate what it needs and when.  Realize corn is  generally less vulnerable to stress as the crop approaches maturity, but yield reduction may occur all the way to physiological maturity.  If you need help assessing the degree of response likely from specific issues and timing, feel free to contact any of our crops team or myself for further assistance.