The Tassel Shot: What is the Best Timing?

Interest in mid-season application of various inputs is certainly increasing as we try to improve efficiency and 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, 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, but issues at any stage may limit yield until physiological maturity occurs. Does this mean tassel stage is the best timing for various inputs?  Not necessarily, you also have to assess the crop condition.  This is best evaluated by field scouting or other means capable of identifying good crop health, or conversely limitations capable of reducing productivity.  If crop health is good prior to tassel (no nutrient deficiency or disease present), you wouldn’t expect the crop to be responsive to management timing at that specific growth stage. For example, ours and other Universities’ research shows 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 much higher likelihood of generating a profitable response.

The topic generating the most discussion this season is supplemental nitrogen application near tassel. More growers likely plan a pre-tassel N application as a part of their standard program, but we have also experienced more nitrogen loss than recent years because of the persistent rain and saturated soils this spring. For more information about calculating N loss, refer to: https://www.mississippi-crops.com/2013/05/14/how-to-estimate-nitrogen-loss-resulting-from-saturated-soils/

So what is the appropriate timing for the â€œtassel shot” of N? Early season nitrogen loss may have some effect, but I will boil it down to two different scenarios. If your crop is currently dark green and healthy (where compaction and other by-products of wet conditions have not stunted plant growth) 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 late 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 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 warrant. You would like to incorporate the nitrogen into the soil ASAP, so that plants can pick it up and improve plant health well prior to the critical pollination time.

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 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 normally not quite 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 any of our crops team or myself for further assistance.