Carefully consider economic thresholds of damage before treating and definitely consider if timing is appropriate to give control by spraying. Watch corn for aphids this year, as number have been large in other crops in many areas. Armyworms have also made an appearance in locations. Corn borer numbers appear down this year, but more time is needed to determine if the recent surge in moth flights will result in any larvae that are detrimental. Many other insects can contribute to problems in corn.
Nutrient deficiencies are very difficult to diagnose.
Soil and plant analysis can help in identification and determination of the cause of these problems. Scout your corn fields regularly in order to eliminate worry about the crop. Check various regions of individual fields so that you periodically see most of each field.