This spring there have been numerous reports of yellow corn. Agronomists from southern Minnesota, northern Iowa and western Wisconsin have observed plants with yellowing leaves similar to nitrogen and sulfur deficiency symptoms. In some cases there were root lesions and some death of root tips. On a field basis, plants seemed to be affected throughout the field. Often field streaking of affected plants was observed. Hybrid differences were noted, and it appeared that herbicides might be aggravating the problem.

It is not really clear why there is such a widespread problem. Below are some possible causes, but it is only conjecture and does not have any supporting data.

Since the symptoms were so widespread across numerous soil conditions and management practices, it seems to point to an environmental problem. A unique characteristic of 1998 was the ideal planting season in this region. Corn was planted relatively early, and plants had very good early leaf growth. In fact, leaf growth may have been too good for the root system on the plant. During the early stages of corn development and up until V2, the dominant root systems on the plant are the radical and seminal root systems. Beginning about V2, these seminal roots cease growth and the nodal root system appears, eventually becoming the dominant root system of the corn plant by V5 to V7. These roots grow horizontally 2 to 3 feet and downward 5 to 7 feet. During the transition phase between development of root systems (between V3 and V4), unseasonably warm weather favored leaf growth. The seminal root system may have not been able to keep up with the leaf nutrient demand and temporary deficiency symptoms resulted.

We may also have to blame El Nino! Because we had such a mild winter, we did not get the freeze-thaw action that normally occurs between production seasons. The combine and truck wheel traffic from last fall's harvest that would usually cause some compaction was not broken-up during normal freeze-thaw cycles causing the streaking nature of the symptoms in the field.

We probably will never truly know what caused the yellowing of corn during 1998. Whatever the reason, the yellow corn symptoms are disappearing in the fields I have been watching. The symptoms seem to be temporary and disappear by about V5 to V7 when the nodal root system is dominant and aggressively growing into the soil profile. I would expect minimal impact on yield.