June 18, 1998 5(13):73
Joe Lauer, Corn Agronomist
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
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
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.