Greg Roth
Associate Professor
Penn State
January, 2003

Background

     During late May, we visited this Lancaster County corn field that exhibited a severe case of erratic and late emerging corn. Corn had emerged on one side of the field quite well, but in another area, emergence was delayed about 3 weeks. In some areas, where some corn had emerged early, there was variation in emergence within the row. (Click on the image to the right for a larger view)

Diagnosis

     We dug up both early and late emerging corn plants to assess the situation. On most of the corn in this field, we found that the planting depth was one inch or less. Even the early emerging corn plants did not have a mesocotyl between the seed and the primary root system. Where we dug up adjacent plants in the row that emerged at different dates, we found that the early emerging plants were planted slightly deeper. Normally the mesocotyl should be about 0.75 inches long on corn that was planted 1.5 inches deep. (Click on the image to the right for a larger view)

     We also dug up plants in adjacent fields that were planted with a different planter in a similar time frame as this field. The planting depth in these fields was approximately 1.5 inches. While these fields showed some variation in emergence, it was not nearly as severe.

     Ideally corn should be planted 1.5 inches deep in most situations. In this field, the dry early spring conditions and tillage caused soil moisture levels to be reduced to the point where much of the seed did not germinate until the next rainfall which occurred in mid May. This variation in emergence can reduce yield by 5-10%. Many of the late emerging plants that were mixed in the row with other plants in this field did not pollinate very well.

     Shallow planted corn can also be subject to herbicide injury in wet springs, especially where Prowl, Python or Hornet was applied and planting is followed by cool wet conditions.

     Shallow planting is a common problem in Pennsylvania corn fields. Planting depth should be monitored carefully in each field or at least where soil and tillage conditions change. Erratic planting depth usually indicates a planter problem.