The following newsletter is from Professional Seed Research, Inc.

The president of this company is Dr. Jim Dodd and some of you may remember me referrencing him as well as this company doing the majority of disease testing of our hybrids.

This letter was his latest posting about the current status of this year’s corn and the effect of the cool temps during the first part of the growing season and how this effect may influence black layer.

Corn Maturity (posted July 2008)

Late spring and early summer of 2008 featured lots of rain and cooler than normal temperatures. Not only did this result in delayed planting but also will cause a late pollination and harvest.

Corn originated in Central America, a semitropical environment that had year around sunlight from about 11-13 hours per day. As the new crop was dispersed into more temperate hemispheres it would pollinate too late for the corn to mature. Fortunately, over a few thousand years, there were humans adept enough to select for the few variants that responded to heat instead of length of day in determining flowering time in corn. Because of the genetic variability, and the ingenuity of our species, corn was adapted to northern Canada by the time the Europeans arrived in North America.

Adaptation to the longer day summers of the temperate zones required a different mechanism for determining maturity. The change was possible because the major factor influencing time to flowering and pollination became accumulated heat, independent of the length of day.

At some time in the growth of a young corn plant, the apical meristem (growing point) cells quit producing more leaves and switches to producing tassel cells. Although this meristem is only a few inches above the soil surface, the change is visible with a microscope. Many years ago, I compared the heat unit accumulation to that point of apical meristem differentiation with all the hybrids of a major U.S. company. All plants were from a single location in northern Illinois with the same planting date. There was a perfect correlation between the heat units to tassel differentiation in the meristem and the published maturity of the corn hybrids. In other words, the main differences in maturity were determined by the heat units needed to cause the growing point to switch from producing leaves to tassels.

The time between differentiation and pollen shedding is mostly independent of heat; it is mostly a time factor. The next phase, the time from pollination to formation of black layer is about 55 days for all hybrids. This means that the biggest variable in determining the time from planting to black layer is the heat accumulation during the first 30-50 days of the season. Cool late May and early June delayed pollination to the latter part of July and early August for much of the Corn Belt. Black layer will not be here until Sept. 15-30. That determines safety from frost. Other genetic factors such as husk thickness, numbers and opening, grain features, cob thickness and environmental factors such as humidity, wind, and heat affect the actual acceptable time to harvest. Except for these drying factors, the corn maturity timing for 2008 is set.

Tex Young, CCA
Sales Agronomist
Great Lakes Hybrids