I have been receiving calls about what the cool night temperatures we have recently been experiencing might do to corn grain yields. Most farmers believe that corn grows best when the nights are hot. The reverse is true. Corn uses more energy in cell respiration on warm nights resulting in lower yields. In a field study at Urbana, IL, (Peters et al., 1971), heating corn in closed chambers with electric heaters reduced yield by 40% compared to natural and cooled air using air conditioners (Table 1).

Table 1. Effect of night temperatures during 52 nights following pollination on corn yield during 1969 at Urbana, IL.
Treatment	Average Night Temperature (oF)	Grain Yield (bu/A)
Natural Air (Control)	65	168
Cooled	62	162
Heated	85	100
derived from Peters et al. (1971)

Leaf temperatures are influenced by the sky condition. On a clear night, the leaf radiates heat into outer space at a rapid rate and cools quickly. This is observed when heavy dew forms early on leaves at night. When clouds are present, the leaf temperature is the temperature of the cloud cover, which is always warmer than outer space and dew forms later if at all. Very high humidity has much the same effect as a cloud cover. In essence, the kind of night when you feel the greatest need for an air conditioner is a poor night for corn growth. High yields in the Corn Belt are made in spite of, not because of, warm humid nights. The ideal situation is cool nights, sunny days and moderate temperatures (Aldrich et al., 1986).

Another observation that seems to coincide with cool nights is a greater incidence of silk balling. There is little research to document the environmental conditions that cause this problem, but the consequence is poor pollination and grain set. Unfortunately, there is nothing you can do to manage this problem.

Literature Cited

Aldrich, S. R., W. O. Scott, and R. G. Hoeft. 1986. Modern Corn Production. A&L Publications, Inc., Champaign, IL.

Peters, D. B., J. W. Pendleton, R. H. Hageman, and C. M. Brown. 1971. Effect of night air temperatures on grain yield of corn, wheat, and soybeans. Agron. J. 63:809.