Corn was planted late and the cool and cloudy days are slowing development in Kentucky and parts of the Midwest. Most corn hybrids in Kentucky need about 2,700 to about 3,300 GDD’s or heat units to reach black layer (physiological maturity). Looking at the GDD calculator on the UK Ag Weather Center, corn planted April 15, 2013 in Mayfield, Kentucky won’t get to 3,000 GDD’s until Sept. 1. Corn planted April 15 in Henderson will get to 3,000 on Sept. 3. Corn planted May 15 in Lexington will get to 3,000 GDD’s about Sept. 27.

Once the corn reaches black layer, it then relies on the simple physics to dry down to a harvestable moisture. Corn this season will reach black layer and try to dry down in September and early October, when the day length is shorter and temperatures historically are cooler. Those shorter days and cooler temperatures will slow dry down of the corn kernels. Barring a sudden and dramatic shift in the current weather, corn harvest in Kentucky will be late. If September ends up being one of the hottest and driest on record, then disregard the previous comments. However, if September is “normal” or follows the current weather patterns, producers need to look at what should be a good harvest, but a late and wet harvest, and prepare their bins and driers now.