It is time to begin evaluating your corn fields now.
After the corn silks have turned brown, we can easily look at the ear girth—number of rows of kernels. This maximum girth aspect for the corn is determined at V5 to V6 growth stage—8 to 12 inch tall corn.
From the maximum girth potential, the actual girth will be influenced by the weather, the nutrient status, and the plant energy supply.
Individual ears will always have even numbers of rows, but a population of ears can have any number of rows. As you increase the average ear girth from 15 rows to 16 rows, yield will increase by 7 to 10 Bu/A. In my 111 day corn, I am finding 18 and 20 rowed corn.