Let's talk about cob size. At this time of year the the most common method of estimating corn yield potential is to eyeball the size of the cobs. I have heard comments from growers impressed with how big their cobs are and also just as many comments from growers who are concerned their cobs are not big enough. (Insert your own wisecrack here)
Does size matter? Not as much as you might think. I will use 38M58/38M59 as an example because it has a small ear. This hybrid has been a dominant force in the 28-2900 heat unit maturity range since it was introduced in 2006. Every August customers call expressing concern that their 38M58 genetics has very small cobs. "How can it yield with these small cobs?" Every year I agree with them that it has small cobs, but we all have to wait and see what the scales at the elevator tell us. The story always ends with customers ordering more 38M58 genetics for next year.
This is 38M58 on the left and DeKalb 43-27 on the right. The Dekalb hybrid has more 2 more rows of kernels giving it a more girthy look. But, 38M58 has a smaller core and bigger kernels. The kernel to cob ratio is known as shelling percentage and 38M58 has a higher shelling percentage than most other hybrids. 38M58 is also a heavy test weight hybrid and we cannot measure test weight with our eyes.
One last thing to note is depth of kernel. High yielding hybrids have the ability to increase their kernel depth which contributes directly to yield and test weight. This is called kernel flex and I believe this trait is more important than ear flex when determining yield.
Will 38M58/38M59 do well this year? Time and weigh scales will tell us. The hybrid has the same small ears as usual. The long summer may give fuller season hybrids an advantage against 38M58, I still predict it to be a very competitive hybrid in its maturity.