John McGillicuddy – one of the nation's high yield corn experts – wants you to get out in your corn fields now, before you harvest to search for clues to how to increase yields next year.

McGillicuddy, of MC Agronomics, Iowa City, Iowa, speaks regularly in North Dakota for Peterson Farms Seeds, of Harwood, N.D. He says some of the best clues to what limited yields will disappear when as soon as you combine the field.

Look now at:

Plants per acre. If count is too low, investigate why. It might be related to planting depth, seed quality or planter speed. Your rate controller might be off, too. It's a common problem. Often the monitor t tells you that the planter is putting out more seed than it actually is. You need to physically check.

Ears per acre. If you have significantly fewer ears per acre than plants per acre, find out why. Seed spacing and uneven germination are common causes. Plants that are too close to each other or that emerge late compete with each other. The weaker plant often doesn't put on a harvestable ear.

Ear position. If the plant isn't filling out the top ear, you aren't getting the biggest ear. Lower ears are usually smaller. Plants don't fill the top ear if they are too close together or if they run short of nutrients or moisture. Neither may be in short supply. There might be a problem with the roots.

Ear fill. Big ears filled all the way to the tips look great. But they're also a sign that you probably didn't maximize the yield potential. Smaller cobs that are filled to within 3/4p-inch of the end tell you that they maxed out. Ears that that have kernels on the tip that started to fill, but ended up going backward is a sign that the plant ran out of nutrients before it could finish.

"There's a lot you can learn now about what you can do to get the next 25-50 bushels per acre," McGillicuddy says. "After harvest all the things you need to look at are gone."