Agronomy Talk

Agronomy Update

When Will My Corn Come Up?

Published on Friday, May 6, 2016

Over the past week, much of Ohio has received excess rainfall that has slowed fieldwork and planting almost to a halt. As of May 1, 2016, the USDA reported that 27 percent of Ohio’s corn was planted, but only 1 percent had emerged. With the cool, wet weather we have had, emergence is taking longer than usual. It’s tempting to look at the calendar and start to get concerned if your corn isn’t coming up in 7 to10 days like you might have expected. If you are looking at your planted fields and wondering when you will start to see rows of corn, the following information should help you understand when you might expect to see those small green spikes.

The speed of corn emergence is regulated by many factors, one of the most important being temperature. We measure the temperature over time using Growing Degree Units (GDUs), which help us quantify the amount of heat that a young corn plant has been exposed to. To calculate GDUs, first record the daily high and low temperatures. If the high is higher than 86, record it as 86. If the low is lower than 50, record it as 50. You then take the average of the high and low temperatures and subtract 50. This is the number of GDUs gained for that day.

After planting, it typically takes 110 to 120 GDUs for corn to emerge. Looking at how GDUs are calculated, you can understand how cool weather slows GDU accumulation and delays corn emergence. The chart below shows the expected emergence dates for four areas in Ohio for corn planted on April 15, April 20, and April 25.

There are several places to get information about GDUs for your own location. If you have a FARMserver™ account, you can access GDU information from the Field Focus page by clicking on “Weather Chart”. Contact your Precision Farming Field Advisor or call 317¬-565¬-4120 if you have any questions.

The Ohio State University also provides daily GDU information on the OARDC website which you can access here. If you want to do the calculations yourself, you can find past daily temperature information on weather websites such as Weather Underground. Here you would just enter your zip code and use the “calendar” feature.

Waiting for corn to emerge can be a nerve-wracking period of the growing season. While nothing can replace the sense of relief and accomplishment when the corn comes out of the ground, knowing where you stand with GDUs can at least help you feel better about your recently-planted crop.


Special thanks to Mike Hannewald, Precision Farming Field Advisor, for writing this article. If you have any questions, feel free to contact him at 317-385-2444.


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