As the season starts to wind down it is important to know when your corn fields are going to be reaching physiological maturity, also known as black layer. Black layer usually occurs 55-65 days after silking, and it is when dry kernel weight reaches its maximum and dry weight accumulation stops. A black layer or film is seen at the end of the kernel and seals the kernel off from further development or increase in test weight. You can physically check your fields for black layer, or you can calculate your growing degree units to see if your needs have been met.
What Are Growing Degree Units
Growing degree units (GDU’S) are used to estimate the growth and development of certain crops and pests throughout the growing season. It is a measurement of heat or temperature units above a base temperature. Corn plants require a certain number of GDU’s to reach maturity no matter how many calendar days it takes to get there.
An early maturing corn variety may progress through growth stages faster than a later maturing variety. For example, a 95-day hybrid needs around 2,400 GDU’s from planting to maturity while a mid-season 110-day hybrid will need around 2,750 growing degree days from planting to maturity.
Location and climate plays a major factor in GDU accumulation. Knowing how many GDU’s have accumulated in your field and how many GDU’s are needed to reach maturity for your specific varieties can help you determine when black layer will occur and when you may be able to start harvest.
How to Calculate GDU’S
You can calculate GDU’s by using a simple equation: (Daily Maximum Air Temperature + Daily Minimum Temperature)/2-50. For calculating corn GDU’s there is a minimum temperature of 50 and a maximum temperature of 86. So, whenever we have temperatures below 50 degrees the equation will default to 50 and if temperatures are over 86 degrees the equation will default to 86 degrees. The resulting number from the equation above will be the amount of GDU’s that have accumulated for that day.
Luckily, you don’t have to do that math: The EarthScout App will do it for you!
EarthScout sensors collect hyper-local weather data points in your field including temperature and use that data to calculate field specific GDU’s. Using nearby weather stations to calculate GDU’s, is not nearly as accurate as data coming right out of your field.
All you need to do is enter your planting date and end date into the web or mobile app and a graph will appear with the amount of GDU’s that have accumulated in that specific field.
Actual EarthScout Data
We have one EarthScout unit in southern Minnesota (red star) and another EarthScout unit in Southern Indiana (blue star) they are about 9 hours apart from each other.
The difference between locations has an obvious effect on accumulated GDU’s so far this growing season. From May 16th-August 31st the Minnesota EarthScout (red star) unit has recorded 1,296 GDU’s while the EarthScout unit in southern Indiana (blue star) has recorded 1,416 GDU’s.
EarthScout units collect valuable hyper-local data from your fields allowing you to make data driven decisions on your farm. The more you know about your fields’ specific GDU’s the better you can understand how your crops move throughout life stages, how to select varieties based off GDU’s in your area and how to predict end of season harvest times. Calculating and knowing your specific field GDU’s throughout the season can also predict important things like pest and disease emergence.
If you would like to learn more about how EarthScout can help you calculate GDU and make better cropping decisions, visit EarthScout.com, or contact an EarthScout Grow Coach today at 877-443-7632.
Anna Kelley is a Technical Agronomist for EarthScout. Anna is a graduate of Northwest Missouri State University with a degree in Agronomy and GIS with an emphasis in precision ag. Her specialties at EarthScout include grain crops, irrigation management and precision ag.
Coulter, J. (2021) Selecting corn hybrids for grain production. University of Minnesota Extension. https://extension.umn.edu/corn-hybrid-selection/selecting-corn-hybrids-grain-production#sources-417010
Carter, R. Kernel Black Layer Formation in Corn Anatomy, Physiology, and Causes. Pioneer. https://www.pioneer.com/us/agronomy/kernel-black-layer-formation.html
Nielsen, R.L. (2021) Grain Fill Stages in Corn. Agronomy Department, Perdue University. https://www.agry.purdue.edu/ext/corn/news/timeless/GrainFill.html
Elmore, R., Daugherty, R.B, Mueller, N. (2015) Growing degree Units and Corn Emergence. https://cropwatch.unl.edu/growing-degree-units-and-corn-emergence
Neild, R.E., Newman, J. E. Growing season Characteristics and requirements in the Corn Belt. Perdue University. https://www.extension.purdue.edu/extmedia/nch/nch-40.html