A website from UGA Cooperative Extension
Starch/Milk Line Progression

I have scouted several corn fields recently, and I noticed many of them are starting to reach physical maturity. This brings about the question, “When is it the time to stop irrigating corn?”

A good way to way to determine how much longer you need to water is to look at an ear of corn and find the milk line. This milk line develops shortly after the corn reaches the dent stage. The dent stage occurs when the corn begins to develop a dent on the crown of the kernel. The corn will usually reach the dent stage at around 31-33 days after silking. About seven days after the dent stage begins, the milk line will start to separate the milky liquid from the solid starch. The starch will start at the top of the kernel and then make its way down to the cobb in the center.

To take a sample, pull 6-8 ears from multiple spots in the field to get an average representation of the field. Then, break the ears in half and look at the progression of the milk line from the outside of the kernel towards the inner cobb. It is important to maintain good soil moisture until the starch/milk line is progressing from 50 to 75 percent before the irrigation is turned off.  Stress on the corn during this time can still cause 15-20 percent yield loss if the irrigation is turned off too early. Good soil moisture is also important so the corn plants aren’t using energy from the stalks to finish grain fill because this could weaken the stalk and lead to lodging.

If you would like to learn more about determining the proper time to stop irrigating your corn, check out these other educational posts from Extension personnel. You can also contact your local County Extension Agent.

Black Layer in Corn

Grain Fill Stages in Corn

Black Layer on Right Hand Kernel