Louisiana Corn Crop Update

By Matt Foster, Ph.D.

LSU AgCenter

While some early corn is starting to be harvested in the state, some of the crop is still at the R5 growth stage (dent). After looking at several fields and speaking with consultants and extension agents, corn maturation has been slower than usual this year due to moderate temperatures, high humidity, and high rainfall amounts. As the corn crop approaches maturity, one of the most important management decisions a producer will make is when to terminate irrigation. Factors such as estimated time to maturity and soil moisture should be considered when making this decision. Assuming the crop is “already made” at R5 can cause problems if soil moisture becomes limiting prior to physiological maturity or blacklayer (R6). Previous research has shown that terminating irrigation too soon during the R5 growth stage can reduce grain yield by up to 20% since corn kernels continue to gain weight and size until R6. Recent rains will be sufficient for some fields, but some may require irrigation with the hot and dry conditions predicted for the next couple of weeks. 

Staging corn at the R5 growth stage is done by monitoring the milk line. To see the milk line, break a corn ear in half and look at the cross-section of the top half of the ear. The starchy solid interior portion moves from the top of the kernel toward the cob as the kernel matures. Kernels within the R5 growth stage are specifically designated by the progression of the milk line: one-quarter, one-half or three-quarters. Progression of the milk line and time required between each quarter are temperature, moisture, and hybrid dependent. It generally takes around 24 days for the milk line to progress through the entire kernel profile. 

Following the progression of the milk line during R5 is a good way to estimate when a field will reach R6. This stage can be identified by a black layer at the tip of the kernel. Once a field reaches blacklayer, irrigation can be terminated since any stress has little effect on grain yield. Remember, “Dent doesn’t mean done.”