Here is some corn that is now denting (R5). We are getting closer to physiological maturity. At this time, the crop is still needing water but less than before. Once the milk line progresses to the bottom of the kernel, we will see the ‘black layer’ form. We can then cut off irrigation. In the photo below, you will also notice the “milk line.” This is the separation between the softer doughy white portion close to the cob and the starchy, solid portion at the top.
When we stage kernels in R5, we look at the milk line: 1/4, 1/2, or 3/4. This is good for observing kernel development. Progression of the milk line varies due to temperature, moisture, and hybrid maturity. Here is a table from “Corn Growth & Development” that shows the expected trend:
Southern rust can still hurt us until about 1/2 milk line. We have sprayed most everything for rust right now, but there are reports of rust in many fields still. This is a good time to evaluate the control we got from gungicides. We may also look for stinkbug damage on field borders. If the ears are curved, the damage from SB was early. If individual kernels are damaged, damage from SB occurred late.