Following a prolonged period of mid-season drought conditions, corn stalks have been drying down very quickly over the past few weeks in many areas. Monitoring kernel development during this time is critical for late-season irrigation decisions, and helps manage harvest plans and expectations.
With very few exceptions, Tennessee experienced favorable conditions during the majority of the corn pollination window this year. Heat and drought stress during this time were minimal with night temperatures staying out of the 80’s. Relatively mild temperatures and substantive rainfall during May sustained us through tassel emergence and pollination.
However, many areas of West Tennessee are now approaching 40 – 50 days without substantive rainfall. Experience tells me we are about 2-weeks ahead of where we’d really like to be at this point relative to the physiological maturity of the corn crop in most areas.
Tip Back
Tip Back is a catch-all term for failed pollination sites or aborted kernels. The vast majority of tip back that I have observed this year has been due to kernel abortion (Figure 1), since we made it through the pollination window pretty much unscathed. Pollination and ear development begins at the rear of the ear and progresses toward the tip. With the limited rainfall received during the previous 6-weeks, plants have simply not had the resources to fill out all of the positions that were pollinated. When yield limiting conditions are present, this is a desirable plant response, since it is better for a plant to concentrate its energy on developing the positions (kernels) toward the base of the ear rather than stretch itself too thin and expend too much energy on moving nutrients to the very tip of the ear.
Keeping a consistent eye on corn progression during this time allows us to monitor crop water use and demand (especially on irrigated acres) and how fast the corn is progressing toward black layer (R6), and full physiological maturity.
As we progress through R5 (Figure 2), reach R6, and continue to harvest maturity, grain moisture loss occurs at about 0.5% per day, or 1% every 2 days. Heat, wind, humidity, and individual hybrid genetics can impact the rate at which corn dries down.
Milk Line Progression
Beginning at or a few days after R5, sampling ears and looking at the milk line is a great way to monitor how fast kernels in the ear are maturing during this time.
Again, remember that the ear develops from the back to the front, or rear to the tip. If you sample often enough, you will see kernels at the back of the ear hit “dent” first, and then progress to the front. Additionally, maturity progression happens from the top down. This is the reason we are able to see and track the progression of the milk line. As starch begins to accumulate and harden, it does so at the “top” of the kernel first and then progresses down toward the cob (Figure 3).
Take an ear in both hands, with the tip in your left hand and the end in your right and break it in half. The milk line will be visible on the kernels in your left hand because that is the rear face of those kernels. There will be no visible milk line on the kernels in your right hand because that is the forward face of those kernels (Figure 4).
