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Corn Illustrated: The grain fill period is critical to maximizing yield.

Dave Nanda

July 4, 2017

3 Min Read
YOU WANT EARS LIKE THESE: These four ears are filled almost to the tip. Conditions remained favorable during grain fill, and this field made nearly 250 bushels per acre.

Spring rains this year set records in some areas of the Corn Belt. That caused delayed planting, emergence problems and weak root development.

In early planted fields, we noticed that 3% to 4% of seedlings were affected by seedling diseases like pythium due to cool and wet conditions, resulting in plant death. Some fields showed nitrogen loss and even affected pollination with poor ear-tip fills.

How will grain fill be affected by these conditions, especially if foliar fungicides were not used or applied on time? Here is a brief refresher on what’s important to corn plants at key times.

Pollination critical
The pollination period is the most critical time for getting good kernel set. Then comes the grain fill period; it takes 50 to 60 days after pollination is complete to reach physiological maturity, or black layer. Exact timing depends upon relative maturity of hybrids and temperatures.

This is the payoff time for the corn plant. A plant’s primary focus is to fully develop and mature as many kernels as possible. Corn likes cooler temperatures and sufficient water during this critical period for optimum yields. Any stresses during grain fill will have a negative effect on yield.

If pollination of some of the ovules isn’t successful due to stress, it could result in incomplete kernel set. Insects like Japanese beetles or corn rootworm beetles, which feed on pollen that falls on silks, can interfere with pollination and reduce kernel set.

Severe heat, lack of moisture or disease stress during grain fill may cause plants to cannibalize their stalks and leaves to fulfill the growing needs of their progeny. Heat and drought stress can delay silk emergence and cause pollination problems. Late-emerging silks may not have any pollen left in the field for fertilization.

Spread risk
The first silks to emerge come from the butt of the ear, and the last silks emerge from the tip. So the kernels near the tip are more prone to be left out of the pollination process. That’s why you might consider planting your cornfields with hybrid pairs in alternate strips in the future. Pair up hybrids that are two to three days apart in pollen-shed dates. When pairing hybrids in various fields, try to use two from the same seed company to ensure they actually differ in days to pollen shed. Sometimes hybrids from different companies with the same relative maturity rating may be similar in days to pollen shed.  

Plants don’t like to produce runts. If there’s stress during grain fill, plants start to abort the youngest kernels, causing tip dieback.

Physiological maturity, or black layer, occurs at about 32% to 35% moisture, depending on the hybrid. Stress before this period can cause kernel abortion and light test weight. If plants divert nutrients from stalks to “feed” kernels, it can lead to premature death and susceptibility to stalk rot diseases. You need to keep plants “happy” during the grain fill period to maximize yield.

Nanda is president of Agronomic Crops Consultants LLC. Email him at [email protected], or call 317-910-9876.

About the Author(s)

Dave Nanda

Dave Nanda is director of genetics for Seed Genetics Direct, Jeffersonville, Ohio. Email [email protected] or call 317-910-9876. Please leave a message.

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