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5 effects of stress during corn's grain-fill period

5 effects of stress during corn's grain-fill period
Breeder's Journal: Stress could play a role in grain fill in corn.

Rains during spring and early summer set records in some areas of the Corn Belt, causing emergence problems and weak root development. I saw "rootless syndrome," where plants developed primary roots but only one or two secondary roots. Some fields showed nitrogen loss that even affected pollination, causing poor ear-tip fills.

Leaf diseases like northern corn leaf blight and gray leaf spot were rampant in some areas, although not everywhere. Where severe, they caused additional stress on the corn crop. Five possible effects of this stressful environment on grain fill are indicated below.

DOUBLE WHAMMY: When corn plants are stressed by drought and heat, expect to find poorly pollinated ears during grain fill.

1. Poor kernel set. Pollination is the most critical period for getting good kernel set. For grain fill, 50 to 60 days is needed after pollination, depending on the relative maturity of the hybrid and the temperatures prevailing in the area. The primary focus of plants at this time is to fully develop kernels. Corn likes cooler temperatures and sufficient water during this critical period. Any stresses during grain fill will have a negative effect on yield. Corn plants try to fully develop and mature as many kernels as possible, which were set during the pollination period.

2. Incomplete kernel set. If the pollination of some ovules is not successful due to stress, it could result in incomplete kernel set. Japanese beetles or corn rootworm beetles, which feed on pollen that falls on silks, can interfere with pollination and reduce kernel set. Severe heat, moisture or disease stress during grain fill may cause plants to start cannibalizing their leaves and stalks to fulfill the growing needs of their progeny. Heat and drought stress might have delayed silk emergence and caused pollination problems. Late-emerging silks may not have found any pollen left in the field for fertilization.

3. Tip-fill issues. The first silks to emerge come from the butt, and the last silks emerge from the tip. So kernels near the tip are more prone to be left out of the pollination process. That’s why some growers plant pairs of hybrids that are two to three days apart in their pollen-shed dates in alternate strips in each field. When pairing hybrids, try to use two hybrids from the same seed company to make sure they differ in days to pollen shed. Sometimes hybrids from different companies with different relative maturity days may be similar in days to pollen shed.   

4. Aborted kernels. Plants don’t like to produce runts. So if there is stress during grain fill, plants start to abort the youngest kernels, causing tip dieback, so the remaining seeds can fully develop. The physiologic maturity or black layer occurs at 32% to 35% grain moisture. Stress before this period can cause kernel abortion and light test weight.

5. Stalk rot. If plants divert nutrients from stalks to “feed” seeds, it can lead to premature death and susceptibility to stalk rot pathogens. Try to keep your crops as “comfortable” and well-fed as possible. This helps avoid any stresses in their life, and they will reward you with good yields.

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

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