Corn Pollination Success

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Pollination Success is Critical to Final Yield

Pollination

Pollen shed or anthesis is controlled by a combination of genetic and environmental factors
Once pollen grains have matured inside corn anthers, these anthers begin to dry or dehisce
Anthers typically shed pollen around midmorning as anthers dry in the heat and sunlight
As anthers dehisce, they split apart to allow pollen grains to fall into the open air
Pollen grains are viable for only a few minutes after they are shed until they desiccate
A tassel normally sheds pollen for about 5 days
Pollen shed in a field can last up to 2 weeks

Silk Emergence

Each silk that emerges from an ear shoot connects to a single ovule, or potential kernel.
A silk must be pollinated for the ovule to develop into a kernel.
Silk emergence proceeds from the base to the tip of the ear over the course of 4 to 8 days.
Silks will continue to elongate for up to 10 days after emergence or until they are pollinated.
Silk receptivity decreases over time following emergence due to the senescence of silk tissue.

Stress susceptible period extends from 1 week prior to silking to approximately 2 weeks after silking.
Yield losses during this period result from reduction in kernel number and are therefore irreversible

Drought Effects on Silk Growth

Reduction in kernel number may result from asynchrony of pollen shed and silking.
Silk elongation requires high water potential ― drought stress can delay silking and increase the anthesis-silking interval (ASI) ― the time between the start of pollen shed and silk emergence.
Silks that emerge after most of the pollen is shed may not be pollinated.
Moderate silk delay can cause poorly filled ear tips, whereas more severe stress can result in ears that are nearly or completely barren.

Heat Effects on Pollen Shed

The location of the tassel exposes it to high radiation and potential temperature extremes.
Extreme heat stress (over 100 F) can reduce pollen production and viability.
Severe losses in pollen production or viability are necessary to affect kernel set, which would require an extended period of extremely high temperatures.

Kernel Abortion

Drought stress can prevent pollination, as well as cause successfully pollinated kernels to abort.
Drought stress causes kernel abortion by reducing photosynthesis and carbohydrate availability following pollination.

Silk Clipping

Insects such as corn rootworm beetles and Japanese beetles can interfere with pollination by clipping silks.
Clipped silks can still elongate and receive pollen; however continuous intense insect activity can result in reduced seed set.