• The number of kernels set is largely determined near the time of pollination.
• Yield losses due to reduced kernel set at pollination cannot be fully regained.

Kernel set requires the successful completion of several plant processes.

• Production of viable pollen by the tassel
• Interception of pollen by receptive silks
• Fertilization
• Embryo and endosperm development

• 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

• 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 at Pollination Can Reduce Yield

• 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

• 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.

• 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.

• 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.

• 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.