Corn Reproductive Development Facts

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Image: Silks on a corn plant

• The tip of the emerging corn tassel may be noted as early as the V13 growth stage to as late as the V17 growth stage.
• The tassel is usually fully emerged and open before any pollen is shed.
• The first silks will emerge about 3 days after pollen shed begins.
• Below is a summary of the processes that take place during the reproductive stages of corn.

Silks emerge from kernels at the tip of the ear last and are least likely to be fertilized if the plant is under stress. Kernels at the tip may abort following fertilization if the plant becomes stressed during grain fill.

Silks are the female part of the flowers. Every potential kernel (ovule) on an ear develops its own silk that must be pollinated for the ovary to be fertilized and develop into a kernel. Typically, up to 1000 ovules form per ear, even though we typically harvest only 400 to 600 actual kernels per ear  (Bob Nielsen, Purdue University).

Pollen grain germination occurs within minutes after a pollen grain lands on a receptive silk. A pollen tube, containing the male genetic material, develops and grows inside the silk and fertilizes the ovary within 24 hours. Pollen grains can land and germinate anywhere along the length of an exposed silk. Under hot, dry conditions, the silks dry rapidly and may not contain enough moisture to support pollen grain germination or pollen tube growth (Bob Nielsen, Purdue University).

Pollen shed is not a continuous process. The release of pollen will stop when the tassel is either too wet or too dry and starts again when moisture and temperature conditions are favorable. Peak pollen shed usually occurs between 9:00 and 11:00 a.m.

Pollen is not likely to be washed off of silks during a rain. Pollen that is shed prior to a rain usually attaches itself to the silks so quickly that it is not likely to be washed off.

Scout fields for silk clipping. Silk clipping by insects not only removes viable silk tissue, but also injures a certain length of the remaining silk. Generally, silks should extend at least 1/2 inch beyond the husk to ensure that a sufficient length of uninjured silk tissue is exposed to capture viable pollen. 

Silks will take 2 to 7 days to emerge. With adequate moisture, the silks will grow 1 to 1 ½ inches each day and continue to grow until fertilized. The ability of the silk to receive pollen generally exists up to 10 days after silk emergence. After 10 days, the ability of the silk to receive pollen decreases rapidly. Silk elongation continues until pollination is successful, although elongation eventually ceases as unfertilized silks senesce. 

The tassel is usually fully emerged and open before any pollen is shed. The length of pollen shed varies but is usually 5 to 8 days with the peak production coming about the third day. The first silks will emerge about 3 days after pollen shed begins.

Silking is delayed more than tasseling when the corn plant is under moisture stress. Under extreme drought conditions, the silks grow slowly and may not emerge from the husks before the pollen is shed.   Emergence of silks after pollen has been shed is commonly referred to as “missing the nick” and results in poor to complete lack of kernel set.  

Moisture stress during any period of corn development can impact yield potential.  Stress during early vegetative development has less effect on yield than similar stress during the pollination period. The table below lists the estimated loss in yield potential at various stages when corn plants show severe wilting for 4 consecutive days.

Estimated loss in yield potential at various stages of growth when corn plants show severe wilting for 4 consecutive days.

Check pollination in the field. Each potential kernel has a corresponding silk. About 2 days after pollination, the silk will detach from the developing kernel. Carefully remove the husks and gently shake the developing ear.  Silks that remain attached indicate those embryos have not been pollinated.

Corn leaves may roll even when adequate moisture is present. Temperatures of 90º F or greater cause loss of water vapor from the leave surface (transpiration) to exceed water uptake by the roots. Leaves roll to minimize the surface area exposed to the drier air as well as to create a more humid environment inside the rolled leaf. Once the plant’s ability to provide moisture meets or exceeds the plant’s transpiration demand, the leaves will unroll, usually toward the evening hours on hot, windy days. Leaves that remain rolled overnight suggest that the moisture stress will likely impact plant growth and yield.

Yellowing of the lower corn leaves just prior to or soon after pollination suggests the plant roots to not have access to enough available nitrogen to meet plant demands, whether from an inadequate supply of available nitrogen or from a restricted root system caused by dry weather, compaction, herbicide injury, and/or heavy rootworm feeding. Movement of nitrogen from the lower plant parts (stalk and leaves) soon after pollination dramatically increases the likelihood of stalk rots prior to normal physiological maturity.

Nitrogen deficiency is easily identified as a yellowing inverted “V” down the midrib of the lower leaves. Nitrogen is mobile within the plant allowing it to be moved from the older, established lower leaf and stalk area to the filling grain.