The tassel is usually fully emerged and open before any pollen is shed. The length of pollen shed for each plant varies, but is usually 5 to 8 days with the peak production coming about the third day. It is estimated that each tassel will produce between 2 million and 25 million pollen grains. (Unfortunately, no one has counted them to confirm this.) Pollen shed usually begins at the center of the tassel and proceeds up, down, and outward on the branches.
Silks are the female part of the flowers. Every potential kernel (ovule) on an ear develops its own silk that must be pollinated in order 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)
Silking is delayed more than tasseling when the corn plant is under moisture stress. Literature often indicates that first silks typically will emerge about 3 days after pollen shed begins but many hybrids now show silks much earlier, sometimes before pollen shed starts. 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.
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. High daily temperatures, especially with low humidity, is often responsible for this, although an extended period of cloudy weather may also cause problems. Even warm nighttime temperatures can inhibit kernel set and fill.
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.
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. Fields that pollinate relatively late are often targets of large numbers of silk-feeding insects.
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. but there may be a second daily surge of pollen shed. While individual plants may shed pollen for a few days, field-wide pollen shed often lasts for up to about two weeks.
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.
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 can dry up within a few minutes following release from anthers when hot, dry conditions occur, but pollen shed usually occurs when conditions are more favorable. Viable pollen can sometimes travel ½ mile or more under favorable conditions. However, tests show that most pollen falls within the field where it originates, within about 60 feet from where it is shed.
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:
Wilting at Tassel Emergence……………………Yield Reduction of 10% to 25%
Wilting at Silk Emergence and Pollen Shed…...Yield Reduction of 40% to 50%
Wilting at the Blister Stage………………………Yield Reduction of 30% to 40%
Wilting at the Dough Stage……………………...Yield Reduction of 20% to 30%
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 that those embryos have not been pollinated.
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| 7 Days of Silk Growth
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Anthers (Pollen Bearing Structures) on Corn Tassel
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