As of July 19, the USDA National Agricultural Statistics Service reports that 59 percent of the nation’s corn crop is silking. Pollination and silking are two of the most important stages in corn progress and vital in determining grain fill and, ultimately, yield. Here are a few things to keep in mind as you begin to see silks and pollen shed in your fields.
- Development and Timing. Silk emergence (R1 growth stage) is the start of the reproductive period in corn. Traditionally, silking and pollen shed have been thought of as having to occur simultaneously for successful reproduction. However, through Stine’s breeding program, we discovered that some of the most stress-tolerant plants silk earlier than pollen shed. This allows a greater window for pollination, especially during drought stress when silking can be delayed. Silks begin forming at the base of the ear and move up to the tip of the ear. They will not stop growing (or elongating) until pollinated. Each kernel on the ear has a silk. A single ear is estimated to have anywhere between 750 to 1,000 kernels. Not every kernel is successfully pollinated, so most ears (in a good year) will produce only 400 to 600 kernels.
As silks emerge, anthers (which are located on the tassels) should be visible. Anthers are pollen-containing sacs that open up during pollination. After they have released their pollen, they may remain hanging from the tassel for several days or weeks. After temperatures rise from their overnight lows and relative humidity drops, this triggers the anthers to release their pollen, so pollen shed typically happens between 8 and 11 a.m. Each tassel contains roughly 6,000 anthers, and these anthers (from one tassel) release anywhere between 2 to 5 million plus pollen grains. In most cases, these pollen grains do not pollinate the same plant they originate from. Grains can travel with the wind and typically disperse throughout the same field.
As for timing, silks are typically fully emerged when pollination occurs. Once pollen shed occurs, the fertilization process should take around 24 hours. A whole field can take up to 14 days before it is successfully and entirely pollinated. Once successfully pollinated, the silks will detach from the kernel and begin to dry up (or turn brown). - Threats/vulnerabilities.
Corn plants are very vulnerable to environmental stressors during silking and pollination. Certain conditions can lead to kernel abortion or abnormalities in kernel weight. Specific threats include:
Extreme heat/drought stress — Consistent high temperatures can lower the rate of pollination as heat can kill pollen before it reaches the silk. A few days of above-average temperatures may not cause much damage, but repeated high temperatures can mean trouble ahead.
Wet conditions — Anthers will not open under wet conditions, and pollen will not shed from closed anthers. Essentially, frequent and persistent rains may greatly impact pollen shed.
Poor timing of pollen shed with silk emergence — Sometimes the two stages aren’t synched, which results from heat or drought stress. If high temperatures are persistent before silking, there’s a chance silks won’t emerge or will be delayed and not synch with pollen shed, which could lead to kernel abortion. You might see the effects of this more toward the tips of the ear because the ear pollinates first from the base and then moves outward to the tip. - Evaluating pollination success.
There are two ways to determine if your corn crop was successfully pollinated.
Ear shake test — To do this, slightly open the husks at the top of the ear and shake the ear. If dark, curled up silks fall out, it’s a good indication that corn pollination has taken place. When corn has been pollinated, the silks dry up, turn brownish in color and can fall off. You’ll want to repeat this test in a few different areas throughout your field. Remember, it could take up to 14 days before an entire field is successfully pollinated.
Blister test — After pollination has successfully taken place, around the R2 stage (10–12 days after silking), you can pull back the husks and examine the ear. At this stage, the ear ovules appear like white “blisters” before taking on the appearance of kernels.
For questions about corn silking and pollination or if you detect pollination abnormalities in your field this growing season, contact your local Stine agronomist to discuss next steps.