How does it feel knowing your huge investment in a corn crop rides on what happens during a handful of days centered around silking and pollination? It’s a miraculous process, but it also can be temperamental, heavily dependent upon weather and other variables outside of your control.
Here is a closer look at how silking and pollination unfold when everything works properly. Providing insight are Mark Licht, Iowa State Extension cropping systems specialist; Dan Quinn, Purdue Extension corn specialist; Mark Jeschke, Pioneer agronomy manager; and Stephen Strachan, Pioneer research agronomist. Strachan and his team performed research where they only allowed silks to be pollinated on certain days, helping gain insight into the larger overall pollination process.
Here are 12 facts that help explain the intricacies of pollination:
1. Silking period is most sensitive to stress. Iowa State University’s “Corn Growth and Development” publication leads off the description of the silking phase, R1, by noting that the crop is most sensitive to stress at this point. Any stress can reduce kernel number per ear, Licht says.
2. Silks and pollen shed must match. Silks on the primary ear must be present and receptive when pollen shed, also called anthesis, occurs. Quinn notes that drought is often thought of as the main culprit that can prevent pollen shed and silking from nicking, or lining up. However, other unusual weather patterns can also throw a monkey wrench into timing.
3. Pollen grains fall quickly. In the absence of wind, pollen grains fall from anthers at about 8 inches per second. That means in calm settings, it takes less than a minute for pollen grains to land on receptive silks, Jeschke observes.
4. Pollen tubes are conduits. Research reviews by Jeschke indicate that a pollen grain begins extruding a pollen tube and penetrating a silk within about 15 minutes after the silk captures the fallen pollen grain. It’s a delicate process that happens quickly, millions of times over within a cornfield.
5. Moisture stress extends process. If plants are under stress, silks are longer and it takes the pollen tube more time, even more than 24 hours, to complete its growth. However, Strachan notes in “Pollination of Corn: Timeline of Key Steps” that under favorable conditions, pollen tubes complete their growth in 12 to 18 hours. Once complete, there is a channel for genetic material to move from the pollen grain to the receptive female embryo, resulting in fertilization and formation of a single kernel.
6. Fertilization window is five days. Silks attached to the base or butt of the ear emerge first from husk leaves, Licht notes. Once emerged, the clock begins ticking. A silk can be fertilized by a single pollen grain, landing anywhere on the exposed silk, for around five days.
7. Silks at tip may miss out. Silks attached to potential kernels near the ear tip emerge last. If pollen shed is already over by the time they emerge, they may not be fertilized, Licht says. When potential kernels simply don’t develop into harvestable kernels, they may still be visible on the ear as small, undeveloped white mounds of matter.
8. Fertilization happens within two days. If you could observe fertilization at the moment it occurs inside the pollen tube, here is what you would see, according to Strachan. One male nucleus fertilizes the egg nucleus to create what becomes the seed embryo in a corn kernel. Then, a second male nucleus fertilizes two polar nuclei to form what becomes starch in a corn kernel. The embryo and start of starch formation happens by about 40 hours after pollination.
9. Fertilized silks detach. Once an embryo forms, cells begin drying out. With food no longer available, the silk detaches from the embryo. The point where the silk detaches creates a silk scar that you can still see on some kernels, depending upon the hybrid, Strachan notes. These silk scars typically show up about five days after pollination.
10. Ears keep growing. If you think ears seem longer after you return to do harvest checks than when you checked for pollination success, you are not imagining things. In fact, Licht says that rapid elongation of the ear begins during R1. Ears may only be 40% to 45% of their final length as fertilization wraps up.
11. Shake test determines success. The time-honored method for determining how many kernels were fertilized is to pull back shucks, hold an ear horizontally and shake it, Quinn says. If kernels were formed, those silks will fall off. Remaining silks represent potential kernels that were not fertilized.
12. Alternate method: Observe silks. Pulling back shucks takes time and is destructive. Strachan explains that you can estimate whether pollination occurred by observing for wilted silks and reduced silk elasticity instead. Silks with these properties are fertilized, and you don’t destroy the ear to make the determination.