Pollination in the Corn Field
Dave Den Boer, CCA-ON Product Development Agronomy Manager
A good portion of the Ontario corn crop has either started or over the next few weeks will
undergo pollination. This is one of the most critical stages in the life of a corn plant.
Unfortunately, pollination is also one of the least controllable aspects of grain production since
its success or failure is mainly influenced by environmental conditions. At this stage, the corn
plant is switching from the vegetative stage of the corn plant to the reproductive stage. We’ll
see this switch when tassels & silks start appearing. From this point forward all of the corn
plant’s resources are going to be used to produce grain.
The Tassel
The corn tassel is the male flower of corn. The tassel has been developing deep in the whorl
of the plant since approximately the 6th leaf stage. The tassel consists of many spikelets,
which are located along the main spike and lateral branches of the tassel. Anthers emerge
from these spikelets. An individual tassel produces approximately 6,000 pollen-bearing
anthers, although different hybrids can vary greatly for this number. The pollen grains are held
on the anthers, which are located at the end of a thin stem called the filament.
The Process: Pollination and Fertilization
Pollen landing on silks is called "Pollination."
The successful merging of the pollen with the ovule is called "Fertilization."
Pollen (yellow dust-like) grains are contained in anthers. An anther can have from 2 to 25
million pollen grains. The anthers open and the pollen grains pour out, but only after the
tassel is dry. Pollen is light and can be carried up to 600 feet by wind. However, most of it
drops within the first 20 to 50 feet. Pollen shed is not a continuous process. It stops when the
tassel is too wet or too dry and begins again when temperature conditions are favourable. A
pollen grain stands little chance of being washed off the silk during rain storms as little to none
is shed when the tassel is wet.
Each pollen grain contains the male genetic material necessary for fertilizing the ovary of one
potential kernel. Under favourable conditions, pollen that lands on a silk is captured by fine,
sticky hairs on the surface of the silk. The pollen grain germinates immediately, producing a
pollen tube that grows down the length of the silk, resulting in fertilization of the ovule within
12 to 28 hours. Although many pollen grains may germinate along the surface of the silk, only
one grain will generate a pollen tube resulting in fertilization. Pollen from a corn plant rarely
fertilizes the silks of the same plant. Silk elongation begins 7 to 10 days prior to silk
emergence from the husk. 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. The silks
from near the base of the ear emerge first and those from the tip appear last. Under good
conditions, all silks will emerge and be ready for pollination within 3 to 5 days and this usually
provides adequate time for all silks to be pollinated before pollen shed stops.
The Ear
Beginning at about the 6th leaf stage, potential ears are initiated at each node up to the 12th to
14th leaf node, but it is normally only the uppermost ear that fully develops. The female ovules
that will become kernels upon successful fertilization, are located in paired rows along the
surface of the ear. A primary ear may develop up to 1000 ovules,
of which only around 400-700 will be fertilized and harvested as
corn kernels. .
A little cooler temperatures for the next two weeks is a good thing!
Long range temperatures for the next 10 -14 days show 20-27 celcius will be common. Mid 20
degree celcius daytime temperatures and low 20 degree celcius night temperatures are ideal
for pollinations. This combination of day and night temperatures maximizes photosynthesis
during the day and minimizes respiration during the night. These temperatures will maximize
pollination, fertilization and kernel growth rate. Extreme heat stress (37 celcius or greater) can
kill corn pollen. Fortunately corn pollen does not mature or shed all at once. Pollen maturity
and shed occur over several days and up to two weeks. Therefore, a day or two of very high
heat usually does not affect the entire pollen supply.
Rain Helps Fill the Corn Cob
Looking at the extended forecast, there are 3 or 4 good chances over the next couple weeks
for rainfall. If we get some timely moisture along with the excellent daytime and night time
temperatures forecasted, we could be looking at a big corn crop from the pollination
perspective.