Management Decisions Depend Upon Corn Pollination Success
July 14, 2005 12(19):148-149
Joe Lauer, Corn Agronomist
Cornfield condition is quite variable in Wisconsin at this time. Some fields have
received adequate to excessive rainfall, while others are in the midst of one of
the worst droughts recorded. USDA-NASS on July 11 rated Wisconsin's corn crop as
3% very poor, 7% poor, 21% fair, 45% good and 24% excellent. Severely stressed corn
is commonly observed in an approximately 50-75 mile wide band extending from west
of Madison towards the NE to Manitowoc. Remnants of hurricane "Dennis"
have provided some relief in SE Wisconsin. Lighter soils and knolls have more leaf
rolling and stress. The southern half of the state has started to tassel and many
farmers feel that the dry weather is beginning to reduce yield potential.
Critical period during the corn life cycle
With the onset of tasseling the corn crop is in a critical growth and development
stage for grain yield. The tasseling, silking, and pollination stages of corn development
are extremely critical because the yield components of ear and kernel number can
no longer be increased by the plant and the potential size of the kernel is being
For example, the potential number of ears per unit area is largely determined by
number of seeds planted, how many germinate, and eventually emerge. Attrition of
plants through disease, unfurling underground, insects, mammal and bird damage,
chemical damage, mechanical damage, and lodging all will decrease the actual number
of ears that are eventually harvested. The plant often can compensate for early
losses by producing a second or third ear, but the capacity to compensate ear number
is largely lost by R1 and from then on no new ears can be formed.
Likewise, kernel number is at its greatest potential slightly before R1, the actual
number of kernels formed is determined by pollination of the kernel ovule. The yield
component of kernel number is actually set by pollination and fertilization of the
kernel ovule. If the ovule is not pollinated, the kernel cannot continue development
and eventually dies. No new kernels form after the pollination phase is past.
The only yield component remaining with some flexibility is kernel weight. For the
first 7 to 10 days after pollination of an individual kernel, cell division occurs
in the endosperm. The potential number of cells that can accumulate starch is determined.
At black layer formation (R6) no more material can be transported into the kernel
and yield is determined.
Determining the success of pollination
Over the next couple of weeks, the key plant indicator to observe and base future
management decisions upon is the success of pollination. Each ovule (potential kernel)
has a silk attached to it. When a pollen grain falls on a silk, it germinates, produces
a pollen tube that grows the length of the silk which fertilizes the ovule in 12
to 28 hours. If fertilization of the ovule is successful, within 1 to 3 days the
silk will detach from the developing kernel. Silks will remain attached to unfertilized
ovules and be receptive to pollen up to 7 days after emergence. Silks eventually
turn brown and dry up after pollination is over.
Two techniques are commonly used to assess pollination success or failure.
The most rapid technique to determine pollination success is the "shake test."
Carefully unwrap the ear husk leaves and then gently shake the ear. The silks from
fertilized ovules will drop off. The proportion (%) of silks dropping off the ear
indicates the proportion of future kernels on an ear. Randomly sample several ears
in a field to estimate the success of pollination.
The second technique is to wait until 10 days after fertilization of the ovules.
The developing ovules (kernels) will appear as watery blisters (the "blister"
R2 stage of kernel development).
Typical management options and uses are available for corn that has successfully
pollinated. If pollination is unsuccessful, we are usually trying to make the best
of a bad situation. This year it looks like drought will be the major factor affecting
Drought-stressed corn can be grazed or used for forage, either as green chop or
silage. Because of the potential for nitrate toxicity, grazing or green chopping
should be done only when emergency feed is needed. The decision to chop corn for
silage should be made when:
- You are sure pollination and fertilization of kernels
will not or did not occur and that whole-plant moisture is in the proper
range for the storage structure so that fermentation can occur without seepage or
spoilage losses. If there is no grain now, florets on the ear were either not pollinated
or have not started to grow due to moisture stress, and the plant will continue
to be barren. If the plant is dead, harvest should occur when whole plant moisture
is appropriate for preservation and storage.
- If pollination and fertilization of kernels
did occur but it was poor, do not chop until you are sure that there is no
further potential to increase grain dry matter and whole plant moisture is in the
proper range for the storage structure. These kernels may grow some now, if the
plant is not dead and in those fields receiving rain. If kernels are growing dry
matter is accumulating and yield and quality of the forage is improving.
Green, barren stalks will contain 75-90% water. If weather remains hot and dry,
moisture content drops, but if rain occurs before plants lose green color, plants
can remain green until frost. Drought stressed corn has increased sugar content,
higher crude protein, higher crude fiber and more digestible fiber than normal corn
silage. Drought generally reduces yield and grain content resulting in increased
fiber content, but this is often accompanied by lower lignin production that increases