Pollinating under adverse conditions

By John Brien, AgriGold Agronomist, CCA

About a third of Ohio’s corn crop is tasseled and more is tasseling every day, the temperatures and humidity continue to be high and the forecast continues to predict heat. How will all these factors affect pollination out in the corn field?

Ideal pollination conditions consist of moderate temperatures with low humidity with ample soil moisture; unfortunately some parts of the state only have ample soil moisture. So if conditions are not ideal how does a corn plant ensure the best pollination possible? To ensure a successful pollination the corn plant has many built in safety measures.

The first safety measure surrounds pollen release. A tassel will not begin releasing pollen until the entire tassel is emerged from the plant. Pollen will also not be released when conditions could be detrimental to the pollen grain. Typically pollen is released once the dew is off the corn plant in the morning and prior to the heat of the day and again in the evening as the temperatures decrease, ensuring pollen viability.

The second safety net surrounds the silk. The corn plant will begin releasing pollen a couple days prior to silk emergence, thus ensuring the newly emerging silk will have ample opportunity to be fertilized. The silks also do not emerge all at once; the silks grow from the bottom of the ear to the top thus allowing each silk time to be exposed to pollen.

The third safety net is redundancy. A single corn plant has the ability to produce two to five million grains of pollen, enough to provide 2,000 to 5,000 grains of pollen per silk. Keeping in mind only one pollen grain is needed to fertilize one kernel. The safety nets of a corn plant will greatly limit the potential for a complete pollination failure, but what could cause a reduction in pollination success in 2011?

There are really only three events that could limit the success of pollination in 2011: water stress, heat stress and excessive silk growth.

Plants under excessive moisture stress can cause delayed or even incomplete silk emergence. Silks have the greatest water content of any corn plant tissue and thus are most sensitive to inadequate moisture levels in the plant. When there is a moisture shortage, silk elongation can be delayed or even stopped, while pollen release from the tassel is not affected by moisture shortages. The difference can cause pollen to be released when there are no viable silks ready to accept the pollen, causing an incomplete “nick” of pollen shed and silk emergence. The resulting symptom is uneven kernel set on the ears with many “blanks.”

Pollen viability can decrease when exposed to stressfully high temperatures and silks can die due to high temperatures and low relative humidity. The effects of heat stress on silks is probably more important because it is unlikely that massive pollen death occurs from heat stress because of when pollen is shed (mid-morning and early evening) and the length of pollen shed in a field (7-10 days).

When temperatures are warm and there is ample to excessive soil moistures silks can grow more than their normal 1-inch per day. When silks become excessively long they can act as a shield and limit the exposure of some silk to pollen. Typically the bottom side of the ear butt may not get pollinated due to being covered up by the long silks.

Pollination is absolutely essential for a corn plant to produce grain. The corn plant does all it can to ensure pollination occurs even under adverse weather conditions. Once pollination occurs, corn growers can begin to evaluate how the corn plant begins to fill and prioritize grain fill, another amazing act of a “simple” corn plant.

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