Ag Weather Forum

Warm Nights Can Hurt Pollination

Bryce Anderson
By  Bryce Anderson , Ag Meteorologist Emeritus
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DTN forecast low temperature values compared to normal for early July have got some well-above-normal levels in store for major corn areas. (DTN graphic)

Just in time for the Fourth of July, some hot conditions are building for much of the central U.S. Weekend heat to finish out June is forecast to take a short break, but then to return in a robust way during the first week of July. Not only are the days looking pretty hot, but the nights are as well. During the weekend and early next week through July 3, overnight low temperatures in most of the U.S. Corn Belt are pegged at from seven to 12 degrees Fahrenheit above normal. That departure is actually greater than the forecast high temperatures, which over the same region are "only" predicted to be from three to 10 degrees above normal.

This tendency for warmer overnight low temperatures has been studied a great deal over almost 20 years. And, in terms of its possible impact on corn yields, it's certainly worth attention. Here is an excerpt from a University of Nebraska-Lincoln CropWatch article on how very warm overnight low temperatures can affect pollination:

"In years when we get high day and nighttime temperatures coinciding with the peak pollination period, we can expect problems. Continual heat exposure before and during pollination worsens the response ... high humidity, which helps reduce crop water demand, also increases the thermal mass of the air -- and provides extra stored heat and insulation at night.

"Corn is a "C4 Photosynthesis" plant, making it extremely efficient at capturing light and fixing CO2 into sugars. One drawback of this system is that with high daytime temperatures, the efficiency of photosynthesis decreases, so the plant makes less sugar to use or store. High nighttime temperatures increase the respiration rate of the plant, causing it to use up or waste sugars for growth and development. This results in the plant making less sugar but using up more than it would during cooler temperatures.

"Heat, especially combined with lack of water, has devastating effects on silking. If plants are slow to silk, the bulk of the pollen may already be shed and gone. Modern hybrids have vastly improved "ASI" or anthesis-silk interval (the time between mid-pollen shed and mid silk). Regardless, in some dryland fields we see seed set problems because of "nick" problems between pollen and silking.

"Even in some stressed areas within irrigated fields (extreme sandy spots, hard pans or compaction areas where water isn't absorbed and held, and some "wet spots") we can see stress-induced slow silking and resulting seed set issues. Historically, this has been the most important problem leading to yield reduction, particularly in stressful years. Once silks begin to desiccate, they lose their capacity for pollen tube growth and fertilization."

The full UN-L article is at this link:…

There are also other research and analysis article on this topic at other land grant university sites for more details.

Bryce Anderson can be reached at

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