Crop Comments: Managing Corn Planting Timing to Dodge Future Weather ‘Bullets’

Corn was originally a tropical grass from high elevation areas of central Mexico (about 7,400 feet above sea level). Today, corn still prefers conditions typical of that area – warm daytime temperatures and cool nights. Areas that consistently produce high corn yields share some significant characteristics. These areas – like central Chile, the west slope of Colorado, etc. – are usually very bright, clear, high light intensity areas with cool nights.

In “How Extended High Heat Disrupts Corn Pollination,” Tom Hoegemeyer, Ph.D., University of Nebraska- Lincoln, wrote, “Corn maximizes its growth rate at 86º F. Days with temperatures hotter than that cause stress. In the high yield areas, cool night temperatures – at or below 50º – reduce respiration rates and preserve plant sugars, which can be used for growth or reproduction or stored for yield. These are optimum conditions for corn, and interestingly, are fairly typical for areas around central Mexico where corn is native.”

He stressed that last year, as well as other recent years, in the prairie states and the Corn Belt conditions have been dramatically less than optimal. 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. Daytime temperatures have consistently stayed in the upper 90s to low 100s in the Midwest. During 2025, in the Northeast’s corn growing areas, we experienced prolonged stretches of 90º peaks.

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.

Further quoting Hoegemeyer, “Corn is a ‘C-4 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,” Hoegemeyer said. “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.”

He emphasized that 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.

Even with adequate moisture and timely silking, heat alone can desiccate silks so that they become non-receptive to pollen. While this is a bigger problem when humidity is low, it apparently happens in moister years, especially on hybrids that silk quite early (relative to pollen shed). Even with dew points in the 70s, when temperatures reach the high 90s, the heat can still desiccate silks and reduce silk fertility.

Hoegemeyer noted that excess heat (over 95º) also depresses pollen production and viability. Continuous heat over several days before and during pollen shed results in only a fraction of normal pollen being formed, probably because of the reduced sugar available.

In addition, heat reduces the period of pollen viability to a couple hours (or even less). While there is normally a surplus of pollen, heat can reduce the fertility and amount available for fertilization of silks. Prolonged exposure to high temperatures reduced the volume of pollen shed and dramatically reduced its viability.

For each kernel of grain, one silk needs to be fertilized by one pollen grain. According to Elwin Taylor, Iowa State University climatologist, and Roger Elmore, ISU crop production agronomist, “we are seeing an oscillating weather pattern where above-normal temperatures east of the Continental Divide are likely to persist for up to six weeks. In the past, such patterns have been consistently associated with below trend corn yields for the U.S.”

Taylor pointed out that the treacherous aspect of this pattern is that extended periods of heat tend to diminish yields even more. When soil moisture is sufficient, one day of 95º – 98º has little or no impact on yields. However, after the fourth consecutive day there tends to be a 1% loss in yield for each day above that temperature. After the fifth or sixth day, there tends to be even greater potential for yield loss. While it’s difficult to make yield loss predictions from heat and drought stress in any year, the stress adds up and takes a toll on the crop.

Alex Lindsey, Ph.D., corn physiologist at Ohio State, stressed that corn-growing conditions in the Northeast and Midwest are experiencing warmer temperatures that have led to earlier frost-free dates, with temperatures above freezing during the daytime yet still cold (lower than 50º). With this type of cold stress, “damage occurs within 24 – 28 hours of planting. The exact temperature range isn’t well known. It occurs when temperatures are below 40º. Cold injury, after emergence, happens when the seed is exposed to temperatures below 46º for extended time. It’s not clear what brief exposure periods would do.”

He said the best way to remedy cold temps is to “stagger planting dates. Planting all at once gambles at stakes far too high if a cold snap kills the seeds. It’s vital to avoid temperatures that are 46º or below during emergence.”

I’ll add that the practice of staggering corn planting dates increases the likelihood of silking and pollinating functions dodging injury caused by prolonged heat snaps a few weeks later in the growing season.

by Paris Reidhead