Crop Comments: Stagger corn planting times to minimize empty kernels

According to Dan Quinn, Purdue University agronomist, examining corn ears from your fields helps estimate what yield might be. Examining corn ears prior to harvest helps growers visualize how the corn plant was impacted by different factors throughout the growing season, and why their yields may be less than hoped for.

With Quinn’s help, I was able to get answers to the questions “Tip die-back in corn: what is it, and what does it mean?”

One of the biggest concerns observed on corn ears examined in 2025 was tip dieback – corn ears did not fill kernels from the base of the ear all the way to its tip. Ear tips showed missing and/or incomplete kernels. There are two main reasons for tip die-back: poor pollination, causing the absence of kernel formation; and kernel abortion.

The silks emerging last from an ear during pollination, and the kernels that fill last during grain fill, are on the ear tip. Any significant stresses exhibited shortly before, during or shortly afterward pollination negatively impact these “youngest” kernels. If many of your corn ears exhibit tip die-back, examining ear tips closely helps one understand the cause of the problem.

According to Quinn, poor pollination occurs when stressful conditions hit a few weeks prior to and during pollination (e.g., silk and tassel emergence). For example, drought conditions can delay silk emergence and cause poor teamwork (for want of a better term) between pollen drop and silk emergence. Since the last emerging silks are located at the ear tip, pollen drop (which occurs only for seven to 10 days) can be completed prior to silk emergence, thus causing the potential kernels at the ear tip to remain unpollinated.

In contrast to missing tip kernels caused by poor pollination, kernel abortion is identified by shrunken and shriveled kernels on the ear tip. Kernel abortion is mainly caused by stresses reducing plant photosynthetic output (e.g., drought, hail damage, nutrient deficiencies, foliar disease) during the first several weeks following pollination and through the R3 (milk) growth stage. Consecutive days of cloudy weather reduce plant photosynthesis enough to cause kernel abortion.

Any plant stresses limiting photosynthetically active leaf area of the corn plant can cause tip fill problems.

Last August, ag journalist Leslie Sattler, writing for the “The Cool Down” (thecooldown.com), explained that too many farmers overlooked dangers posed by Canadian wildfires. Nearly 14 million acres of forest in Canada had burned thus far in 2025, double the typical amount for this period. The smoke traveled hundreds of miles south, carried by wind patterns and jet streams into America’s Heartland.

Sattler stressed that the timing couldn’t be worse for Midwest farmers. Corn crops were pollinating; soybeans were developing canopies. Both species need strong sunlight for photosynthesis for optimum yields. She tapped into the wisdom of Mark Jeschke, Ph.D., a commercial plant scientist.

“We know there are ways that smoke can affect crops… negatively impacting crop yield,” said Jeschke, agronomy manager at Iowa-based Pioneer Seed Co.

Jeschke and Quinn stress that Canadian wildfires aren’t going away, pointing out that over the past 40 years, U.S. wildfires have increased four-fold to over eight million acres annually. As smoky days become more common in agricultural regions, corn and soybean producers increasingly ask how wildfire smoke affects crop productivity. Jeschke explained that the relationship between wildfire smoke and crop growth is complex, with both positive and negative effects on photosynthesis.

Three factors determine how smoke influences photosynthesis. First is reduced sunlight intensity. Smoke reflects a portion of incoming sunlight, reducing the amount of light available to plants. Because plants need sunlight to carry out photosynthesis, any reduction in light can harm crop productivity.

The second factor was increased sunlight diffusion. In this scenario, wildfire smoke can significantly increase the diffuse fraction of photosynthetically active radiation. This benefits plants by increasing light use efficiency, as well as the availability of light to lower canopy leaves.

The third factor is ground-level ozone (O3). Elevated O3 often greatly reduces crop yields. Dicot species, such as soybeans, appear more susceptible to yield reduction from O3 than most monocot species, like corn.

Crops depend on sunlight to drive photosynthesis and achieve high yields, and a reduction in solar radiation, especially during the critical grain-filling period, can hurt. Quoting Jeschke: “The risk of yield loss and reduced stalk health from wildfire smoke is likely greater when smoke imposes an additional stress on a crop already suffering from other stresses, like disease or drought. Reductions in yield can be dramatic. Studies that have included shade treatments that reduce light by 50% or more during grain fill have seen corn yield drop by more than half.”

In addition to direct effects on corn yield, reduced solar radiation also affects stalk quality and standability. Upon successful pollination, ear development places a great demand on the plant for carbs. When the demands of the developing kernels exceed the carbohydrate supply produced by leaves, stalk and root storage reserves are utilized. Environmental stresses which decrease the amount of photosynthesized material can force plants to extract even greater percentages of stalk carbohydrates.

As carbs stored in the roots and stalk are mobilized to the ear, these donating structures decline, soon losing their resistance to soil-borne pathogens. Instances of severe stalk rot and lodging are common with prolonged periods of low solar radiation during grain fill.

Jeschke concluded, “It’s a virtual certainty that wildfire smoke in the atmosphere will continue to increase in frequency and concentration for the foreseeable future, making it important to understand how crop growth and productivity might suffer.”

Interestingly, organic crops may fare better in wildfire smoke than conventional crops. This idea surfaces more frequently as wildfire smoke becomes more common. In the favor of organic practices (here meaning sustainable and chemical-free), national standards mandate that farmers maximize carbon retention in soil. Keeping as much carbon as possible in soil goes a long way toward combating climate change directly (and wildfire smoke indirectly).

There are four basic categories for inputs required for successful crop production: solar radiation, moisture, warmth (soil and air) and soil nutrients. All are equally important, because if any one is seriously limiting, crop production plummets. The input category threatened most by wildfire smoke is solar radiation.

by Paris Reidhead