Manage for Heat Stress to Protect Corn Yield

When it comes to corn, weather is always a gamble. Even your best planned field can find itself at odds with the thermometer. You can’t control the weather, but you can prepare to recognize the signs of heat stress and act accordingly.

Recognizing Heat Stress

The optimal temperature for corn is 86 F; heat stress on corn can occur when that number is surpassed. The combination of hot days and warm nights leads to additional plant stress. If daily temperatures routinely are at or exceed 95 F, corn is likely experiencing the negative impacts of being too hot.

As you check fields, keep an eye out for heat stress:

• Are your corn leaves dry and rolled up? This heat stress sign indicates that the plant is shrinking its surface area to reduce water loss.
• Do you see yellowing and burning along corn leaf edges? In severe drought, leaves may experience discoloration and appear gray or tan.

How Corn Responds to Heat

Corn is a sensitive plant, and an increase of a few degrees can have a large effect on productivity. As it warms up, transpiration increases. This is the rate at which water evaporates from leaves. In addition to this, photosynthesis slows down. The plant closes stomates, the openings along the surface of the leaf, to preserve water. This action cuts carbon dioxide intake which is needed for photosynthesis, resulting in slowed plant growth.

High heat also increases the need for water, making the demand for soil water more intense to avoid added water stress. Vapor pressure deficit occurs between the saturated leaves and air, which pulls more water out of the plant. This process places a greater demand on the soil to restore moisture.

Heat Stress Impacts Corn Yield

Despite all that the corn plant does to protect itself from high temperatures, potential yield loss could still happen. If your crop experiences prolonged heat, developmental processes that are needed for higher yields may be interrupted.

When the temperature hits 95 F, pollen and silks begin to dry up and leaf growth starts to slow. At 100 F, pollination will fail. At 113 F, net photosynthesis is reduced by 50-90%. Corn will react to stress the most during pollination and fertilization. Potential yield losses can reach 3-8% per day during this four-to-five-week window.

As the temperature rises, these are the main ways heat stress impacts corn yield:

• Kernel abortions take place when heat stress occurs at the same time as limited moisture. Kernels are usually aborted from the tip.
• Kernel set reduces if heat stress occurs within the four-to-five-week window surrounding silking.
• Ear size traits like diameter and length will shrink. Abnormalities like curved cobs or missing kernel rows can also occur.
• Reproductive stages that occur during heat stress can lower final yields due to pollen and silks drying out.
• Grain-fill time is shortened during high nighttime temperatures. The plant uses sugars meant for kernel fill for increased respiration instead.

Heat stress symptoms are intensified when they occur at the same time as drought. When this happens, the plant has a higher demand for soil moisture that goes unmet, further fueling the above symptoms.

Protect Yield During High Temperatures

It is safe to assume that heat stress will occur. If you see higher temperatures in the forecast, don’t fret. To help lower the impact of hot weather on yield potential, irrigate fields when extreme heat occurs.

Proactive management can also help protect future fields from intense heat stress symptoms. Focus on management strategies that conserve soil moisture like no-till or reduced-till to give crops the best chance during drought. High temperatures will impact corn plants less when there is adequate soil moisture. You can also choose hybrids that have strong stress tolerance and drought resistance traits.

Reducing other stressors like disease and pest threats will also help keep the plant hardier, including applying a fungicide like Miravis^® Neo or Trivapro^® fungicides to help offset some of the negative impacts of heat stress.