Corn Temperature Tolerance + Heat and Drought Stress in Corn

In 2023, drought-impacted 50% of the Midwest region.¹ Like any other crop, corn requires certain temperature and moisture levels to thrive and produce high yields. Heat stress and drought intensify damage to corn, but either condition may cause major crop injury all by itself.

📸: BASF internal photo/Featuring onion-leafed corn (the typical drought stress symptom in corn).

📸: @Ben Schonewille via Canva/Featuring a corn field that has suffered from severe heat stress for an extended period of time leading to plant death.

Corn can tolerate relatively high temperatures, with the ideal temperatures for corn ranging between 77 F and 91 F in daylight hours. If temperatures surpass 95 F, corn growth is slowed, though for short periods of time, corn can withstand temperatures up to 112 F.² It’s in periods of sustained heat and drought that growers need to pay particular attention. Learn about the yield-limiting effects of heat and drought stress on corn, especially at the critical pollination stage. Plus, learn what symptoms to look for if your corn is experiencing heat stress and drought conditions and how to manage drought-damaged corn fields.

When are corn plants most susceptible to stress?

The yield impact of heat stress on corn depends on the corn growth stage at which the stress is present. Corn is most susceptible to yield-reducing damage if heat and drought occur during the pollination (VT) to blister stage (R2). 

Yield impacts of drought stress in corn

When drought stress occurs for four or more consecutive days, growers can calculate yield loss per day using the following percentages: 

• VE to V12 (early vegetative growth): 1% to 3% loss per day
• V12 to VT (late vegetative growth): 2% to 5% loss per day
• R2 (pollination to blister): 3% to 9% loss per day
• R3 (milk): 3% to 6% loss per day
• R4 (dough): 3% to 5% loss per day
• R5 (dent): 2% to 4% loss per day
• R6 (physiological maturity): 0% loss per day³

Pollination is a critical stage when corn development (and subsequently, yield) can be affected by heat and drought stress. As tassels mature, the pollen they shed fertilizes the silk, resulting in kernel formation. Pollen shed occurs over a two-week period, and if temperatures are too high during this time, pollen and silk viability can be affected. 

Drought stress accelerates pollen shed. At the same time, it delays silk elongation, potentially causing pollen shed to occur before silk emergence, critically affecting pollination timing. Plus, once temperatures exceed 95 F (especially when paired with relatively low humidity) pollen is no longer viable and silks become desiccated and unreceptive to pollen, effectively impeding pollination. 

If hot temperatures remain at bay and successful pollination occurs, you are not out of the woods yet. To achieve proper grain fill, adequate moisture is especially key during R3 when corn begins to form its first small, watery kernels. Because heat stress hinders photosynthesis, if it occurs during the growth stages responsible for kernel determination, significant yield reduction can result.

How much water does corn need each day?

Corn needs approximately 0.3" of water per day during the early reproductive stages. Air temperature, humidity and cloud cover can impact the total amount of available daily soil moisture.⁴

Symptoms of heat stress and drought stress in corn

• Leaf rolling: The main indicator that corn is suffering from the effects of drought is leaf rolling; also called onion leafing. The earlier in the day leaf rolling occurs and the longer leaves remain rolled, the more stress the plant is experiencing and the more likely potential yield loss will follow.
• Leaf discoloration: In severe drought conditions, leaf tissue may also appear grayish or tan. 
• Reduced ear size or ear abnormalities: Drought and heat are considered stressors that may reduce ear diameter and ear length. Plus, these unfavorable conditions can cause abnormalities like banana ears (curvature of the cob) or zipper ears (missing kernel rows in ears). 
• Reduced kernel count: Drought and high temperatures can lead to poor or sporadic kernel set in the ear.

📸: CraneStation via Flickr/Featuring an image of a corn cob with sparse kernels.

• Ear tip back: Late-season moisture stress after pollination can cause kernels at the tip of the cob to die back.  

📸: BASF internal photo /Featuring an image of a corn cob with ear tip back.

How to manage heat and drought stress in corn

Corn plants are resilient and can successfully recover from drought damage. There are several ways to estimate corn yield. Conduct a shake test to find out if silks are still attached to the unfertilized kernels—silks will drop from fertilized kernels. You can also take a peek at cobs seven to 10 days after pollination (during the blister stage) to see how many kernels are developing. If pollination appears to be mostly successful, you can manage and harvest the field as normal.

However, if pollination appears to be inconsistent or unsuccessful due to drought conditions, consider a salvage harvest for silage. If corn leaves do not unroll at night when temperatures drop and 50% of leaves are dead or dying, you may want to harvest for silage to avoid total profit loss. This should be a last resort after you have allowed for potential recovery. Although the price of drought-damaged corn varies, Penn State Extension found that in some scenarios, drought-stunted corn with reduced ear count was still worth approximately 91% of normal silage. Drought-damaged corn without ears dropped to only 66% of normal corn silage.⁵

Typically, harvesting drought-damaged corn is still worthwhile, but in severely stressed fields the tasks associated with chopping including costs of fuel, labor and more may outweigh the profit. Understanding silage pricing can help you decide whether a salvage harvest is best for your situation.  

To lessen the impact of heat stress or drought on yield potential:

• Reduce other stressors to your crop, including common disease threats or pest-related stress.
• Consider irrigating in extreme heat conditions (especially if corn is already under other stressors that could delay silk emergence).
• If your area is susceptible to frequent drought and heat stress, look for drought-resistant hybrids.

Experts are available to help you make your decisions. Reach out to a nearby extension office agent or a professional like your regional BASF representative to make an informed choice.

📸: BASF employee/Featuring 7 DAT Right Treated with Priaxor® fungicide before Heat index of 90-100 degrees during June 9-11 (Treated June 8).

Learn more at Grow Smart^® Live:

Discover how to optimize your corn crop this season:

• Growing Corn: How and When to Plant Corn, Step by Step
• Corn Growth Stages: From Planting to Harvest

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Endnotes

1. "Drought Status Update for the Midwest U.S.”. Drought.gov, 19 Oct. 2023, www.drought.gov/drought-status-updates/drought-status-update-midwest-us-2023-10-19. Accessed 3 May 2024.
2. Thomison, Peter. "Hot, Dry Conditions Stressing Corn." Agronomic Crops Network, 2022, agcrops.osu.edu/newsletter/corn-newsletter/hot-dry-conditions-stressing-corn. Accessed 3 May 2024.
3. Quinn, Dan. "Heat Stress And Drought Considerations For Corn." Pest&Crop Newsletter, 21 June 2022, extension.entm.purdue.edu/newsletters/pestandcrop/article/heat-stress-and-drought-considerations-for-corn/. Accessed 3 May 2024.
4. Quinn, Dan. "Heat Stress And Drought Considerations For Corn.”

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