3 May 2023
URL: http://www.kingcorn.org/news/timeless/EarlyPlantedCornColdWthr.html
Early-Planted Corn & Cold Weather
R.L. (Bob) Nielsen
Professor Emeritus & Retired Extension Corn Specialist
Agronomy Dept., Purdue Univ.
West Lafayette, IN 47907-2054
Email address: rnielsen at purdue.edu
Twitter: @PurdueCornGuy
- Early planted corn always involves the risk of cold weather in the weeks after planting.
- Imbibitional chilling injury occurs within a day or two of planting.
- Chilling injury after germination can cause delayed or failed emergence.
- Slow plant development increases risk of injury by diseases or insects.
he talk among some of the regulars down at the Chat 'n Chew Cafe is that some of their neighbors who were feeling so smug a week ago about having planted so much corn are now feeling less certain of the wisdom of their actions in light of the recent cold temperatures and, in some cases, frost. Should they be concerned about the health of their newly planted and, in a few cases, newly emerged crops? Well, we'll know for certain come harvest time. But in the mean time, we can talk about possibilities.
Newly Planted Corn
One of the risks that newly planted corn faces is that of imbibitional chilling injury caused by exposure of the kernels to cold soil temperatures during the initial 24 to 36 hours after seeding, when the kernels imbibe water and begin the germination process. In response to the imbibition of water, kernels naturally swell or expand. If the cell tissues of the kernel are too cold, they become less elastic and may rupture during the swelling process. Symptoms of imbibitional chilling injury include swollen kernels that fail to germinate or arrested growth of the radicle root and/or coleoptile following the start of germination. Alternatively, chilling injury that occurs during the emergence process can cause stunting or death of the seminal root system, deformed elongation of the mesocotyl (the so-called "corkscrew" symptom) and either delayed emergence or complete failure of emergence (i.e., leafing out underground). The net result of either type of chilling injury to corn is a combination of stunted plant development and outright loss of stand.
It is not clear how low soil temperatures need to be for imbibitional chilling or subsequent chilling injury to occur. Some sources simply infer temperatures less than 50F (10C). Others suggest the threshold soil temperature is 41F (5C). Daily minimum soil temperatures at the 4-inch depth (typical depth for National Weather Service measurements) have certainly dropped into the mid- to high-40's (F) in recent days, with some growers reporting temperatures as low as 40F at seed depth.
Newly Emerged Corn
Damage from exposure of above-ground plant tissue to frost can range from minor leaf injury to complete death of all exposed leaf tissue. That's the bad news. The good news is that the all-important growing point region of a young corn plant remains below the soil surface, safe from exposure to frost, until the V4 to V6 stages of development. That means that the above-ground plant tissue you see in fields younger than about V4 is composed primarily of leaves and rolled up leaf tissue in the whorl, but does not include stalk tissue or the growing point. As long as temperatures are not lethally cold, "simple" frost injury usually does not literally kill such young corn plants. Damaged plants will begin to show recovery from the whorl within 5 to 7 days, depending on temperatures following the frost event.
Disclaimer: Repeated frost events that re-inflict damage to recovering corn plants can cause permanent stunting or death.
When folks worry about the effects of cold weather on corn, they often fail to distinguish between simple frost events and lethal cold temperatures. Frost can occur at temperatures easily up to the high 30's F, but lethal cold temperatures for corn are generally thought to be 28F (-2C) or colder. Such cold temperatures may "penetrate" the upper inch of soil near the growing point region of corn seedlings, especially if soils are excessively dry and free from surface residue.
In situations where temperatures have simply been sub-optimal (i.e., less than 50F), but without frost, the direct effect on the corn crop is simply slow development. Once planted, it requires 115-120 GDD (Fahrenheit) for the crop to emerge. Once emerged, it requires about 80-85 GDD to progress from one leaf stage to another up to about leaf stage V10 (10 visible leaf collars). After V10, leaf stage progresses at about 50-55 GDD per stage. The main risk associated with slow plant development is that many protective seed treatments (fungicide, insecticide) dissipate after about 2 to 3 weeks, leaving slow-developing young plants vulnerable to soil-borne diseases and insects, and thus increasing the risk for additional stunted plants or stand loss.
To put that into perspective for the 2023 planting season to date, total accumulation of soil-temperature based GDD (F) between 16-Apr-2023 and 2-May-2023 ranges from about 50 GDD in the northern parts of the state to about 70 GDD in the southern parts of the state. That explains why the May 2nd USDA-NASS report estimated only 1% of Indiana's corn crop was emerged even though 20% of the state's corn crop was estimated to have been planted.
Bottom Line
Only time will tell whether the cold temperatures of recent weeks will cause permanent damage or death of early-planted corn around the state. Some early-planted fields will likely require some replanting because of poor stands. Come October, we will know for certain whether this year's early planting risk takers will have "won the game" or not.
Related Reading
Nielsen, RL (Bob). 2001. Symptoms of Low Temperature Injury to Corn and Soybean. Corny News Network, Purdue Univ. http://www.kingcorn.org/news/articles.01/Frost_Corn_Soy-0418_Gallery.html [URL accessed May 2023].
Nielsen, RL (Bob). 2019. Determining Corn Leaf Stages. Corny News Network, Purdue Univ. http://www.kingcorn.org/news/timeless/VStageMethods.html [URL accessed May 2023].
Nielsen, RL (Bob). 2019. Growing Points of Interest. Corny News Network, Purdue Univ. http://www.kingcorn.org/news/timeless/GrowingPoints.html [URL accessed May 2023].
Nielsen, RL (Bob). 2019. Visual Indicators of Germination in Corn. Corny News Network, Purdue Univ. http://www.kingcorn.org/news/timeless/GerminationEvents.html [URL accessed May 2023].
Nielsen, RL (Bob). 2020. Assessing Frost / Cold Temperature Injury to Young Corn. Corny News Network, Purdue Univ. http://www.kingcorn.org/news/timeless/FrostedCorn.html [URL accessed May 2023].
Nielsen, RL (Bob). 2020. Cold Soils & Risk of Imbibitional Chilling Injury in Corn. Corny News Network, Purdue Univ. http://www.kingcorn.org/news/timeless/ImbibitionalChilling.html [URL accessed May 2023].
Nielsen, RL (Bob). 2020. Heat Unit Concepts Related to Corn Development. Corny News Network, Purdue Univ. http://www.kingcorn.org/news/timeless/HeatUnits.html [URL accessed May 2023].
Nielsen, RL (Bob). 2020. Requirements for Uniform Germination & Emergence of Corn. Corny News Network, Purdue Univ. http://www.kingcorn.org/news/timeless/GermEmergReq.html [URL accessed May 2023].
Nielsen, RL (Bob). 2020. The Emergence Process in Corn. Corny News Network, Purdue Univ. http://www.kingcorn.org/news/timeless/Emergence.html [URL accessed May 2023].
Nielsen, RL (Bob). 2022. Emergence Problems in Corn. Corny News Network, Purdue Univ. online at http://www.kingcorn.org/news/timeless/EmergenceFailure.html.html [URL accessed May 2023].
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