The cold snap on May 2nd and 3rd affected some early planted corn and soybean fields this spring. At the Western Agricultural Research Station, our corn and soybean planted on April 14th experienced cold temperatures. Emerged soybean and corn were subjected to frost damage with air temperatures lingering around 30-32℉ for about five hours, with the low reaching 29ºF.
How did corn survive the freezing temperatures?
Corn at the Western Agricultural Research Station was at the VE to V2 stage when temperatures dropped to freezing. Twenty-four hours after the freezing event, over 70% of the seedlings showed visual chilling injury, mostly appearing as pale, yellowed leaves (Figure 1a). When we dug up a few of these pale plants, the mesocotyl and crown were still white in color, showing the signs of a healthy seedling (Figure 1b). The growing point on corn stays below ground until the V6 stage. During the freeze event, the lowest soil temperatures in our plots ranged between 39℉ and 42℉ across both shallow (1-inch) and deeper (3-inch) depths, indicating the growing points did not experience freezing temperatures. If ice had formed in the aboveground tissues, it did not appear to reach the growing point belowground.
Figure 1. (1a) April 14th planted corn 24 hours after the freeze (May 4th). (1b) Uprooted corn showing a healthy mesocotyl and crown.
We staked a few damaged plants and assessed corn seedlings one week after the freezing event to see if there was regrowth or death of the growing point. One week after the freezing event, 100% of staked corn seedlings showed successful regrowth (Figure 2). New tissue had some leaf injury symptoms, but in this study, we had minimal buggywhipping, and new shoots seemed to be emerging with minimal issues.
Figure 2. Freeze-damaged corn seedlings showing new regrowth six days after the cold snap that occurred on May 2nd and 3rd.
At the plant-level, corn is successfully recovering from the freeze damage, but there could be yield penalties associated with these stressful conditions early in the growing season. In 2024, corn experienced flood damage followed by freeze damage, which resulted in a small yield penalty (Figure 3) compared to later planting dates where plants did not experience those conditions.
Figure 3. Slight yield penalty when corn was planted on March 25, 2024 after experiencing a flood event followed by a freeze event at the Western Agricultural Research Station.
How did the soybean survive the freezing temperatures?
We followed the same procedure for soybeans to see how they performed after experiencing freezing temperatures. Emerged soybean seedlings were in the VE to VC stage when temperatures dropped to freezing (though some soybeans had not yet emerged). Twenty-four hours after the freeze, the damaged soybean seedlings showed chilling injury symptoms such as yellow-to-brown, water-soaked cotyledons and a water-soaked, shriveled hypocotyl (Figure 4). Unlike corn, a soybean’s growing point is above ground as soon as it emerges, making it vulnerable to freeze damage.
Figure 4. April 14th planted soybeans 24 hours after the freeze event (May 4th).
When we checked 24 hours after the freeze event, about 29% of the soybeans that emerged before the cold snap showed clear signs of frost damage. We staked the visibly damaged seedlings to see if they could recover. Unlike corn, one week later, nearly all the affected seedlings had died (Figure 5). With soybeans, emergence continued after the cold snap. When we collected stand counts on May 14th (2 weeks after the cold snap), 30% of the total stand count consisted of plants that emerged after the cold temperatures occurred. Because the lowest soil temperatures across all planting depths stayed between 37℉ and 41℉, the seeds still below ground were protected from the freezing air temperatures and successfully overcame the cold snap event.
Figure 5. Tracked soybean seedlings one week after the freeze event, showing severe damage and plant death.
At the plant level, soybeans are susceptible to freeze damage because their growing point is above ground at emergence. However, at the field level, soybean is more resilient compared to corn. At the Western Agricultural Research Station, soybean plants were damaged by a freeze event in 2024, which resulted in low plant populations (averaging 50,000 plants per acre). Although plant population was low, it yielded statistically the same (average of 74 bushels per acre) as soybean planted in mid-May that had plant populations closer to 100,000 plants per acre (average of 63 to 73 bushels per acre).
Next steps for these field trials
This research trial where we have been tracking plant survival also contains a planting depth component, and we are still working through understanding if and how planting depth treatments played a role in the damage and survival of soybeans (or corn). We will continue to monitor plant stands and their development this season, and we will track some of these plants all the way to yield. Improving stands early-season can help leverage yield gains from early planting (when stress is not present), and this work should help determine how planting depth affects early-season emergence (and survival from cold snaps around planting/emergence timing).
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