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Accessing Frost Damage On Corn And Soybeans

May 07, 2020

Planting corn early means having to deal with potential damaging frost events, but this is often accepted when conditions are otherwise suitable. However, according to Purdue University the threat of low temperatures in late May or early June also raises the specter of frost or low temperature damage to young corn plants, regardless of the planting date. Early morning temperatures in the 30s in addition to clear calm conditions overnight certainly are favorable for frost formation on any exposed surfaces, including leaves of young corn plants. This means temperatures do not need to drop to 32F or cooler in order for frost to form.

When significant frost develops on young corn plants, it is easy to jump to the conclusion that significant plant mortality will soon follow. However, frost by itself is not a guaranteed "kiss of death" for young corn plants. What is more important is whether the temperature that accompanied the frost event was lethal or not. Most agronomists agree that "lethally cold" temperatures for young corn are those that dip to 28F or lower for 1 to 2 hours.

The effect of frost on young corn when it is paired with temperatures no lower than about 30F is primarily damage and death of the exposed above ground leaf tissue. As long as the growing point is protected below the soil surface, the injured plant usually recovers from the effects of the superficial leaf damage.

Within 3 to 5 days of the frost event (more quickly with warm temperatures, more slowly if cool), elongation of the undamaged leaf tissue in the whorl will become evident. As long as the recovery is vigorous, stand establishment should be not be affected.

Plant appearance following damage by lethal cold temperatures (typically 28F or lower for a few hours) may initially be similar to that due to "simple" frost damage. The difference is that there will be no subsequent elongation or "recovery" of leaf tissue from the whorl like you would see in the days following "simple" frost damage to leaves. Inspection of the growing point area (by slicing down middle of stem, through the crown of the young plant) will eventually reveal discolored, soft or mushy tissue as a consequence of the lethally low temperatures.

The bottom line for diagnosing the severity of frost or low temperature injury to corn is that you typically need to wait three to five days after the cold weather event before you can accurately assess the extent of damage or recovery. Injury to the crop can look very serious the day after the event or even two days after the event, but recovery is likely if there is no injury to the growing points of the plants in questions.

Soybeans can also be damaged by cool weather, but this is less likely to happen. Click below for more information about spring frost damage to soybeans from the University of Minnesota:

https://extension.umn.edu/growing-soybean/spring-frost

Additional information from Winfield United:

https://www.centrasota.com/CTRA/media/Files/Early-Season-Frost.pdf
 
7 hrs post-frost
 
 12 hrs post-frost

60 hrs post-frost


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