By R.L. (Bob) Nielson
Agronomy Dept., Purdue Univ.

Early morning temperatures in the low to mid-30s (F) coupled with clear calm conditions overnight certainly are favorable for frost formation on exposed surfaces, including leaves of young corn plants. The risk of a late spring frost is one of the downsides to planting corn earlier than normal, but is one growers often accept when early spring field conditions are otherwise suitable for planting.

When significant frost develops on young corn, it is tempting to jump to the conclusion that significant plant mortality will be a natural consequence. However, frost by itself is not a guaranteed "kiss of death" for young corn. 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 some minimum length of time.

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

Within a number of 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, subsequent stand establishment should be not be affected.

The bottom line for diagnosing the severity of frost or low temperature injury to corn is that you generally need to wait three to five days after the 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 affected plants.

SOURCE: Purdue University.