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Preemergence Freeze Injury in Corn
While early season frost injury is a fairly common occurrence for young corn plants in northern corn-growing areas, corn seedling death prior to emergence is relatively rare. When freezing conditions penetrate the soil enough to damage the coleoptile, mesocotyl, or the growing point, plant death can occur in seedlings that haven’t emerged from the soil. Sustained temperatures of 20 to 25 F or below are required for this type of penetration. This Field Facts discusses what to look for when freezing temperatures damage corn seedlings prior to emergence.
Coleoptile injury from freezing temperatures.
- Seedling Damage Symptoms
- Injury Diagnosis
- Post-freeze Crop Management
Seedling Damage Symptoms
Within the first 24 to 48 hours after the occurrence of freezing temperatures, corn plant tissue takes on a darkened appearance due to the destruction of cell membranes and the release of cell contents. The mesocotyl region just below the coleoptile also appears liquid-filled (photo below). Normal tissue color is initially maintained by plant parts not damaged.
Coleoptile injury from freezing temperatures.
Injury Diagnosis
Corn seedlings are very sensitive to freeze damage prior to emergence. Seedling survival depends on the stage of development, the severity of coleoptile damage, and whether the growing point was killed. Coleoptile and mesocotyl softening and browning indicates dying tissue. Even though the leaves within the coleoptile may have survived, the probability that they will emerge is low because the coleoptile is no longer able to protect them as they push toward the soil surface.
In most instances when the tips of the coleoptiles turn brown, they rupture prematurely. The plant response to this is often leafing out underground. In other cases the leaves become stuck in the coleoptile tip. If the growing point tissue is obviously damaged, plants will not recover. Corn plants die immediately when growing point tissue is frozen.
Leafing out underground.
(Photo courtesy of RL Nielsen, Purdue Univ.)
Corn plants not killed immediately may still succumb to various physical or biological factors that prevent recovery. Injured plants have reduced levels of resistance to secondary pathogens invading damaged tissues, and are more likely to sustain herbicide damage. Bacterial infections can contribute to additional plant death.
(Photo courtesy of RL Nielsen, Purdue Univ.)
For seedlings that have already emerged, or are just emerging above the soil surface, survival chances are somewhat higher since the growing point below the surface is protected by the whorl (assuming the growing point has not been frozen). The emerged leaves may die from the freezing temperatures, but others can grow in their place. However, even if the growing point appears healthy immediately after the frost, plants still may die. Cool weather after the frost can delay visible deterioration of damaged tissue on plants. Those plants not directly killed by the frost can succumb to the other factors described above.
Post-freeze Crop Management
- Wait 3 to 5 days with daily high temperatures above 70 F, then assess the number of plants per acre that are likely to emerge and produce healthy corn plants.
- If stand damage is substantial, assess the costs and benefits of leaving the stand vs. replanting.