The potential for late spring freeze or frost damage to corn exists on an annual basis. This Field Facts discusses what to look for after a freeze as well as factors that will affect management after initial injury.
Symptoms of Frost Damage in Corn
Various symptoms help growers to identify when low temperatures have produced frost damage to corn. These symptoms include the following:
Darkening of leaves - Within the first 24 hours after the frost, corn plants will take on a darkened, almost black appearance due to the destruction of cell membranes and the release of cell contents from damaged corn leaves.
Plants turn brown - When plant cells have been destroyed, the damaged leaf portions will dry up and begin to turn brown within a day after a frost. Some lower plant parts (pseudo stem) may remain intact and will stay green.
Diagnosing Frost Injury
When freezing temperatures injure corn plants in a field some plants may survive and recover, while other plants will die. One of the first steps in diagnosing frost injury is to check the health of the internal growing point. Plants can be split vertically and the growing point region inspected visually for damage. If the growing point tissue is obviously damaged, plants will not recover. Corn plants die immediately when growing point tissue is frozen. Corn plants not killed immediately may still succumb to various physical or biological factors that prevent recovery, including:
Plant starvation - Leaf loss due to frost injury reduces photosynthetic area available to produce carbohydrates for new plant growth and recovery.
Plant disease - Injured plants have reduced levels of resistance to secondary pathogens invading damaged tissues.
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.
Assessing Recovery Potential – Growing Point Above Ground
Many of the considerations are the same as for earlier stages. It is important to evaluate the health of the growing point and not to assume that plants will recover, even if the growing point was not damaged directly by the frost. Amount of green tissue remaining, growing conditions during re-growth, and whether frost damage involved single or repeated episodes are important factors that will influence recovery potential.
Similar to earlier stages, the most reliable way to determine frost impact is to wait until after 3 to 5 days with daily high temperatures above 70°F and check for evidence of new growth. Remove dead whorls and look for erect, lime green leaf growth inside the corn plant. Another sign of active growth is a "rippled" leaf effect within the whorl when the plant is cut lengthwise. The "rippled" leaves indicate that new growth occurring after the frost is backing up behind the damaged, knotted whorl.
Post-Frost Management Options
When growers experience frost damage in a corn field, they are faced with several management options. They may choose to do nothing, leaving the field as it is and allowing plants to recover. Another option if still early in the growing season is to replant the field to corn or another crop. A final management choice is to clip corn plants after frost to remove the dead and decaying tissue found above the growing point. This is usually only an option when the plants are at the V5 toV6 or later stages when the damage occurs. It will be difficult to clip smaller plants with field-sized clipping equipment.
Clipping frozen corn plants to remove dead tissue has been studied by several researchers. While results are somewhat variable, the general conclusion is that clipping does not enhance yield in most situations, and often further reduces yield compared to not clipping damaged plants.