This past weekend significant areas of northern Wisconsin were affected by frost with temperatures below 28 F. Most corn has either not emerged or is just starting to emerge. The key management practice here will be patience. It will take some time to determine if corn was damaged by this frost.
Corn plants will not be killed by frost unless temperatures get cold enough to kill the growing point that is 3/4 of an inch below the soil surface. So corn that has not emerged typically is well insulated from frost damage. So corn that has not emerged typically is well insulated from frost damage.
Frost should not be a problem with corn until the growing point moves above-ground around V5 to V6. Farmers and agronomists usually do not worry about frost at these early stages of development. Early frost can have an impact on grain yield, but the trade-off between planting date impact on yield is greater than for frost damage impact on yield. Delayed planting further impacts profitability due to greater moisture and consequential drying costs.
Symptoms of frost damage will start to show up about 1 to 2 days after a frost. Symptoms are water soaked leaves that eventually turn brown. After 3 to 4 days watch for new green leaves emerging n the whorl. If new leaves are not emerging check the growing point for discoloration. Any deviation from a white, cream or light yellow color indicates that the growing point is killed.
To measure the impact of early defoliation on corn grain yield corn plants were clipped with a scissors. Clipping treatments were applied at V2, V4 and V6. Plants in the control treatment were not clipped. In another treatment, all plants in the plot were clipped. In another set of treatments, half of the plants were clipped in 2-, 4-, and 8-plant patterns. For example in the 2-plant pattern, the first 2 plants in the row were not clipped, the next 2 plants were clipped at ground level, the next 2 plants were not clipped, and so on.
Although these treatments do not fully simulate the frost damage, they do provide some guidance on what a frost might do that completely defoliates the plant without killing it. Figure 1 describes the impact of complete defoliation on corn grain yield at the V2 stage of development. When all plants were clipped, grain yield decreased 17 bu/A from 210 to 193 bu/A (8%). When half of the plants were clipped in various patterns, grain yield was not affected; the trend was a decrease of 8 to 9 bu/A (4%).
These data indicate that frost early in development has relatively little impact on corn grain yield. If all of the leaves are removed from every plant in the field at the V2 stage of development and plants are not killed, then the expectation is that grain yield would decrease up to 8%. If the recent frosts were hard enough to kill plants then use the publication UWEX 3353 for guidance on whether or not to keep a stand and what to look for when assessing plant health.