The warm and dry spring has facilitated some of the earliest corn planting of all time in Minnesota, but early corn emergence increases the risk for frost damage.

Frost damage can occur even when air temperatures are in the mid-30s on calm nights, because the lack of wind allows colder temperatures to stay near the soil surface. In general, frost damage tends to be worse in low areas, on peat soils, near field edges and in fields with high levels of surface residue.

The first symptoms of frost damage to corn are dark and water-soaked leaves, which later dry and turn brown. Since the growing point of the corn plant remains below the soil until the fifth to sixth leaf-collar stage, frost prior to this stage typically does not kill the plant unless temperatures are low enough to freeze the upper part of the soil where the growing point is located.

To assess frost-damaged corn, dig up several plants from areas of the field with different soil types and elevation. Frost-damaged corn plants generally show new leaf growth a few days after the frost if their growing point was not damaged, so assessment of damaged fields should be delayed until three to five days after the frost.

To assess damaged plants, split the stems to examine the growing point and the tissue directly above the growing point. Healthy growing points will be firm and white to yellow in color. If the growing point is damaged, it will be watery and brown to orange in color, and the plant will not recover. If the plant tissue within a ½ in. above the growing point is damaged, the likelihood that the plant will recover is reduced.

Yield loss due to early season frost damage is influenced by the reduction in plant population and the severity of plant damage. In Minnesota, growers can expect yield losses of 5%, 12% and 24% when the final plant population is reduced to 28,000, 22,000 and 16,000 plants/acre, respectively. Growers should also consider the intensity of frost damage on survived plants. Recent University of Wisconsin research that simulated frost damage found that yield was reduced by 8% when all corn plants were cut off at the soil surface at the second leaf-collar stage, but that yield reductions were minimal when only half of the plants were cut off.

Before replanting, consider the yield potential of the existing crop, replanting costs and the yield potential of a replanted crop. Long-term research from southwest Minnesota shows that growers can expect about a 5% reduction in yield potential when corn is planted on May 15. If replanting, growers should carefully consider the length of the growing season that remains and select hybrids of appropriate maturity.

Detailed information on hybrid selection for late planting can be found at the U of M Extension website. For more educational resources on corn production in Minnesota, visit the Extension’s corn website.

Written by Jeff Coulter, corn agronomist with U of M Extension.