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Don’t Sweat Early Frost Injury to Corn

Upper Midwestern farmers have endured below- or near-freezing air temperatures the past few days. As a result, frost-injured corn in some regions of Minnesota has surfaced. The telltale signs of frost damage are initially discolored water-soaked leaves, which later dry and turn brown. 

So what now? Here’s what to look for and consider from Jeff Coulter, University of Minnesota Extension corn specialist. 

The Good News

It’s unlikely the damage will be permanent, thanks to the location of corn’s growing point at this time of year. In Minnesota, it’s currently about 0.75 inches below the soil surface. It will remain below the soil until the five leaf- or six leaf-collar stage. Frost prior to this point typically does not kill corn, unless prolonged cold temperatures freeze the upper part of the soil where the growing point is located. 

Frost-damaged corn generally shows new leaf growth a few days after a frost if the growing point was not damaged. Therefore, delay assessment of damaged fields until at least three days after a frost, advises Coulter. 

Larger corn plants damaged by frost can resemble buggy whips, as new vegetative growth tries to break free of dead tissue. Buggy-whipped plants generally recover, with a faster recovery rate for smaller plants and when warm and windy conditions occur after a frost.

To determine frost-damaged corn survival, Coulter says to dig up plants and split 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 or tissue within 0.5 inch above the growing point is damaged, it will be water-soaked and orange to brown, and recovery is unlikely. Corn recovery is greatest when frost occurs before the three leaf-collar stage or when only a limited amount of leaf area is damaged after the three leaf-collar stage. 

How much can frost reduce yields? 

Plant population reduction and plant damage severity influences yield loss due to early-season frost injury, says Coulter. In Minnesota, reductions in corn grain yield of around 5%, 12%, and 24% are expected when the plant population is reduced to 28,000, 22,000, and 16,000 plants per acre, respectively.

The severity of frost damage on surviving plants also should be assessed. Early-season frost injury tends to delay corn maturity by a few days in the fall. 

Replanting Considerations

Before replanting, consider the existing crop’s yield potential, replanting costs, and the replanted crop’s yield potential, says Coulter. Replant costs including time, fuel, seed costs, and penalties associated with hybrid selection if the best genetics are no longer available.

In Minnesota, corn planted on May 20 to 25 yields about 87% to 95% of that planted in late April to early May. If replanting, consider the length of the remaining growing season, and select hybrids of appropriate maturity. 

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