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Did Your Corn Get Nipped by Frost? Here's What to Look For

Tuesday morning may be a chilly one for a lot of farmers in the northern Plains and Midwest. Spotty snowshowers early on Monday are expected to unfurl into widespread temperatures in North Dakota down into the mid- to upper-20s, with subfreezing temperatures reaching as far south as Nebraska.

But at the same time, a lot of the nation's corn crop is in the ground, including 70% of North Dakota's crop, more than 20% of the normal pace, according to Monday's USDA-NASS Crop Progress report.

That's not the best combination in the world.

If you're in a potentially affected area and anticipate frost or freezing temperatures tonight, you may be eager to drag the winter coat back out of the closet and check your fields after the sun rises and reveals what sort of damage a late-season Jack Frost may have inflicted. If so, make the most of your time to help make any follow-up decisions as quickly and easily as you can.

First, start with the fields with the most potential for frost damage, says University of Minnesota Extension corn agronomist Jeff Coulter.

"In general, frost damage tends to be worse in low areas where cold dense air settles, near field edges where vegetation reduces the potential for heat transfer from the soil to the air above, and in fields where high levels of surface residue coverage limit heat transfer from soil. In addition, fields that were recently row-cultivated prior to cold temperatures are more susceptible to frost injury, as tillage dries the surface soil, thereby reducing the amount of heat and moisture that can be transferred between the soil and air," he says.

Look for leaves that are wet to the touch or, depending on how quickly you get into the field, dry leaves that have begun to take a brownish hue. Frost damage doesn't always mean fatality for young corn plants, but knowing how much yield potential you may have lost can help with decisions down the road.

"Symptoms of frost-injury to corn are initially discolored 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. 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 a frost. Buggy-whipped plants generally break free and recover following new vegetative growth, and this is influenced by the air temperatures, wind, and the size of the plants when damaged," Coulter says. "To determine whether frost-damaged corn will survive, 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 plant tissue within 0.5 inches above the growing point is damaged, it will be watery and orange to brown in color, and the plant will not likely recover. In general, crop recovery tends to be greatest when frost occurs before the third leaf-collar stage or when only a limited amount of leaf area is damaged after the third leaf-collar stage, since recovery is influenced in part by the amount of energy reserves in the seed and leaf area for growth."

Though you can get a feel for young plant damage visually this early on, the best guess will be to watch for mortalities later on and extrapolate those losses to a seed count, then take that number to an overall seed population and resulting yield potential. In other words, if you planted 25,000 seeds an acre and lost 10% of them, you should be able to get an idea for what yields your field can still make.

"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 per acre, respectively. In addition to reductions in plant population, growers should consider the severity of frost damage on remaining plants," Coulter says. "Research from Wisconsin 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. In addition to yield losses, frost-damaged plants may reach maturity a few days later than normal."

If the frost is bad enough, you may wind up having to replant, obviously. But, how bad is bad enough?

"Before replanting, growers should consider the yield potential of the existing crop, replanting costs, and the yield potential of a replanted crop. Replant costs including time, fuel, seed costs, and penalties associated with hybrid selection when the best genetics are no longer available. Yield potential of a replanted crop will also be influenced by planting date," Coulter says. "Corn planting date studies show that on average, grain yield was reduced by 5% and 18% when corn planting was delayed until May 15 and May 30, respectively. If replanting, growers should also consider the length of the growing season that remains and select hybrids of appropriate maturity."

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