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Is your early-planted corn at risk?

The sun's out, the temperature's rising -- perfect weather for planting corn. But, you may have already planted some of your acres when conditions were less-than-ideal. Even if you did, and you're worried about how that seed you planted when soils were cool and wet, you may not be in as bad of shape as you thought, says one expert.

"Although it’s too early to determine how corn already planted will respond to recent weather, the effects of the low temperatures on corn survival will probably be negligible for the most part," says Ohio State University Extension corn production specialist Peter Thomison. "In past years, we have observed that early planted corn that was in the process of germinating or as far along as the V1 stage (one leaf collar visible) survived freezing soil temperatures in April with little impact on crop performance or plant stand."

Chances are good that your newly planted corn kernels hadn't emerged to the point where the growing point was exposed to the coolest temperatures, some of which dipped to or south of the freezing point last weekend. That is the difference between a crop that's nipped by frost or freeze, or one that sticks it out through the cold snap.

"Agronomists generally downplay the impact of low temperature injury in corn because the growing point is at or below the soil surface until V6 (6 leaf collars visible), and thereby relatively safe from freezing air temperatures," Thomison says in a university report. "Moreover, the cell contents of corn plants can sometimes act as an 'antifreeze' to allow temperatures to drop below 32 degrees F before tissue freezes, but injury to corn is often fatal when temperatures drop to 28 degrees F or lower for even a few minutes."

Freezing temperatures like these are made "far more serious" when accompanied by precipitation, worst when it's of the frozen variety, Thomison says. But, even if it's not frozen, rain can cause serious damage to sprouting kernel in the soil via imbibitional chilling, says University of Nebraska Extension cropping systems specialist Greg Kruger.

"When corn seeds imbibe water, the cell membranes will stretch and cells will expand. When a damaged cell membrane is rehydrated, it may not return to its normal shape and size. This can create a 'leaky' cell. Water is at its densest at about 39 degrees F, so when cold water is imbibed, it may result in additional membrane damage," Kruger says. "In the plant this action may somewhat disrupt the embryo/endosperm enzymatic conversion to energy, but mostly results in leakage of cell solutes and sugars. This, in turn, is likely to reduce growth rate and interfere with normal regulation and growth of the emerging seedling."

Now that temperatures have popped to more seasonable levels, some farmers might still be worried about the possibility of crop damage or lower yield potential because the seed's been sitting in cool, damp fields. If this describes you, you can get an idea of whether your seed's hurting by following a few simple scouting tips.

"To assess the impact of freezing temperatures on emerged corn, check plants about 5 days after the freezing injury occurred (and preferably when growing conditions conducive for regrowth have occurred). New leaf tissue should be emerging from the whorl," Thomison says. "You can also observe the condition of the growing point (usually located 1/2 in to 3/4 in below the soil surface) by splitting seedlings lengthwise. If the growing point appears white to light yellow and firm several days after the frost, prognosis for recovery is good."

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