How early is too early for planting corn?

By Brad A. Miller, C.C.A., Territory Agronomist for DEKALB & Asgrow, Northern Ohio

With the unseasonably warm temperatures and good field conditions many producers have
considered, or may have already begun, planting corn. Curren highs have been reaching into the
80’s and the extended forecast looks favorable, making the thought more tempting. Current soil temperatures
are near 60° F and the favorable temperatures are allowing us to collect as many as 15 growing degree units (GDU) per day. These soil temperatures are high enough to begin germination. Corn requires about 120 GDUs to emerge after planting. If conditions stay similar, as indicated by the forecast, enough GDUs would be collected if corn were planted on March 23 to possibly emerge by March 31.

There is considerable risk when planting this early, however. The earliest dates with a 50% or less chance of frost (32°F) range from April 20 for areas immediately adjacent to Lake Erie to May 15 in east central Ohio. A 50% probability of frost (32°F) exists for Bucyrus after April 29, for Hoytville and Newark after May 2, for Warren after May 17, and for Wooster after May 3rd. This leaves a substantial amount of time that frost could have an impact on corn from these early planting dates.

The growing point of a corn plant remains under ground typically until the V5 to V6 growth stage. This helps protect it from damage by frost and may allow it to recover if a frost does occur. However, depending on the severity of a frost, corn can still be impacted. In a study conducted in Wisconsin, plants at the V2 stage of growth were either all cut off at the ground level to simulate a frost that killed the entire above ground portion of the plant, or only half of the plants were cut off to simulate a light frost. When all of the plants were cut off, yield was reduced by 8% and when only half of the plants were cut off yield was reduced, but not significantly. Typically, corn is more likely to recover during earlier stages of growth, but as it matures into later stages, V4 and beyond, there are fewer reserves left in the seed to support re-growth of the plant. The other risk is that if a freeze is severe enough, it could kill the growing point even while still beneath the soil surface.

If a grower were to decide to begin planting he might be tempted to plant shallow to encourage quicker emergence. This could be a mistake as it may also push the growing point of the plant closer to the surface more rapidly, allowing greater exposure to damage from cold temperatures. It may be wise to plant corn between 1.75 and 2 inches, if pursuing these untypically early planting dates.

There is substantial risk involved with planting corn in mid- to late-March and producers should weigh these risks carefully. Corn planted in mid– to late-April will typically out yield corn planted in March, with much less risk associated with that timing. Growers may be wise to leave their planters in the shed for a couple more weeks, waiting for when the risk from adverse temperatures is greatly reduced. This time may be best utilized for planter and sprayer maintenance and calibration.

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