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Late-Planted Corn Gets a Boost From Nature

Late-Planted Corn Gets a Boost From Nature
Same hybrid planted later needs fewer heat units to reach maturity.

Plant a hybrid May 2 and seed from the same bag June 5, as happened in some cases this year, and the two at some point may not look like the same hybrid this season in some respects. Late planting has affects from the environment on the plant.

One of those is to reduce the number of growing degree days the plant needs to produce mature ears. Mature is defined as black layer, which often occurs around 35% moisture, give or take.

Small corn still has time: A natural tendency of corn planted late requiring fewer growing degree days to mature means this corn will likely beat frost.

Bob Nielsen at Purdue University and his counterpart, Peter Thomison at Ohio State University, determined a few years ago in tests that the difference can be up to 200 growing degree units. That can be significant if it is a cool summer, and/or there is the threat of early frost later in the season.

Growing Degree Day Units are calculated daily based on a minimum temperature of 50 degrees and a maximum of 86 degrees. Any temperatures in between contribute to plant growth.

The pair of specialists determined that number of GDDs needed to reach maturity actually begin to decrease around May 1. According to the Purdue University Corn & Soybean Field Guide, part of the decreased GGD requirement is the time it takes to reach silking from emergence.

Corn Illustrated Weekly

The largest gain, however, occurs from that point on into the season. They determined that based on their studies with hybrids of the time, for each day of delay after May 1, the GDD or heat requirement to reach relative maturity decreased about 6.8 GDD units per day.

Here's what that means. If a hybrid is full-season and needs 2,800 units in a normal year, planted May 1, it only needs 2,600 GDD units to reach black layer if planted May 31.

So if you live in Tipton County and planted a hybrid that normally needs 2,800 GDD units planted at a normal time on May 31, it now only needs about 2,600 units. Using historical data on the average first fall freeze date for Tipton, there should be an average of 2,700 GDDs between May 31 and that freeze date, which is October 23. So you can still expect the hybrid to mature.

The only catch, of course, is that the rest of the summer may not be normal. If it is cooler than normal then the hybrid may still race the clock.

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