No. 8/May 15, 1998
Corn Planting and Early Growth
Heavy rains following late-April or early May corn planting have caused damage in some fields. Some of this damage is from standing water. Seeds or seedlings can probably survive a maximum of about 7 days under water, including the time after the water drains from the soil surface but the soils remain saturated. Mushy, discolored seeds and seedlings will clearly indicate that the only way to have plants in the wet spots is to replant.
I have also had a few reports of fields that will probably have to be replanted, even though areas of the field were not under water. In these cases, some plants are up, but digging for seeds that haven't emerged has revealed either soft, mushy seeds or, in some cases, shoots that emerged from the seed but then simply stopped growing. If the shoot on such seedlings is relatively short and spindly, then there is a good chance that the seedling died from lack of oxygen, probably as a result of saturated soils. If the shoot still appears to be growing, but is thickening rather than growing upward, then the problem is likely due to a physical barrier, most likely a crust. The crust formed quickly in some fields over the weekend as the surface dried. The problem is worse in fields that were worked wet and in places where seed placement was deeper than 2 inches or so.
Our data show that stands of early planted corn would need to be less than 80 percent of intended stands to justify replanting in mid-May. As time goes on, plants in the field become more "valuable," and the stand reduction needed to justify replanting becomes greater. Please refer to the Illinois Agronomy Handbook, page 23, for a fuller discussion ofreplanting in corn.
Counting plant stands will be popular over the next few weeks as the rest of the crop emerges. We suggest the "measuring wheel method" as a way to get more accurate counts. To use this method, push a measuring wheel while counting plants: We suggest counting by 3s up to 150 plants in one sample. Convert that to population by dividing the number from the following table by distance traveled (in feet) as you counted 150 plants:
Thus if you counted 150 plants in 100 feet of 30-inch rows, divide 2,613,600 by 100 to give a population of 26,136 plants per acre. We would suggest taking one such measurement for each 5 acres or so in "uniform" fields. Instead of stopping to calculate plant populations each time, the measuring wheel can be picked up and moved for additional counts. An average distance per count can then be calculated, and population calculated as described above.
Emerson Nafziger (email@example.com), Department of Crop Sciences,(217)333-4424