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Rain Delay 2002--Holding On

May 10, 2002
It takes an extra dose of patience to watch rain systems move through Illinois in early May and to hear forecasts for more of the same. What looked like a temporary setback with the rains in the last half of April has turned into something that looks considerably less temporary. If there's any comfort here, it's that no one is alone in this; that it's not some sort of "failure" that we should have foreseen and prevented; and that, despite what things look like, the rains will end and it will dry off so that planting can resume. How long that will take is a guess, but history tells us it will happen.

We can choose to be optimistic--as recently as last year, May rainfall was very heavy in northwestern Illinois, planting was delayed until the last half of May in many areas, and yet the regional corn yield was above the state average. Realistically, although yields of corn planted late can be very good, the odds of getting high yields decrease as planting is delayed. One way to think of this is that high yields from late-planted corn simply require weather conditions--primarily rainfall--for the rest of the season to be better than historical records show to be highly likely. We remember when we had late planting followed by good yields because that was an exception, not because it was expected.

It could be worse. The National Agricultural Statistical Service indicates that corn planting by May 5 was 42% complete nationally, compared to a 5-year average of 51% on that date. Indiana and Ohio were 10 and 11% complete, Illinois was 30%, and the western Corn Belt states were at or above 50%. In 2001, though, we had almost 90% of our corn planted in Illinois by this date. If there are any bright spots from all this, it is that the stands of corn that were planted in April are quite good, with the rain helping to prevent crusting. Warmer soil temperatures from now on will also mean rapid germination and emergence, providing we don't return to crust-forming conditions. Crusting is increased when soils are too wet at planting; when planting is followed by hard rainfall; and when the weather turns sunny, warm, and windy after planting but before emergence, essentially "baking" the soil surface into a crust.

As we wait for soils to dry out in much of Illinois, thoughts are turning to management changes that we might consider in an attempt to improve chances for better yields of late-planted corn. The most common questions have to do with changing to earlier-maturing hybrids. Producers in northern Illinois (where conditions this week have not been as wet and where planting progress is therefore better in many areas), who planned to use fuller-season hybrids (which we might define as longer than about 111 days CRM in that area) might want to switch to hybrids a little earlier than that if planting is delayed past May 20 or so. In central and southern Illinois, where most hybrids used are in the 110- to 115-day relative maturity range, there is little reason to switch to earlier hybrids if planting can be done in May. Earlier hybrids will have drier grain in the fall and so will require less drying cost; but they will also tend to yield less, which can quickly cancel out savings from drier grain. If you have fields that you feel won't be planted in the next two weeks and you were planning to use hybrids later than 113 days CRM, then you might consider switching now, but probably to something not earlier than 108 days or so. Very early hybrids were not developed for the southern half of Illinois and so have often not been tested thoroughly under these conditions.

The Illinois Agronomy Handbook ( has information relating planting date to chances of the crop reaching maturity before first frost. These maps are based on the growing degree-day (GDD) requirements for corn hybrids and on what weather records tell us the average GDD accumulations will be. Work in Indiana and Ohio has shown that hybrids planted late require less than their normal GDD to reach maturity. The average decrease in this requirement was found to be 6.8 GDD for each day of delay after May 1. That means that a hybrid that needs 2,700 GDD if planted on May 1 (which would be typical for a hybrid of about 111 days CRM) would need 136 fewer GDD, or only 2,564 GDD, if planted on May 20. While that means that we should be slow to change to earlier-season hybrids as planting is delayed, we should also understand that a decreased requirement for GDD almost always is related to a decreased yield. There is no "free lunch" here.

Are there any other management changes we should consider as planting is delayed? While we have not seen strong evidence that corn planted later has a lower optimum plant population, percentage emergence tends to be slightly better with late planting; and if we are planting in fields where drought is more likely, we might want to back off plant population slightly, especially if normal practice is to push populations above 30,000. In a general sense, corn planted in the second half of May more closely matches the crop's subtropical habitat and so will respond favorably to warm soils and warm temperatures. There are no obvious extra requirements for the crop when it's planted late. Let's just hope the weather breaks and we're backing in planting before the end of the month.--Emerson Nafziger

Author: Emerson Nafziger

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