Issue No. 9, Article 4/June 3, 2011
Too Late to Plant?
Warm and dry weather in parts of Illinois this past week has allowed some progress in getting crops planted. Corn planting in Illinois was 94% complete by May 29, and soybean planting was 59% complete. While not close to last year's numbers, these aren't too far off the 5-year averages, "helped along" by the late planting in two of those five years.
It's inevitable when corn and soybean acreages remain unplanted on June 1 to start hearing the question "When is it too late to plant?" Although prevented-planting insurance changes things, there's no "drop-dead" date for planting. Instead, we need to consider what yields can be expected as planting stretches into June. Using this information, we need to decide at what point yield levels and added costs of planting will make the crop less profitable than collecting insurance.
Based on previous studies, we expect that corn has lost about 25% of its maximum yield when planted the first few days of June. That number will seem high to some and low to others, based on experience. The number really is highly variable; we have had 200-bushel corn that was planted in early June, and we have had yields near zero. The only factor that's of some use when trying to guess where within this yield range a field might fall is soil productivity: planting onto soils with good drainage and high water-holding capacity will very likely mean higher yields than planting onto droughty or heavy, poorly drained soils. Of course, few of the former fields typically are last to be planted.
Hybrid should probably not be changed to an earlier-maturing one in central and southern Illinois (unless the first-choice hybrid in central Illinois was late--in the range of 114-day RM or higher). In northern Illinois, where we expect GDDs to total about 2,550 from June 1 to 50% chance of frost, hybrids of 110 RM or later maturity might be switched for an earlier number if planting is much later than June 1. It's not advisable to drop by more than 5 or so RM, and then only if planting is delayed past the first week of June in northern Illinois or the second week in central Illinois.
There shouldn't be many changes in other agronomic factors when planting is delayed into June. If nitrogen has not yet been applied, the rate should be reduced by 10% to 15%. This is not because of reduced yield potential, but rather because nitrogen applied so late--and so close to the time of rapid uptake--is usually available to the crop with little loss. This is especially true when anhydrous ammonia is sidedressed after emergence. Plant population needn't be changed much either, though on lighter soil planting rates shouldn't be higher than the low 30,000s, since corn planted late is more likely to experience water stress.
Is there a date at which you should simply abandon the idea of planting for this year? That of course depends on what insurance you have taken out. But between June 1 and June 15-20, you can expect to lose another 25% of potential yield, bringing yields down to about half their full potential. Variability of actual yields following such late planting actually decreases some, but only because low yields become more likely and good yields become rare indeed.
The "glide path" for soybean yields as planting is delayed into June is less steep than for corn, but the "half-yield" date for soybean may be only a week or so later than for corn, perhaps two weeks later in southern Illinois. But at current prices--with the corn price per bushel only about half the price of soybean--soybean has a smaller margin to work with. This means that the planting date at which returns are equal is later than when the price ratio is less favorable to corn.
With some very heavy rain coupled with high temperatures following soybean planting this past week, some substantial stand loss can be expected, especially where water stood for a day or two. There's little guesswork here--soybean seed will last barely a day submerged at 85 or 90 degrees, especially if the germination process has started. Stand loss for both soybean and corn will be common in low areas where water stood this past week, and replanting these areas should be considered if it can be done within the next week or two.--Emerson Nafziger