With only 10% of the Illinois corn crop planted by the end of April, growers are facing one of the slowest starts in recent years, says Emerson Nafziger, University of Illinois Extension agronomist.
Of this 10%, about half was planted the first week of April and half the second week of April. Planting came to a halt in mid-April, and many fields remain wet today.
Nafziger says 3% of the state's crop, or 30% of the planted crop had emerged by May 1. This has raised concerns about the long delay between planting and emergence for most of the crop and the possible effects of the cool, wet weather on the yield potential of the crop that did emerge.
April was both wet and cool, accumulating 231 growing degree days (GDD) at Urbana, and more than half of those occurred in the first 13 days of the month. It takes about 115 GDD for corn to emerge after planting. This means that only corn planted before April 14 received enough GDD to emerge by the end of April.
"If fields planted before April 15 have not emerged by May 5 or so, we need to find out why and do so soon," Nafziger explains. "Some reports say corn seedlings are showing the twisted growth and root proliferation that we associate with 'chilling injury,' which is physiological damage from seeds taking up water with temperatures in the 30s or low 40s. Such seedlings often fail to emerge and may require replanting."
Other growers have noticed unevenness of emergence, with some plants emerging while others remain up to an inch below the surface.
"This could be coming from differences in drainage, or from seedling diseases or some insect injury," he says. "But if plants are uninjured and the differences are random down the row, it might be due to small differences in temperature and in planting depth. Such differences are magnified by cool soil temperatures, which tend to lag air temperatures in springs like this one."
So what about the crop that was planted the first week of April and is now up but growing very slowly? Nafziger says most of the crop that's up is in the 1- or 2-leaf stage, about where GDD accumulations say it should be.
"The lack of sunshine has the plants looking pale, and leaves are rather narrow as a result of slow growth," he adds. "But the stand is good, and there are no obvious deformities."
Although it is not possible to say with any confidence if the early-planted crop has suffered physiological damage that will limit its yield potential, Nafziger has seen cases where the weather turned cool after the crop had made more growth than it has this year with little effect on yield.
"This year, there has been little warm weather since these plants emerged," he said. "So we are optimistic that temperatures in the 70s will do much to return these plants to normal, with little lingering effect on yield potential."
The low April temperatures also mean that the growth advantage of early-planted corn will be less than normal, meaning corn planted the first half of May will not be as far behind corn planted the first half of April. For perspective, average GDD accumulations for the earliest-planted corn will be about 250 GDD more than corn planted now. Although 250 GDD is more than corn has accumulated during the past month, it is only about two weeks' worth by late May, and 10 days' worth by mid-summer.
For more information, read The Bulletin at http://bulletin.ipm.illinois.edu.