With only 10 percent of the Illinois corn crop planted by the end of April, growers are facing one of the slowest starts in recent years, said Emerson Nafziger, University of Illinois Extension agronomist.
Of this 10 percent, 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 said 3 percent of the state's crop, or 30 percent 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, he said. 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 said. “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 said. “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 said 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 said. “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 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, Nafziger said 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/ .
Meanwhile, in Indiana, while planting dates are important, Purdue Extension corn specialist Bob Nielsen says plenty of other factors can influence crop yield.
The prime time for planting corn to maximize yields in much of Indiana is April 20 through May 10. The window opens about a week later in northern Indiana and a week earlier in southern Indiana.
Because of the wet spring weather, very little corn has been planted. According to the USDA National Agricultural Statistics Service's Indiana Crop and Weather Report for April 24, only 2 percent of Indiana's corn crop had been planted, compared with the 15 percent five-year average.
"By itself, this is not much cause for concern, because typically only a very small percentage of acres are ever planted by this date in Indiana," he said. "However, the specter of delayed planting is clearly on the horizon because little other fieldwork has been completed. For some growers, tillage operations, herbicide applications and nitrogen fertilizer applications must be completed first before they can consider planting their crops."
According to the USDA NASS progress reports for the past 20 years, there is not a strong relationship between planting date and absolute yield on a statewide basis for Indiana.
"It is true that corn grain yield potential does decline with delayed planting after about May 1," Nielsen said. "But the planting date only accounts for 11-12 percent of the variability in statewide yields from year to year."
Yield potential declines with delayed planting because of factors such as shorter growing season, insect and disease pressure and moisture stress during pollination. The good news, Nielsen said, is that planting date is just one of many yield-influencing factors, or YIFs, for corn.
"What is important to understand is that yield loss to delayed planting is relative to the maximum yield potential in a given year," he said. "In other words, if all of the other YIFs work together to determine that the maximum possible yield this year is 200 bushels per acre, then the consequence of a 10-day planting delay beyond May 1 would be a yield potential of 190 bushels per acre.
But if all the other YIFs work together to determine that the maximum possible yield this year is only 160 bushels per acre, then the consequence of a 10-day planting delay beyond May 1 would be a yield potential of 150 bushels per acre.
Because of these other yield-influencing factors, it is possible for early-planted corn in one year to yield more than, less than or equal to later-planted corn in another year — depending on the exact combinations of factors for each year, Nielsen said.
The bottom line, Nielsen said, is not to succumb to the fear triggered by the prospects of delayed planting in 2011.
"'Mudding in' a crop early to avoid planting late will almost always end up being an unwise decision," he said. "Another reason that it is probably too early to fear-monger about the anticipated late start to planting is that growers have the machinery capacity to catch up quickly once the weather and soil conditions become favorable for planting."
For more on planting date and yield-reducing factors in corn, visit Nielsen's "Corn Planting Date is Important, But …" article online at http://www.kingcorn.org/news/timeless/PltDateCornYld.html .
Iowans roll in good weather
Corn planters are rolling in parts of Iowa. This is good news; the bad news is that only 3 percent of the crop was planted as of April 24.
On Monday, April 25, Iowa Secretary of Agriculture Bill Northey  commented on the current NASS Iowa Crops and Weather Report  and the slow corn planting progress to date. There was only a half-day suitable for fieldwork the previous week so little corn planting progress had been made.
As I write this on Friday, April 29, although planting has started again in some places, rain is forecast for tonight and tomorrow for parts of Iowa. Secretary Northey on Monday also presented useful historical crop planting information indicating that we can plant up to slightly more than 20 percent of our corn acres in one week, based on the five-year average. Remember though, the five year average includes one of the fastest planting seasons on record, 2010, and one of the slowest, 2008. Another way to look at this is to consider how many acres are planted per day suitable for fieldwork. On average, during any week this time of year, fields are suitable for work about 3.5 days, or half the time. We can put a lot of corn in the ground quickly!
Last year, based on data from the Iowa Crops and Weather Reports, Iowan’s planted from 37,000 acres per suitable day to nearly 1.4 million acres. In 2008 and 2009, over 1.2 million acres were planted per day suitable for field work during the best weeks.
Several factors contribute to our ability to plant rapidly. Modern planters are larger than older models, fields are larger, more fields have improved drainage with tiles, and global positioning systems, improved operating lights, planter monitors and well-equipped tractor cabs all allow farmers to plant longer hours with less fatigue. In addition, the common knowledge that yield penalties generally are less with early planting than late planting has spurred this trend. It remains to be seen how long it will take to plant our estimated 13.9 million acres this year. Iowa farmers are well-equipped to do it in record time, if the weather cooperates. We just need 10 excellent days!