There are reports of corn seedling growth problems in some parts of Iowa already this year, related to chilling damage and some due to variable emergence.
Sixty-four percent of Iowa's 2012 corn crop was already planted as of May 6. This is 6% ahead of the normal planting pace (see USDA report). The northeast and south-central cropping districts in Iowa were 50% planted by May 6 while the northwest and west-central cropping districts were around 75% planted. Indeed many farmers completed planting corn by May 6. The survey showed 7% of the state's soybeans were planted by May 6, which is slightly behind the 11% that is considered normal for that date, based on a five-year average.
"So far Iowa has experienced multiple corn planting 'windows' this year," points out Roger Elmore, Iowa State University Extension corn agronomist. "Farmers were rapidly planting the remaining corn crop this past week."
Walk your cornfields now to assess stands – and discover problems
In a May 1 ICM New article Elmore discussed how to think about corn that is yet unplanted, in terms of yield potential. Planting between May 15 and May 25, on average, results in 87% yield potential, according to ISU studies. "But remember," adds Elmore, "we have had some years where the best planting dates in terms of the yield we ended up with turned out to be the last planting dates of the season."
Also in that article he presents information and links on how to assess planted corn that may be a candidate for replanting. Refer to those guidelines if you are trying to make corn replanting decisions in mid-to-late May.
What are some of the 2012 corn conditions and field reports coming to Elmore from farmers, crop consultants and ISU Extension area crop specialists across the state this week? Elmore provides the following information and observations.
* Reports from emerging fields in 2012. Soil temperatures in late April backed off to 'normal' after an unusually warm March. "We all know that cooler soil temperatures slow the germination process and predispose seedlings to fungal infection and other problems – corn is a warm season crop," notes Elmore. "My colleagues and I have observed and heard reports of corn seedling growth problems in some parts of Iowa already this year. These problems are related to imbibitional chilling damage. This is shown in the photos accompanying this article. There are also some problems related to variable emergence of the corn this spring."
What is this so-called "imbibitional chilling" of corn seedlings?
Elmore says Imbibitional chilling refers to the chilling effect seeds may experience when they imbibe, or absorb water especially when soil temperatures are less than 55 degrees F for an extended period of time. Brittle shoot cell membranes rupture in cold soils. Seedlings may "corkscrew" and may not emerge when exposed to these cool soil temperatures. This may also happen when there are rapid swings in air temperatures. "Fortunately, most fields we've seen or heard about are exhibiting less than 5% of the plants affected," says Elmore. "If these plants do emerge, they will not likely be productive."
In addition, it is not hard to find fields this year with variable plant emergence in both reduced and minimum tillage, as well as maximum tillage, as another one of the photos accompanying this article shows. "Variable emergence and growth reduces yield if the corn development stages vary by two leaves or more," he says.
What agronomists like to see happening in cornfields at this time of year
"We like to see uniform emergence and growth," says Elmore. Perfect plant spacing within a row – a picket-fence stand – is less important than uniformity of emergence and attaining optimum plant populations, he explains. You need to adjust planters, planter speed and seed depth properly. And of course, plant into good seedbed conditions--'mudding in' corn results in mediocre results. "Do what you can to end up with the right number of plants per acre, that all look and develop the same," advises Elmore. "2012 promises many opportunities to learn more about growing corn."