With 89 percent of the Illinois corn crop planted by May 7, University of Illinois crop sciences professor Emerson Nafziger says the 2012 crop is off to a good start.
In most fields, emerged stands are very good, and the warmer temperatures now are starting to bring leaf color back as growth accelerates. Exceptions to the favorable crop conditions are in areas that received heavy rainfall or hail over the past week.
Some fields planted in mid-March that suffered frost damage have been replanted. "The March 16 planting here at Urbana, which we would have replanted if it had not been a trial, has recovered reasonably well, with the exception of those plants that either died or have grown back very slowly," said Nafziger.
"Still," he said, "the stand in these plots is very uneven down the row and at this point, the late March planting that escaped frost damage appears to have better potential than the mid-March planting."
Growing degree day accumulations in April were at or below normal, with only 258 GDD in Urbana. That follows 211 GDD in only the second half of March. About 170 GDD accumulated in the first 10 days of May.
"This means that the corn planted on March 16 at Urbana has accumulated about 650 GDD by now, and corn planted on April 1 or April 20 has accumulated about 440 and 260 GDD, respectively, through May 9," said Nafziger.
While the 650 GDD accumulated from March 16 to May 9 would normally be enough to bring corn to the V7 stage, corn planted on March 16 and then frosted is showing a range of development stages, with the most advanced plants at V6 (six leaves fully emerged) and 10 to12 inches tall. Plants with more injury from frost are at V5 and are quite short for that stage. Corn planted on March 29 is at or near V5 and 6 to 8 inches tall, while corn planted on April 19 is nearing V2.
Average GDD accumulations over the past 10 years at Urbana are: 432 in May, 667 in June, 761 in July, and 729 in August. For an early-planted crop that has accumulated 650 GDD by May 9 and requires 1,350 GDD to pollination and 2,750 GDD to physiological maturity, pollination will most likely take place during the third week of June. The crop should reach maturity during the third week of August.
Early April planting will need about 200 GDD, or about 10 days more, than a mid-March planting to reach each stage, so it should pollinate in late June and mature in late August. Corn planted in mid-April will need only about 100 GDD, or 5 days more, than corn planted in early April; it should pollinate the first week of July and mature the first week of August. Corn planted in late April will need an additional 5 days.
Most of the state has received some rainfall over the past two weeks, allaying concerns about dry weather settling in. Over the next month, as the crop builds the leaf area, stalks, and roots, it needs to set kernels and fill grain, it will also be increasing its capacity to withstand periods of dry weather. If both rainfall and temperature remain about average for the 2012 growing season, prospects for the crop are good.