Illinois corn off to good start
With 89 percent of Illinois corn planted by May 7, the 2012 crop is off to a good start. In most fields, emerged stands are very good, and the warmer temperatures are starting to bring leaf color back as growth accelerates. Exceptions to the generally favorable conditions are in areas that received heavy rainfall, along with some hail, over the past week. Across Illinois south of I-80, rainfall totaled 3 to 4 inches over the past 10 days. Fields with severe hail damage, such as plants crushed into the ground, and low places where water stood for several days may be candidates for replanting.
Some fields planted in mid-March that suffered frost damage have been replanted. The March 16 planting here at Urbana, which we would have been replanted if it weren't a research trial, has recovered reasonably well, with the exception of plants that either died or have grown back very slowly. Still, 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 the month producing only 258 GDD at Urbana. That follows 211 GDD in only the second half of March. About 170 GDD accumulated in the first 10 days of May, so through May 9 the corn planted on March 16 at Urbana has accumulated about 650 GDD, and corn planted on April 1 and April 20 has accumulated about 440 and 260 GDD, respectively, through May 9.
While the 650 GDD accumulated from March 16 to May 9 would normally be enough to bring corn to the V7 stage, frost damage has resulted in a range of development stages for the corn planted on March 16 at Urbana. The most advanced plants are at V6 and stand 10 to 12 inches tall, while plants that had 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 May, 432; June, 667; July, 761; and August, 729. 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, we can project that pollination will take place the third week of June and that the crop should reach maturity the third week of August. An early-April planting will need about 200 GDD more, or about 10 days, to reach each stage, so it should pollinate in late June and mature by about the end of 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.
Most of the state has received some rainfall over the past two weeks, and this has allayed 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.
Emerson Nafziger is an agronomist with University of Illinois Extension.