The question on everyone's mind these days is with late planting and cooler-than-normal temperatures, will corn and soybean crops get finished on time before fall frost strikes.
Cooler-than-normal temperatures have set back crop development, including pod formation and filling in soybeans, and grain fill in corn remains well behind normal, says University of Illinois crop sciences professor Emerson Nafziger.
“Corn is 10 days to two weeks behind normal, and soybeans are two to three weeks behind normal. The number of days behind will ‘stretch’ as the weather cools, so late crops get even later,” he says. “Ten days behind in mid-August will become 15 or 20 days behind in mid-September even if temperatures are normal.”
Late-planted corn often requires fewer growing degree days (GDDs) to reach maturity than early-planted corn. Nafziger says that this lowered GDD requirement is often reflected in lower yield as the crop experiences stress during high temperatures and dry weather in mid-summer. This year, however, with temperatures generally below normal in recent weeks, accelerated development is not expected, he says.
“Instead, we are seeing that corn development is following closely the normal number of GDDs required to reach each stage. This means less chance of premature death and a better chance to fill grain completely. But for late-planted corn it also means late maturity,” he adds.
Nafziger says if normal GDD accumulations in August and September occur, corn planted in central Illinois, for example, on May 1, May 15, and May 31 will accumulate about 3,020, 2,850, and 2,530 GDD, respectively, by the end of September. If a mid-season (111-day relative maturity) hybrid needs 2,700 GDD from planting to maturity regardless of planting date, corn planted on these dates should reach maturity (black layer, about 32% grain moisture) on about Sept. 5 to 10, Sept. 15 to 20, and mid-October, respectively.
“The crop seems to be on course to do this. Corn planted in early May is at stage R3 (milk stage) now, while corn planted in late May or early June is just finishing pollination. This reflects ongoing cool temperatures so far in August, and if these continue, maturity dates will be even later,” he says.
Read about the chances for frost and the prospects for the soybean crop as well as view the entire article at the ACES News  site.