COLUMBIA, Mo.– Most of 2013 has been much wetter and cooler than 2012, but heading into fall Missouri is experiencing heat and dryness that, coupled with earlier weather, could hurt corn and soybean yields.

Bill Wiebold, a University of Missouri Extension crop specialist, says it’s almost a tale of two states within Missouri.

“We have pretty wet conditions, or have had until recently, in the southern part of the state with floods and that kind of damage,” Wiebold says. “And then we’ve had really dry conditions when you go from Highway 36 to the Iowa border. It has really been very dry—dry enough that we’re going to have low yields because of that.”

Even though grain filling is nearing its end, the plants are still sensitive, says Wiebold, who is also a professor of agronomy in the MU College of Agriculture, Food and Natural Resources.

“As dry as it is, I think we’re going to have corn actually dying because of the dry conditions rather than normal maturity,” he says. “When plants die too soon, of course, they have smaller grain and lower test weights.”

The wet spring that delayed planting of corn and beans and the cooler conditions that prevailed much of the year are also concerns. Temperatures in July were about 2 degrees lower than normal and August temperatures averaged almost 3 degrees below normal.

Wiebold says that with the cool weather there have been fewer growing degree days than in a normal year. Growing degree days are an accumulation of heat units that determines the development rate for plants from emergence to maturity.

“It will delay maturity in corn,” Wiebold says. “Not so much in soybeans because in addition to temperature it is affected by the photoperiod, or length of day. So I think soybeans will mature relatively normally, although there is no doubt that late-planted soybeans almost always yield less than ones planted normally.”

While most crops were planted late, a broad range of maturities were planted this year, Wiebold says.

“Some corn was planted early before it started raining and that has moved through relatively quickly,” he says. “Other fields were delayed amazingly late this year, so we’ve got fields that are probably a month behind in terms of their maturity.”

Despite the lateness of the crop, there isn’t much concern about frost damage. But farmers should expect lower yields.

“I think there are lots of things that are weather-related that are combining to say that probably our yield this year is going to be less than normal,” Wiebold says. “This will be the fourth year in a row we’ve had below trend line yields in Missouri.”

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