Even with last week’s warm, dry Midwest weather, the march to maturity remained slow for the U.S. corn and soybean crops, but there continues to be no clear threat of frost for the late crops.

USDA on Monday in its weekly crop update reported that 21% of U.S. corn had reached maturity as of Sunday, up 9 points from a week earlier, but behind last year’s pace of 30% and well under half of the five-year average of 55%.

In the top corn state of Iowa, 22% of the crop was reported mature against an average of 55%, while in No. 2 Illinois, the crop continued to lag even farther behind at only 13% mature against an average pace of 69%.

The maturation of the soybean crop is speeding up as days grow shorter and photosensitive plants shut down. USDA pegged the portion of the U.S. soybean crop that was dropping leaves as of Sunday at 40%, up from 17% a week earlier, but still 18 percentage points behind the five-year average.

Some 50% of the Iowa soybean crop was reported dropping leaves against an average of 64%, but only 20% of the Illinois crop was shedding leaves against an average pace of 66%.

Crop conditions slipped a bit this week, but that is not unexpected with fields now finally reaching maturity.

USDA pegged U.S. corn conditions at 68% good/excellent, down from 69% last week, but 9 percentage points above a year earlier. Soybean conditions were rated 67% good/excellent, down from 68% last week.

The Iowa corn crop rating held steady at 75% good/excellent, while the rating for Illinois slipped 2 percentage points to 62% good/excellent. The Iowa soybean crop rating slipped 2 points to 73%, while the Illinois soybean rating fell 1 point to 60% good/excellent.

The soybean crop in northern-producing states is rapidly moving past the stage where frost can do yield damage with 85% of Minnesota’s crop said to be turning color along with 66% of North Dakota’s crop and 72% of Wisconsin’s crop.

The Illinois crop remains farthest behind, with only 54% of the state’s soybeans turning color against a five-year average of 82%, but there appears to be no risk of the crop there seeing a frost before October.

Weather forecasters said on Monday that the Midwest corn and soybean belt should remain free of frost through the end of September, with temperatures remaining above normal this week across most of the region.

Monday forecasts called for another mild week for the Midwest, with highs in the 70s and low 80s F and lows in the upper 40s and 50s.

"It continues to be a very favorable forecast, with no damaging cold weather in sight. That takes us through the end of the month," Mike Palmerino of DTN Meteorlogix told Reuters News Service, adding that the forecast virtually ends the threat of an early frost.

"Now the worst-case scenario is that you get a normal freeze. For most of the Midwest, the normal freeze dates are the first week to 10 days of October," he pointed out. Normal frost dates are in late September for most locations in the Dakotas.

Generally a freeze is considered normal if it falls within a week before or a week after the median freeze date.

The Midwest is expected to cool off late this week, with the National Weather Service’s six- to 10-day outlook calling for below-normal temperatures across the central and eastern portions of the Midwest Sept. 26-30. But temperatures are expected to remain comfortably above the freezing mark.

Monday’s computer weather models did show colder air to moving into the Midwest by Oct. 2-3, bringing potential for frost across the Dakotas, Minnesota, much of Wisconsin, lower Michigan and the northern third of Iowa, but forecasters are split over whether the air will be cold enough to cause a widespread frost.

Editor’s note: Richard Brock, Corn & Soybean Digest's marketing editor, is president of Brock Associates, a farm market advisory firm, and publisher of The Brock Report.