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Erin Ehnle Brown / Grand Vale Creative LLC

Cool temperatures have put soybeans behind in development. Will they mature prior to frost?

FARGO, N.D. — A cool, comfortable late August was good for recreation, but may leave some of the region's soybeans for "growing degree days" that allow the crops to mature before a frost.

Hans Kandel, a North Dakota State University Extension agronomist, in the first week of September said farmers aren't likely to make up many growing degree days between now and harvest, considering the forecast of cooler temperatures in the next few weeks.

Soybeans are behind in development because they were planted late, and then falling behind in heat units, he said. "The good thing about soybean is that the soybean (yield) is made in August and September rainfall," he said.

Hans Kandel, North Dakota State University Extension agronomistThe weekly National Agricultural Statistics Service crop progress report on Sept. 1 pegged the North Dakota soybean crop at 9% poor, 27% fair, 57% good and 7% excellent. Only 7% of the soybeans were dropping leaves, an indicator of maturity. That's well behind the 35% last year and the 25% average for the date over the past five years..

In Minnesota, the NASS report said soybeans were two weeks behind, with only 7% turning color, which was 10 days behind last year and average.

"We are behind, but we should be finishing out the season in that Sept. 20 to Sept. 25 area, if you planted the correct maturity and planted at a reasonable time," Kandel said, adding, "If you planted into June, the maturity is expected in late September."

Typically, the frost date long-term is about Sept. 20 in central North Dakota, while in the past years the frost date has often delayed until October.

"With soybeans we try to harvest it directly, close to a storable moisture and you can still air-dry the soybeans," he said. "Beans need to be mature because immature beans are dockage. Physiological maturity for soybeans means that 95% of the soybean pods have a mature color.

"When you get an early frost, typically we get some of the beans that do not mature completely. You may get green beans into your bin," he said.

For the past two years, NDSU has offered farmers an online computer model for soybeans. The model takes 1) planting date, 2) variety maturity, 3) and data from the nearest North Dakota Agricultural Weather Network weather station. "It will predict the day it might mature," as well as the first frost-date long-term, and the first killing frost of 28 degrees Fahrenheit. The model works best if the crop is planted within May.

Similarly, a killing frost can stop the maturing of a corn kernel toward harvest, indicated by black layer in the kernel.

NASS pegged North Dakota corn at 74% in good to excellent condition, but only 72% was in the dough stage, well behind the 95% last year and behind the 87% average for the date. Only 8% was dented, behind last year's 67% and the 44% five-year average.

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