Corn needs heat, rain: Recent combination of cool, dry conditions is unusual

Upper Midwest corn farmers will be watching both the thermometer and the rain gauge in the next few weeks. Their crop needs plenty of heat and moisture, and the region is coming up short on both.

Upper Midwest corn farmers will be watching both the thermometer and the rain gauge in the next few weeks. Their crop needs plenty of heat and moisture, and the region is coming up short on both.

"We could use more heat. And some areas are getting dry," says Kim Swenson, a Lakota, N.D., farmer and president of the North Dakota Corn Growers Association.

Sixty percent of North Dakota corn rated good or excellent in mid-August, according to the National Agricultural Statistics Service, an arm of the U.S. Department of Agriculture.

A wet spring that delayed planting and recent low temperatures, however, have hampered development of the corn crop. Only 10 percent of North Dakota corn had reached the dough stage by the middle of August, compared with the five-year average of 27 percent.

North Dakota enjoyed a record corn crop in 2012, in large part because abundant subsoil moisture carried the crop through a dry, hot summer. Subsoil moisture is in much shorter supply this year, increasing the need for rain -- and many North Dakota corn fields aren't getting it, Swenson says.


Unusual combination

In South Dakota, there's also concern over cool weather that slowed the development of corn. There's growing concern about moisture, too.

"The crops could use a drink," says Laura Edwards, South Dakota State University Extension climate field specialist.

Recent cool, dry weather across much of the Upper Midwest is unusual, she says.

Typically, cool weather is accompanied by cloudy skies, which increase the odds of rain, she says.

Likewise, hot weather normally is accompanied by clear skies, which decrease the possibility of rain, she says.

Edwards has studied historical data measuring growing degree days, or GDDs, in several South Dakota cities. GDDs are a commonly used measurement of heat accumulation that helps predict plant growth rates.

Since 1893, for instance, Brookings, S.D., annually has received 745 to 1,015 GDDs from Aug. 5 to the fall freeze. The exact number depends on whether it's a cold, average or warm year and when the first freeze occurs.


Some South Dakota corn fields may still need 750 to 1,000 GDDs to reach maturity. Based on the historical data, these fields may end up "cutting it close," Edwards says.

Recent cool weather doesn't mean greater odds of cool weather and an early frost in the weeks ahead, she says.

Through the middle of the August, 70 percent of South Dakota corn still rated good or excellent, according to the NASS.

Nervousness in Minn.

Minnesota's corn crop overall is faring all right, too, with 61 percent rating good or excellent in the middle of August, according to the National Ag Statistics Service.

The crop isn't as advanced as usual, however. Only 7 percent of Minnesota corn had reached the dough stage, nine days behind the five-year average.

Cool weather is a concern across the state, but particularly in northwest Minnesota where corn acreage has risen sharply the past few years. Daily mid-August temperatures in some northwest Minnesota communities averaged only in the low 60s and high 50s.

Because cool weather has slowed plant growth, Marshall County in northwest Minnesota needs to avoid a heavy frost until the end of September for corn to mature fully, says Howard Person, county agent.


"The corn still looks good. But it's late," he says.

Some farmers who planted corn "are nervous. They wish now they had planted less of it," he says.

Marshall County is OK on soil moisture, but more rain would help, Person says.

That's the case in Minnesota overall, too.

Sixty-five percent of the state still had adequate or surplus topsoil moisture in the middle of August. Most of Minnesota received below-average precipitation in late July and early August, however, and more moisture would be welcome, according to NASS.

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