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Heat helps late-planted corn

GRAND FORKS -- Corn should be knee-high by the Fourth of July, the old saying goes. The updated version of the adage is that to get a good harvest, corn should be waist-high by the Fourth.

Most of the Upper Midwest corn crop wasn't waist-high this Fourth, the result of a wet spring and late planting. But a burst of warm weather in late June and early July accelerated growth and raised optimism.

"There's been a lot of improvement recently," with some South Dakota corn reaching the waist-high mark by the Fourth, says Nathan Mueller, South Dakota State University Extension corn specialist.

Seventy percent of South Dakota corn rated good or excellent in the National Agricultural Statistics Service weekly survey in late June, he notes.

Only 66 percent of South Dakota corn rated good or excellent in late June 2012, when drought was worsening across the state.

There's another rule of thumb about corn: the crop thrives on heat and moisture. Late-June temperatures soared into the mid- and high 80s in much of the region, and the heat, coupled with ample topsoil moisture after widespread May and June rains, allowed many corn plants to grow rapidly, Mueller and others say.

"The corn looks a lot better than it did a week ago," says Kim Swenson, a Lakota, N.D., farmer and president of the North Dakota Corn Growers Association.

He notes that the region's 2012 corn crop was planted unusually early, allowing it to be more advanced than usual by the Fourth.

"It's unfortunate we went from one extreme to the other in the following year," Swenson said.

But even with late planting this year, 74 percent of North Dakota rated good or excellent in late June this year. Eighty-one percent of corn in the state rated good or excellent in late June 2012, according to NASS.

In contrast, only 58 percent of Minnesota corn rated good or excellent in late June this year, down from 82 percent a year earlier, NASS said.

Corn fields in much of southeast Minnesota were hampered by heavy spring rains that delayed planting, says Jeff Coulter, University of Minnesota Extension corn specialist.

Corn in northwest Minnesota and west-central Minnesota avoided the worst of the spring rains and generally looks better, he said.

Until recently, corn for grain was rare in northwest Minnesota. But faster-maturing varieties have encouraged many farmers there to begin growing, he said.

"We'd sure like to see them (northwest Minnesota farmers getting started in corn) have a positive experience that would encourage them to keep growing it," Coulter said.

Cooperative weather

Statewide in late June, Minnesota corn averaged 17 inches in height, roughly half the five-year average of 32 inches, according to NASS.

"I'm not terribly concerned about that," Coulter said.

Favorable temperatures and timely rains would allow Minnesota corn to continue to grow rapidly and provide an opportunity for good yields, he says.

Highs in the mid- and high 80s and lows in the 70s are best for corn, experts say.

If temperatures rise too high -- some experts say 92 degrees is the cut-off point, others say 90 degrees -- corn plants are hurt.

On balance, Upper Midwest farmers harvested a good corn crop in 2012, despite widespread drought. Plentiful subsoil moisture, combined with early planting, allowed many corn fields to overcome the lack of summer precipitation.

The region generally has far less subsoil moisture than it did a year ago, so the 2013 corn crop will require timely rains during the growing season, Coulter and others say.