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Published July 13, 2015, 09:49 AM

Haze shouldn't cause significant crop damage

Growing crops need sunlight and heat — and smoke from Canadian wildfires meant less of both for Upper Midwest fields in late June and early July.

By: Jonathan Knutson, Agweek

Growing crops need sunlight and heat — and smoke from Canadian wildfires meant less of both for Upper Midwest fields in late June and early July. Though the persistent haze and overcast skies aren’t expected to do significant damage to crops, some, particularly corn, could be affected, farmers and agronomists say.

“The haze has reduced temperatures,” says Joel Ransom, North Dakota State University Extension Service agronomist. “We haven’t had the bright, sunny days. That’s more problematic for corn than for the small grains. My guess is, it won’t have any affect on the small grains. But there could be the potential for slight reduction in corn (yields).”

Though small grains such as wheat and barley generally fare best without high temperatures, corn thrives on heat. And even before the stretch of smoke-filled skies and reduced temperatures, corn in parts of the region received less heat and was less advanced than usual. For instance, none of Minnesota’s corn crop had silked by July 6, down from the five-year average of 6 percent for that date, according to the National Agricultural Statistics Service, an arm of the U.S. Department of Agriculture.

Crop disease impacts

The sky in parts of Minnesota, as well as North Dakota, South Dakota and Montana, was filled with the combined smoke of more than 200 wildfires in Alberta and Saskatchewan that strong winds pushed south.

Farmers and agronomists in the four states are still evaluating whether the cooler temperatures will boost or limit disease in their crops. Cool weather hampers some crop diseases, but is conducive to others, including white mold in canola.

“It stands to reason that these cooler temperatures could increase white mold pressure in canola,” says Ryan Pederson, a Rollette, N.D., farmer and secretary-treasurer of the Northern Canola Growers Association. “So that (potential disease impact) has definitely been on my mind.”

It’s unclear how much longer the Canadian wildfires, which military personnel are now helping to battle, will continue. But most of Western Canada currently has an above-average chance of wildfires for the remainder of July, according to the Canadian Wildland Information System website.

Wind directions and rain, which can wash pollutants from the air, also will affect how much smoke is in the sky and how long it stays there, weather experts say.

Natural disasters that block sunlight have a long history of hurting crops. An extreme case came in 1816, the so-called “Year without a Summer.” The 1815 explosion of Mount Tambora, on a remote island in the Indian Ocean, threw huge amounts of volcanic ash into the atmosphere. That led to prolonged stretches of overcast skies worldwide, cooler temperatures and reducing sunlight. Conditions were so severe that some farmers lost their crops, with food shortages reported in the U.S. and Europe.