Corn infected with the fungus Aspergillus flavus. The worst drought to hit the United States since the 1930s has farmers coping with a number of impacts, from cyanide poisoning in cattle to fungal infestations in corn. Image: Photo courtesy the International Institute of Tropical Agriculture
The drought that has kept much of the nation in its grip this summer brings a host of additional downstream worries for growers already struggling with reduced yields.
Cattle are being poisoned by cyanide-laced weeds in Arkansas. Across the Midwest water-soluble fertilizers are concentrating in soils and plants, making them harmful rather than productive. And in Missouri, samples suggest that more than half the corn crop isn't fit for human consumption, thanks to unusually high levels of a carcinogenic toxin.
For farmers coping with the worst drought to hit the United States in decades, it's another chapter in an unfolding disaster that shows no sign of abating. And with climate projections showing more frequent summer droughts in heavy farming areas, these elevated drought-related poisons add to the challenges growers face in a changing climate.
"I've been talking to veterinarians and other folks in Iowa since June, and I'd estimate somewhere around 150 cattle have died from toxic nitrate doses," said Steve Ensley, a toxicologist at Iowa State University College of Veterinary Medicine.
The annual tally is usually less than five, he said.
With nitrate, drought spurs high levels because plants take up nitrogen, applied as a fertilizer, but cannot convert it into useful compounds due to a lack of water.
"If the plant doesn't go through photosynthesis because it doesn't have the water to, the nitrate just stays in the plants," Ensley said.
Nitrate isn't toxic to animals. But microorganisms in the environment convert it to a compound that, at high levels, inhibits oxygen flow in animals, resulting in difficulty breathing, weight loss, lack of appetite, sometimes death.
For humans, nitrate brings two main health issues: blue baby syndrome and digestive tract cancers [pdf].
But the danger to humans is through drinking water. Nitrogen fertilizer not sucked up by plants often washes into streams and lakes. This summer's dryness has sent less nitrogen-laced runoff into Midwest streams, Ensley said.
But the leaching could just be delayed.
"It's probably still in the soil," Ensley said. "When it rains, there's definitely the potential for some heavy runoffs."
Extended drought can often induce a highly toxic and cancer-causing toxin – aflatoxin, a fungal-byproduct. With the corn harvest underway, aflatoxin worry is pervading the farming community.
"We don't know how bad it'll be yet," said Don Parrish, senior director of regulatory relations at the American Farm Bureau Federation. "But the conditions certainly exist."
Several fungi, or molds, can grow on drought-stressed grain, and several of these produce byproducts are toxic to animals and humans. The most common of these fungi, Aspergillus flavus, consumes the starch inside corn kernels and produces a byproduct named aflatoxin. This fungus also contaminates peanuts, cottonseed, pecans and grain sorghum. The disease causes olive green, moldy growth.
Drought doesn't cause the fungus, but the dryness allows for cracks in the shell protecting the kernels, allowing fungus to get to the grain.
"We've had an increase in aflatoxin all over the state," said Ron Heiniger, professor of crop science at North Carolina State University. "We had the prolonged heat stress, and then recent rainfall.... It's just blowing up."