Corn diseases lurk in bumper U.S. crop, threatening yields

This is a cornfield in Mill Hill, Pa., on Aug. 29, 2023. (AP Photo/Gene J. Puskar)

CHICAGO — High levels of fungal disease are lurking in corn fields across the U.S. Midwest, threatening to reduce yields of a record-large crop and cause headaches for farmers during the autumn harvest, growers and crop experts said.

The outbreaks are a blow to farmers in the world’s biggest corn-producing country as they struggle to make money due to low grain prices and rising costs for fertilizer, seed and other inputs. Farmers had hoped to produce the biggest possible yields to offset low prices, and crop diseases put that plan at risk.

“I’ve never seen disease as severe as I’ve seen this year,” Iowa State University plant pathologist Alison Robertson said.

The U.S. Department of Agriculture projected in August that farmers would produce a record-breaking yield of 188.8 bushels per acre. However, most analysts in a Reuters survey expect the government to lower its estimate in a monthly report on Friday, due partly to disease. Their estimate for a yield of 186.2 bushels per acre would still set a record and produce ample supplies.

The main culprit is southern rust, which blows northward from tropical regions and can reduce yields by up to 45 per cent, according to the Crop Protection Network, a consortium of university experts.

The disease often reaches the Midwest in August, too late to impact output much. This year, it arrived by mid-July in Iowa, the biggest corn-producing state, leaving plenty of time to wreak havoc. It was the state’s second-wettest July on record, which created favorable conditions for fungus to spread.

“We kind of had the perfect storm” for rust, Robertson said.

Participants on a tour of Midwestern farms came face to face with outbreaks last month. After trekking into fields, they emerged with rust-colored dust covering their sleeves.

DISEASES ATTACK CORN LEAVES

Another disease, tar spot, was also widely detected.

Both fungal diseases attack corn leaves and interfere with photosynthesis. In corn plants, the process converts sunlight and water into sugars needed to produce grain. Infected corn plants often produce smaller kernels, reducing yields.

Fungicides can mitigate the damage, and many farmers applied them this summer. But applications cost money at a time when some growers can hardly cover their production costs.

In southwest Iowa, farmer Roger Cerven said southern rust was so bad that he feared losses of 30 bushels an acre even on fields he sprayed.

“The fungicide was a Band-Aid, and we needed a tourniquet,” Cerven said.

The full extent of yield losses won’t be known until farmers bring crops in from the fields.

Some growers already started harvesting in areas where disease prompted plants to stop growing and turn brown prematurely, said Brent Judisch, a farmer in Cedar Falls, Iowa.

Harvesting may be difficult, as infected plants tend to cannibalize their stalks and roots for sugars needed to fill kernels. The resulting hollowed-out stalks are prone to falling over.

“Imagine driving through a pile of Pick-Up Sticks, trying to harvest all the corn,” Robertson said. “It’s just a nightmare.”

(Reporting by Julie Ingwersen. Editing by Tom Polansek and David Gregorio)