A Disease Cuts Corn Yields

It has come on like a tidal wave, washing across the Corn Belt from Minnesota to the Texas panhandle, a disease that few farmers had seen until five years ago.

Known as Goss’s wilt, it has cut some farmers’ corn yields in half, and it is still spreading. This summer it reached Louisiana, farther south than it had ever been identified. Alison Robertson, a plant pathologist at Iowa State University, estimated that about 10 percent of this year’s corn crop would fall to Goss’s.

The disease, named for R. W. Goss, a longtime Nebraska plant pathologist, is caused by a bacterium with the formidable name Clavibacter michiganensis subsp. nebraskensis. When a plant is damaged by hail or other heavy weather, the microbe enters the wound and infects its vascular system, scarring the leaves with brownish-yellow lesions sprinkled with black freckles.

The infection may or may not kill the plant, depending on when it comes, but it almost always curtails yields. And for farmers who have never seen the infection before, it is deeply disconcerting.

“The farmer who called me had found a circle of corn about 50 feet in diameter or so that had strange symptoms, stalks broken over and twisting, discoloration, the whole nine yards,” said Clayton Hollier, a plant pathologist at Louisiana State University. “I hadn’t heard symptoms like that since I learned about Goss’s in college.”

Until 2008, Goss’s wilt had been confined to western Nebraska and a handful of counties in eastern Colorado. But that year it was found in Iowa, Illinois, Indiana and Wisconsin.

In 2011, a particularly virulent year, farms in much of Illinois lost as many as 60 bushels of corn per acre to the disease (the usual yield is 200 bushels per acre). So did many counties in Indiana.

While there are no official tallies, the last two years do not appear to have been as bad — thanks in part to dry, hot weather, which tends to keep the disease at bay. But its continuing spread is worrying farmers and plant pathologists throughout the Corn Belt.

No one is certain why Goss’s wilt has become so rampant in recent years. But many plant pathologists suspect that the biggest factor is the hybrids chosen for genetic modification by major seed companies like Monsanto, DuPont and Syngenta.

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