Corn Disease Alert

ROCKVILLE, Md. (DTN) -- A little-known, new corn disease has suddenly surfaced in nine U.S. states this summer.

Researchers are scrambling to learn more about the disease, known for now as bacterial leaf streak, which originated in South Africa.

"There is currently limited information about this disease and what impacts it may have on corn production," said a Colorado State University release compiled by seven university plant pathologists. "There is also little known about the epidemiology of the pathogen."

Bacterial leaf streak has surfaced in field corn, seed corn, popcorn and sweet corn, and so far, it has been confirmed in Colorado, Iowa, Illinois, Kansas, Minnesota, Nebraska, Oklahoma, South Dakota and Texas.

The disease may have been here for a couple years, University of Nebraska plant pathologist Tamra Jackson-Ziems wrote in a UNL article on the disease. "Over the last two years, the clinic has received disease samples from numerous counties across much of Nebraska, indicating the disease may be widespread and producers and others should be monitoring for its development," she wrote. "Confirmation of the disease identification was delayed because of the lack of historic research on the pathogen and limited data on this bacterium and its close relatives."

On August 26, the USDA Animal and Plant Health Inspection Service (APHIS) released a statement on the disease confirmations and noted that "this plant disease presents no health risks to people or animals, and there is no evidence of adverse impact on corn yield or quality from this plant disease."

SYMPTOMS

Along with its mysterious entrance into the Corn Belt, bacterial leaf streak will likely be difficult for growers to identify, Jackson-Ziems noted.

The disease produces lesions that look very similar to common fungal corn diseases, particularly gray leaf spot. The lesions appear within leaf veins and are long and narrow, with wavy borders. They can be tan, brown, or orange and they tend to start on lower leaves of the plant, as early as V7 growth stage, before moving upward in the canopy, according to the Colorado State article.

"Gray leaf spot lesions may more commonly have straight, smooth margins, in contrast to those of this bacterial disease that often have wavy leaf margins," Jackson-Ziems wrote. "It is possible to have this and other diseases, like gray leaf spot, on the same sample, further complicating diagnosis."

Jackson-Ziems and others are urging growers to send any suspected cases of bacterial leaf streak to a plant diagnostic lab for confirmation.

LOOKING AHEAD

With no data on the disease's development or transmission, scientists don't have many management recommendations to offer farmers, the Colorado State article noted.

It most likely survives on infected corn stubble, and is transmitted by wind or rain onto corn plants. Plant pathologists do know it does not require a plant wound to infect and instead sneaks in via small holes in the plant leaves called stomata. The disease appears to thrive in irrigated fields in hot conditions.

"Like other bacterial diseases such as Goss's blight, no effective chemical controls currently exist," plant pathologists wrote in the Colorado State article. "Until more research has been conducted to determine the most effective management strategies for this disease, corn producers are advised to use standard management practices for bacterial disease."

That means using crop rotation or tillage to reduce the risk of bacteria surviving between seasons, the scientists said. "While both of these strategies may reduce the amount of the pathogen present, neither will eradicate the bacteria and eliminate the risk of disease," they concluded.

For more information, see the Colorado State article here: http://bit.ly/…, Jackson-Ziems' article here: http://bit.ly/…, and articles on the disease from Iowa State: http://bit.ly/… and the University of Illinois: http://bulletin.ipm.illinois.edu.

You can find the APHIS release on the disease here: http://bit.ly/….

Emily Unglesbee can be reached at Emily.unglesbee@dtn.com

Follow Emily Unglesbee on Twitter @Emily_Unglesbee

(PS/CZ)

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