September 17, 2015


Corn disease discovered in Indiana, US



A corn disease, known as tar spot, had been identified by Purdue Extension plant pathologists in samples collected from a field in north central Indiana, US.


Diagnosed at the Purdue Plant and Pest Diagnostic Laboratory, the disease was also confirmed by a USDA national fungal identifier in Beltsville, Maryland.


The disease was previously not reported in the US, according to a Purdue University article. However, it is of no significant threat to yield in other areas where it is endemic including Mexico and Central America. Therefore, no action is required to deal with the diseases this late in the growing season.


Nevertheless, the potential impact of tar spot on corn crops’ yield in Indiana is still under observation, said Kiersten Wise and Gail Ruhl in an article published in the latest issue of Purdue’s Pest and Crop online newsletter.


“It is important to alert Extension specialists if you observe the disease to accurately document its distribution in the state,” they added.


Early symptoms of tar spot include brownish lesions on leaves. This was followed by the appearance of ascomata, black spore-producing structures that protrude from leaf surfaces.


“The structures can densely cover the leaf and may resemble mature, black pustules present on leaves due to infection by rust fungi,” the authors explained. “Lesions with these ascomata may coalesce to cause large areas of blighted leaf tissue, which can be mistaken for saprophytic growth on dead leaf tissue.”


Symptoms and signs of tar spot might also appear on leaf sheaths and husks.


According to Wise and Ruhl, two different fungi, Phyllachora maydis and Monographella maydis, are the causes of tar spot. So far, only Phllachora maydis was discovered in Indiana.


“In areas where this disease is commonly found, infection by Phyllachora maydis is not considered to significantly impact yield, but infections by Monographella maydis can cause economic damage,” the authors said.


In the meantime, Purdue experts will investigate the introduction of the disease into Indiana and determine relevant measures to prevent future outbreaks.

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