Corn leaf samples from three northern Illinois counties have been confirmed positive for the fungus Phyllachora
The Illinois Department of Agriculture announced news of the disease yesterday. Megan
The samples were collected from commercial fields by Monsanto breeders and pathologists and sent to Kiersten Wise of Purdue University in response to her inquiry for samples and distribution information of the tar spot pathogen. Wise and Purdue Plant Clinic director Gail Ruhl initially identified the pathogen, which is new to the United States, almost two weeks ago and submitted confirmation samples to the USDA.
Bissonnette said upon receipt of the Illinois samples, they diagnosed the fungus, contacted the University of Illinois Plant Clinic, and submitted the Illinois samples to the USDA for confirmation.
“Scouting for the disease has been active in Illinois,” Bissonnette said. “Jennifer Chaky of Pioneer Plant Diagnostic Clinic also has samples from Bureau County diagnosed with tar spot. The University of Illinois Plant Clinic has also diagnosed LaSalle county samples from Russ Higgins, U of I Extension agronomist in northern Illinois.”
Tar spot has distinctive symptoms. The fungal fruiting body, called an ascomata, looks like a spot of tar on the leaf. Lesions are black and sunken oval or circular. They can be small flecks of about 1/64 of an inch up to about 5/64 of an inch. The lesions can merge together to produce an affected area up to 3/8 of an inch. “If you run your finger across the leaf you will feel tiny bumps,” Bissonnette explained.
Prior to the Indiana finding, tar spot was known to occur only in cool humid areas at high elevations in Latin America.
“There are actually two fungi that cause tar spot disease on corn: Phyllachora
To date only one of the pathogens, Phyllachora
Growers who suspect tar spot are encouraged to submit a sample to the University of Illinois Plant Clinic. “We would like to get a comprehensive idea of distribution in the state,” Bissonnette said.
For more information on tar spot of corn, please see the USDA-ARS Diagnostic Fact Sheet at http://nt.ars-grin.gov/taxadescriptions/factsheets/index.cfm?thisapp=Phyllachoramaydis.
Source: University of Illinois