Thursday, October 1, 2015

Tar Spot Appears in the Midwest

Tar Spot, a fungal disease in corn typically found in Mexico, South America and the Caribbean has been spotted in fields near the Indiana-Ohio border. While no threat for growers this year, it could cause problems in next year's crop if the fungus survives the winter.

This corn disease is not only new to Indiana and Illinois, where it was first reported, but its appearance is a first in the U.S., according to Pierce Paul, a corn and small grain Extension specialist with the College of Food, Agricultural, and Environmental Sciences at The Ohio State University. It may have been transported to the Midwest earlier this season by Tropical Storm Bill.

“We don’t want to cause a panic, but we do want to raise awareness of the issue and let growers know that this disease is out there,” Paul said.

Tar spot begins as oval to irregular bleached to brown lesions on leaves in which black spore-producing structures are formed. Affected areas of the leaf will have a rough or bumpy feel to the touch. Signs of tar spot can also appear on leaf sheaths and husks.

“Because tar spot is generally considered a tropical disease, it’s unlikely that the fungus will survive the harsh Midwest winter to become established here,” Paul said. “We’ll just have to wait and see and do more research on the disease in the Midwest.”

While most corn growers are either harvesting corn now or their crops are in the drying down stage, the disease is still detectable on dry, senescent leaves, he said. Growers who suspect they’ve found it in their fields can send samples to Pierce Paul at OARDC, 1680 Madison Ave., Wooster, OH 44691, to have the samples lab tested to determine which fungus — Phyllachora maydis or Monographella maydis — may be present.

“At this point, only P. maydis-infected plants have been found,” he said. “Both fungi would have to be found before substantial yield loss occurs.

“Growers who find tar spot in their fields may want to take note of the hybrid they’ve used this year and avoid using that same hybrid next year just in case the fungus survives the winter.”

Source: Ohio State University Extension

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