Tar Spot of Corn

Tar Spot Preface and Introduction

Tar Spot of Corn

CPN 2015. Published March 16, 2021. DOI: doi.org/10.31274/cpn-20201214-2

Darcy Telenko, Purdue University; Martin Chilvers, Michigan State University; Nathan Kleczewski, University of Illinois; Daren Mueller, Iowa State University; Diane Plewa, University of Illinois; Alison Robertson, Iowa State University; Damon Smith, University of Wisconsin; Adam Sisson, Iowa State University; Albert Tenuta, Ontario Ministry of Agriculture, Food and Rural Affairs; and Kiersten Wise, University of Kentucky.

Tar spot of corn is a new and emerging disease in the Midwestern United States. This disease is caused by the fungus Phyllachora maydis. Although there are many species of Phyllachora that infect various grass species, P. maydis is only known to infect corn. It was first identified in Illinois and Indiana in 2015. As of 2020, tar spot has been confirmed in 10 states in the U.S. including Florida, Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Ohio, Pennsylvania, and Wisconsin, as well as Ontario, Canada.

Significant yield impact was first noted in 2018 in Illinois, Indiana, Michigan, and Wisconsin, with estimated yield losses ranging from 20 to 60 bu/A in regions experiencing the epidemic. 

Tar spot has become an annual problem in regions with favorable environmental conditions which include moderate temperatures and high relative humidity and prolonged leaf wetness. 

Characteristic tar spot symptoms on corn foliar tissue. Image: Darcy Telenko

Live Tar Spot Distribution Map

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