A Farmer’s Guide to Corn Diseases

Corn (Zea mays L.) has evolved into a major grain crop that is essential for food and fuel in the United States and Canada. The United States is the world’s number-one producer of corn, growing tens of billions of bushels annually. Record corn yields have made corn a profitable and important field crop in North America. 


When a crop has high value and demand, protecting its yield potential is essential to reaping the greatest economic returns. Doing so means keeping the crop as healthy as possible—a goal that involves disease management. The cornerstone of effective disease management is accurate disease diagnosis. However, as farmers become more aware of how diseases affect corn yields, they may be overwhelmed by the number of diseases that can be present on corn and struggle to diagnose and manage diseases of importance.


The purpose of A Farmer’s Guide to Corn Diseases is to provide an overview of the corn diseases that occur in the United States and Canada, with an emphasis on diagnosing diseases in the field setting. This guide explains the factors that make plants unhealthy, including plant pathogens. It also presents brief summaries of prevalent corn diseases. Each disease summary includes sections that describe symptoms and signs of the disease, identify diseases and disorders with similar symptoms and signs, state the conditions that favor disease development, and review basic management options.


The information presented for each disease is based on Compendium of Corn Diseases, Fourth Edition, edited by Gary P. Munkvold and Donald G. White (American Phytopathological Society, 2016). However, additional information is also provided to aid in diagnosis—for instance, key diagnostic terms and disease distribution maps. A Farmer’s Guide to Corn Diseases is not intended to provide an exhaustive discussion of every disease that occurs on corn, and management recommendations are intentionally generalized to encourage readers to contact state and provincial Extension personnel or crop management specialists for region-specific management options.


Although this guide focuses on corn diseases that occur in the United States and Canada, many other diseases have global importance. Some of these diseases are addressed in Chapter 9. Farmers should be aware of disease issues that may be of future importance to the United States and Canada.


Producing A Farmer’s Guide to Corn Diseases truly has been a collaborative effort. Fifty-nine contributors from more than 25 universities, agencies, and companies were consulted for their expertise with particular diseases. These contributors dedicated their time to editing sections, supplying images, and providing input on the development and direction of this book. The result is the first comprehensive overview of corn diseases across the United States and Canada written with an audience of farmers in mind.


As corn production practices advance and as environments change, so will the disease issues of importance. This guide is meant to be an evolving reference, and making updates and additions will be critical to maintaining its relevance. We encourage readers to offer feedback and suggestions to help improve this book, as we aim to improve the quality of disease references available to individuals involved in corn production.


Quantity discounts are available for easy distribution to field representatives and other experts at your organization; VIP clients/customers in the corn industry; colleagues in state and county Extension agencies; and fellow researchers and diagnosticians at your institution.