Corn Disease Loss Estimates From the United States and Ontario, Canada — 2021

Corn diseases annually reduce yield in the United States and Canada. Diseases of importance vary from year to year, and diseases that affect yield are based on many factors, including weather conditions, crop production practices, and hybrid selection and susceptibility to disease.

Plant pathologists representing 28 corn-producing U.S. states and Ontario, Canada, estimated the percent yield loss from corn disease in their states and province. These reports account for 15.3 billion bushels (98.9 percent) of the total corn produced in the United States and Ontario in 2021 (Figure 1). The yield loss estimates include root rots, seedling blights, foliar diseases, crazy top, smuts, stalk rots, ear rots, and nematodes.

This publication documents the impact of major diseases on corn production during 2021. The Corn Disease Working Group (CDWG) revises disease loss estimates annually. It is important to note that methods for estimat­ing disease loss vary by state or province. The estimates may be based on statewide disease surveys; feedback from university extension, industry, and farmer represen­tatives; and personal experience with disease losses.

The CDWG determined disease loss values based on yield before estimated losses for each state or province using this formula:

(harvested bushels/[{100 – percent estimated disease loss}/100])

The CDWG then formulated total bushels lost per disease ([percent loss/100] x yield before estimated loss) for each state or province.

2021 Conditions and Production

The United States produced 15.1 billion bushels of corn in 2021, and Ontario, Canada produced 0.4 billion bushels. The continental U.S. experienced above average temperatures in 2021. Many major weather or climate events occurred in 2021 in the U.S., including a derecho, drought, tornadoes, and severe storms. Much of the western U.S. experienced below average precipitation, reducing the risk from many disease-causing pathogens in states such as Iowa; above average levels of precipitation occurred across many eastern U.S. states.

2021 Disease Losses

In 2021, disease reduced corn bushels by 6.5 percent across the United States and by 4.6 percent in Ontario. This is up from an overall 3.9 percent in 2020, and corresponds more closely with the overall 6.8 percent loss experienced in 2019. In 2018, an overall 10.9 percent loss occurred. Most of this increase in disease loss in 2021 compared to 2020 was due to severe outbreaks of tar spot in Illinois, Indiana, Michigan, and Wisconsin. Four of the top five yield reducing diseases in 2021 were foliar diseases; notably, tar spot reduced yield more than the next greatest yield-reducing disease by a wide margin. Table 1 provides yield loss estimates for all diseases.

Table 1. Estimated corn yield losses (millions of bushels) due to diseases in 28 U.S. corn-producing states and Ontario, Canada in the 2021 growing season.

Diseases in the Northern United States

Tar spot was the most damaging disease in the northern United States in 2021 — with 228.5 million bushels lost. Fusarium stalk rot caused the second greatest loss followed by gray leaf spot (see Table 2). Yield reductions from tar spot were much higher in 2021 than in 2020, and more closely matched the losses from tar spot that occurred in 2018.

Table 2. Estimated corn yield losses due to the five most significant diseases in the northernmost U.S. states¹ in 2021.

¹ U.S. States include Colorado, Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Nebras­ka, New York, North Dakota, Ohio, Pennsylvania, South Dakota, and Wisconsin.

Diseases in Southern States

Overall, losses due to corn diseases in southern states were low in 2021. The foliar diseases southern rust and gray leaf spot caused the greatest damage in the southern United States in 2021, followed by plant-parasitic nematodes and northern corn leaf blight (see Table 3). The top four yield-reducing diseases were the same as in 2020, while plant-parasitic nematodes and Fusarium stalk rot caused much higher yield loss than foliar diseases in 2019. Tar spot was reported for the first time in 2021 in several southern states, and although yield loss was not reported in most of these states, tar spot did reduce yield in Missouri and Georgia.

Table 3. Estimated corn yield losses due to the five most significant diseases in the southernmost U.S. states¹ in 2021.

¹ Alabama, Arkansas, Delaware, Georgia, Kentucky, Louisiana, Maryland, Mississippi, Missouri, North Carolina, South Carolina, Tennessee, Texas, and Virginia. 

Diseases in Ontario, Canada

The top yield-reducing diseases in Ontario were tar spot, root rots, seeding blights, and northern corn leaf blight (see Table 4). Tar spot was detected for the first time in in southwestern Ontario in 2020, and caused the greatest yield loss among all diseases in 2021.

Table 4. Estimated corn yield losses due to the most significant diseases in Ontario, Canada in 2021.

Mycotoxin Losses

Plant pathologists estimated that only 0.17 percent and 0.10 percent of the harvested grain in the United States and Ontario, Canada, respectfully, was contaminated with mycotoxins in 2021. Similarly low levels were observed during 2020 and 2019.

Summary

Although total yield reduction caused by disease in 2021 was 321.5 million bushels below the average reduction observed from 2012 to 2020, individual states experienced significant disease losses where conditions were favorable for tar spot. Environmental conditions were dry during the growing season in parts of the United States and Ontario in 2021, which affected the presence of and damage from many diseases. Tar spot was observed in several new states in 2020, and is growing in importance in both the northern and southern United States, as well as in Canada. Curvularia leaf spot was reported from multiple states, indicating this disease is becoming more widespread since initially observed in the United States in Louisiana in 2017. At this time, however, it is not yet causing appreciable yield loss.

Disclaimer

The disease loss estimates in this publication were provided by members of the Corn Disease Working Group (CDWG). This information is only a guide. The values in this publication are not intended to be exact estimates of corn yield losses due to diseases. The members of the CDWG used the most appropriate means available to estimate disease losses and assume no liability resulting from the use of these estimates. 

Values reported in this document were accurate as of publication date and do not reflect corrections or updates occurring since that time. For the most up-to-date values and additional information on yield and economic losses due to diseases, see the Field Crop Disease Loss Calculator.

Acknowledgments

Authors

Daren Mueller, Iowa State University; Kiersten Wise, University of Kentucky; and Adam Sisson, Iowa State University

Contributors

Ed Sikora, Auburn University; Travis Faske, University of Arkansas; Ron Meyer, Colorado State University; Alyssa Koehler, University of Delaware; Bob Kemerait, University of Georgia; Chelsea Harbach and Nathan Kleczewski, University of Illinois; Darcy Telenko, Purdue University; Alison Robertson, Iowa State University; Rodrigo Onofre, Kansas State University; Trey Price, Louisiana State University; Martin Chilvers, Michigan State University; Dean Malvick, University of Minnesota; Tom Allen, Mississippi State University; Kaitlyn Bissonnette, University of Missouri; Tamra Jackson-Ziems, University of Nebraska; Gary Bergstrom, Cornell University; Ron Heiniger, North Carolina State University; Andrew Friskop, North Dakota State University; Pierce Paul, Ohio State University; Albert Tenuta, Ontario Ministry of Agriculture, Food and Rural Affairs; Greg Roth, Alyssa Collins, and Paul Esker, Penn State University; John Mueller and Michael Plumblee, Clemson University; Emmanuel Byamukama, South Dakota State University; Heather Kelly, University of Tennessee; Tom Isakeit, Texas A&M University; David Langston, University of Virginia; and Damon Smith, University of Wisconsin-Madison. 

Production data from the United States Department of Agriculture-National Agriculture Statistics Service and the Ontario Ministry of Agriculture Food and Rural Affairs. Climate information from the National Oceanic and Atmospheric Administration-National Center for Environmental Information.

Sponsors

In addition to support from United States Department of Agriculture - National Institute of Food and Agriculture, this project was funded in part through the National Corn Growers Association and the Grain Farmers of Ontario.