Corn Disease Loss Estimates from the United States and Ontario, Canada — 2024

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 environmental conditions, crop production practices, and hybrid susceptibility to disease. 

Plant pathologists representing 29 corn-producing U.S. states and Ontario, Canada, estimated the percent yield losses from corn disease for each participating state or province. These reports account for approximately 15.1 billion bushels, representing 99.2% of the total corn produced in the United States and Ontario in 2024 (Figure 1). The yield loss estimates include root rots, seedling blights, foliar diseases, crazy top, smuts, stalk rots, ear rots, and nematodes. 

This publication summarizes the estimated impact of major diseases on corn production during 2024. 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 specialized experience with disease losses. 

The CDWG determined what corn yield would have been if losses to disease had not occurred using the following formula: 

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

The total bushels lost per disease ([percent loss/100] x yield before estimated loss) for each state or province is then formulated. This does not include mycotoxin contamination, which reduces the quality rather than quantity of grain. 

2024 Conditions and Production 

The United States produced 14.9 billion bushels of corn in 2024, and Ontario produced 0.4 billion bushels. In general, the 2024 cropping season was hot and dry during the grain-filling period. Although some areas received ample rainfall throughout the season, drought conditions were common across most areas, especially in the later part of the season. However, hurricanes may have moved inoculum and vectors from southern to northern regions for diseases such as southern rust and corn stunt.

2024 Disease Losses 

In 2024, disease reduced corn yield by an estimated 6.0 percent across the U. S. and by 3.7 percent in Ontario, resulting in a total estimated loss of 963.4 million bushels. Overall reported percent losses in 2024 were greater than losses reported in the previous two seasons (2022 and 2023), but less than the average loss of 8.4 percent observed between 2012 and 2023. The diseases that resulted in the greatest yield losses were the corn foliar diseases tar spot, southern rust, and northern corn leaf blight, in descending order. Stalk rot and ear rot caused by multiple species of Fusarium were the next greatest causes of estimated yield losses. Table 1 provides yield loss estimates for all diseases, and Figure 3 shows proportionate losses for the top-ranking diseases. As in 2022 and 2023, it was challenging to separate losses caused by crown rot from losses caused by stalk rot. 

Table 1. Estimated corn yield losses (millions of bushels) due to diseases in 29 U.S. corn-producing states and Ontario, Canada, in the 2024 growing season.

¹Includes lance, lesion, root-knot, sting, stubby root, and additional nematode genera; ²Consists entirely of losses caused by corn stunt spiroplasma in Missouri, Oklahoma, and Texas; ³Includes High Plains wheat mosaic virus and corn stunt spiroplasma in South Dakota; and ⁴Detailed notes allowing for the separation of crown rot and other stalk rots were not obtained in all states.

Diseases in the Northern United States 

Tar spot caused the greatest estimated yield reduction in the northern U.S. in 2024 — with 280 million bushels lost. Foliar diseases and diseases caused by Fusarium composed the other top yield reducers, which included southern rust, northern corn leaf blight, Fusarium stalk rot, and Fusarium ear rot, in descending order (see Table 2). During the past five years in this region, tar spot caused either the greatest estimated yield losses out of all diseases (2024, 2022, 2021) or was not even ranked among the top five yield-reducing diseases (2023, 2020). This highlights how dependent foliar disease development is on the occurrence of the appropriate environmental conditions during the growing season.

Table 2. Estimated corn yield losses due to the five most significant diseases in the northernmost U.S. states¹ in 2024.

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

Diseases in the Southern States 

Overall, 2024 losses due to corn diseases in southern states were low and below the 12-year average (2012-2023). Although tar spot was estimated to have caused the greatest yield losses in the southern U.S. states (see Table 3), significant yield losses from tar spot were only reported in Missouri and, to a much lesser extent, in Virginia. In addition, Georgia reported trace yield losses due to tar spot. Estimated losses in the other leaf and aboveground diseases category consisted of corn stunt across three states (Missouri, Oklahoma, Texas). This is the first year since data collection began in 2012 that nematodes that parasitize corn were not amongst the top three yield-reducing diseases.

Table 3. Estimated corn yield losses due to the five most significant diseases in the southernmost U.S. states¹ in 2024.

¹U.S. States include Alabama, Arkansas, Delaware, Georgia, Kentucky, Louisiana, Maryland, Mississippi, Missouri, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, and Virginia; ²Consists of losses caused by corn stunt spiroplasma in Missouri, Oklahoma, and Texas; and ³Includes lance, root-knot, root lesion, sting, stubby root, and additional nematode genera. 

Diseases in Ontario, Canada

The top yield-reducing diseases in Ontario, in 2024 were tar spot, northern corn leaf blight, and nematodes (see Table 4). Tar spot was first detected in Ontario in 2020, and has been estimated to have caused either the greatest yield losses (2021, 2023) or second greatest yield losses (2022) annually after the initial year of discovery.

Table 4. Estimated corn yield losses due to the most significant diseases in Ontario, Canada, in 2024.

¹Only the top three diseases could be differentiated as the next greatest value was a seven way tie among gray leaf spot, common smut, seedling blights, anthracnose stalk rot and top dieback, root rots, common rust, and Carbonum leaf spot; and ²Root lesion nematode.

Mycotoxin Losses 

Plant pathologists estimated that only 0.08 percent and 0.1 percent of the harvested grain in the U.S. and Ontario, Canada, respectively, was contaminated with mycotoxins in 2024. Similarly, low levels were observed in the previous four-year period. Mycotoxin losses are calculated using the USDA-NASS reported production rather than what production would be without other diseases.  

Summary 

The total estimated yield reduction caused by disease in 2024 was greater than estimated losses from the previous two years, but still less than the 12-year average ending in 2023. Only one southern state experienced significant losses from tar spot, and several southern states reported yield losses from Curvularia leaf spot for the first time. Losses caused by corn stunt spiroplasma were recorded for the first time since data collection began in 2012. Hurricane winds were surmised to have enabled travel of certain pathogens either to new locations or to corn-growing areas earlier than normally observed. As in previous years, tar spot continued to expand to new locations along the margins of the existing distribution but did not cause significant yield loss in these areas. 

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 the 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

Data Compilation

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

Authors

Ed Sikora, Auburn University; Travis Faske, University of Arkansas; Ron Meyer, Colorado State University; Alyssa Betts, University of Delaware; Bob Kemerait, University of Georgia; Boris Camiletti, University of Illinois Urbana-Champaign; Darcy Telenko, Purdue University; Alison Robertson, Daren Mueller, and Adam Sisson, Iowa State University; Rodrigo Onofre, Kansas State University; Kiersten Wise, University of Kentucky; Shelly Kerns, Boyd Padgett, and Trey Price, Louisiana State University; Marty Chilvers, Michigan State University; Dean Malvick, University of Minnesota; Tom Allen, Mississippi State University; Mandy Bish, University of Missouri; Tamra Jackson-Ziems, University of Nebraska; Gary Bergstrom, Cornell University; Daisy Ahumada and Ron Heiniger, North Carolina State University; Andrew Friskop, North Dakota State University; Pierce Paul, Ohio State University; Maira Duffeck, Oklahoma State University; Albert Tenuta, Ontario Ministry of Agriculture, Food and Agribusiness; Greg Roth, Alyssa Collins, and Paul Esker, Penn State University; John Mueller and Michael Plumblee, Clemson University; Madalyn Shires, South Dakota State University; Heather Kelly, University of Tennessee; Tom Isakeit and Nolan Anderson, Texas A&M University; David Langston and Yuan Zeng, University of Virginia; and Damon Smith, University of Wisconsin-Madison. 

Reviewers

Dylan Mangel, University of Nebraska-Lincoln and Richard Webster, North Dakota State University.

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

United States Department of Agriculture National Agricultural Statistics Service. Quick Stats Database. Accessed 16 January 2025.

Statistics Canada. Table 32-10-0359-01 Estimated areas, yield, production, average farm price and total farm value of principal field crops, in metric and imperial units. Accessed 16 January 2025.

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 through the Sustainable Canadian Agricultural Partnership (Sustainable CAP), a federal-provincial territorial initiative.