Corn Disease Loss Estimates from the United States and Ontario, Canada — 2025

Corn diseases annually reduce yield in the United States and Canada. Diseases of importance vary from year to year, because of 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 their state or province. These reports account for approximately 17.3 billion bushels, representing 99.2% of the total corn produced in the United States and Ontario in 2025 (Figure 1). The yield loss estimates include plant diseases that can be more broadly categorized as root rots, seedling blights, foliar diseases, smuts, stalk rots, ear rots, and nematodes. 

This publication summarizes the estimated impact of major diseases on corn production during 2025. 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 as a result of each 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.

2025 Production and Conditions

The United States produced 17.0 billion bushels of corn in 2025, and Ontario produced 0.4 billion bushels. Corn production in the U.S. during 2025 was a record high, eclipsing the next greatest production year (2023) by nearly 1.7 billion bushels. In general, near normal rainfall and above average temperatures across corn growing regions for the 2025 calendar year. However, from 1 May through 30 September, precipitation was highly dependent upon location (Figure 2). Some regions experienced 10+ inches of precipitation above normal, while multiple states experienced drought conditions Temperatures were several degrees above normal for most corn growing states (Figure 3). The National Oceanic and Atmospheric Administration reported record humidity and record high overnight temperatures from mid-June through late July in parts of the Midwest U.S.

Environmental conditions in 2025, along with additional factors, contributed to a southern rust epidemic in major corn producing states (Figures 4 and 5). Low commodity prices reduced fungicide applications on fields in the southern U.S. and increased acreage planted to corn in southern states likely contributed to elevated inoculum of the fungus that causes southern rust. This inoculum was able to spread via wind to northern states. Severe yield loss occurred when environmental conditions promoted repeated cycles of southern rust, especially in fields that did not receive a timely fungicide application.

2025 Disease Losses

In 2025, diseases reduced corn yield by an estimated 7.0 percent across the U.S. and by 2.2 percent in Ontario, resulting in a total estimated loss of 1.3 billion bushels. Overall reported percent losses in 2025 were the greatest since 2018, but slightly lower than the average loss of 7.7 percent observed between 2012 and 2024. The diseases that resulted in the greatest yield losses were the corn foliar diseases southern rust, tar spot, and northern corn leaf blight, in descending order. Anthracnose stalk rot and top dieback, Fusarium stalk rot, and Fusarium ear rot were the next greatest causes of estimated yield losses. Table 1 provides yield loss estimates for all diseases, and Figure 6 shows proportionate losses for the top-ranking diseases. As in previous years, it was challenging to separate losses caused by crown rot from losses caused by stalk rot. 

Table 1. Estimated corn yield losses (thousands of bushels) due to diseases in 29 U.S. corn-producing states and Ontario, Canada, in the 2025 growing season.

¹Includes lance, lesion, root-knot, sting, stubby root, and additional nematode genera; ²Detailed notes allowing for the separation of crown rot and other stalk rots were not obtained in all states.

Diseases in the Northern United States

Southern rust caused the greatest estimated yield reduction in the northern U.S. in 2025 – with 490.1 million bushels lost. Tar spot, northern corn leaf blight, anthracnose stalk rot and top dieback, and Fusarium stalk rot were the next greatest causes of yield loss, in descending order (Table 2). Curvularia leaf spot was detected in most of the North Central U.S. states for the first time in 2025.

Table 2. Estimated corn yield losses due to the five most significant diseases in the northernmost U.S. states¹ in 2025.

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 United States

The total estimated percent loss due to corn diseases in southern states in 2025 was below the average of the 13 years of existing data (2012-2024). However, bushel losses were the second greatest ever reported, eclipsed only by losses from 2016. Southern rust caused the greatest estimated yield losses in southern states by a wide margin (Table 3). In fact, losses from southern rust were greater than all other diseases combined in 2025. The next greatest losses were caused by anthracnose stalk rot and top dieback, Fusarium stalk rot, tar spot, and gray leaf spot. It is important to note that yield losses from tar spot were primarily reported in Missouri, with trace yield losses from tar spot reported in Georgia and South Carolina. No additional southern states reported yield losses from tar spot. The relative impact of plant parasitic nematodes continued to decline in 2025, which was the first year these organisms did not appear among the top five greatest causes of yield loss since data collection began in 2012.

Table 3. Estimated corn yield losses due to the five most significant diseases in the southernmost U.S. states¹ in 2025.

¹U.S. states include Alabama, Arkansas, Delaware, Georgia, Kentucky, Louisiana, Maryland, Mississippi, Missouri, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, and Virginia; ²Fusarium stalk rot caused greater estimated yield loss than tar spot; however, rounding to the nearest thousand results in the same number. 

Diseases in Ontario, Canada

The top yield-reducing diseases in Ontario in 2025 were northern corn leaf blight, tar spot, and nematodes (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, and 2024) or second greatest yield losses (2022 and 2025) 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 six way tie among anthracnose stalk rot and top dieback, gray leaf spot, Gibberella ear rot, seedling blights, common rust, and common smut; ²Root lesion nematode.

Mycotoxin Losses

Plant pathologists estimated that only 0.2 percent and 0.1 percent of the harvested grain in the U.S. and Ontario, Canada, respectively, was contaminated with mycotoxins in 2025. Similarly, low levels were observed over the previous five-year period. Mycotoxin losses are calculated using the USDA-NASS reported production rather than what production would be without other diseases.

Summary

Disease reduced corn yield in 2025 by an estimated 7.0 percent across the U.S. (Figure 7) and by 2.2 percent in Ontario, resulting in a total estimated loss of 1.3 billion bushels. The total estimated yield reduction caused by disease was largely driven by the southern rust epidemic. Losses attributed to southern rust were greater than the next four causes of yield loss combined (tar spot, northern corn leaf blight, anthracnose stalk rot and top dieback, and Fusarium stalk rot). Severe foliar disease may also contribute to increased stalk rot as corn plants withdraw carbohydrates from stalk tissue to fill ears when disease damaged leaf tissues can no longer photosynthesize. However, this depends on the growth stage when severe disease occurs. Additionally, the cost of fungicide application efforts to manage southern rust were likely considerable, especially where multiple applications of fungicide occurred. These management costs contributed to already high corn production costs coinciding with low commodity prices, further reducing profit margins for farmers. Thus, the economic impact of southern rust goes well beyond mere yield losses attributed to this disease. 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 losses 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.

Acknowledgements

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 Wade Webster, North Dakota State University.

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

Iowa Environmental Mesonet. Automated Data Plotter. Plot #97. Accessed 27 January 2026.

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 20 January 2026.

United States Department of Agriculture National Agricultural Statistics Service. Quick Stats Database. Accessed 20 January 2026.

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, Support was also provided by the Indiana Corn Marketing Council and the Louisiana Soybean and Grain Research and Promotion Board.

How to cite: Sikora, E., Faske, T., Meyer, R., Betts, A., Kemerait, B., Camiletti, B., Telenko, D., Robertson, A., Mueller, D., Sisson, A., Onofre, R., Wise, K., Kerns, S., Padgett, B., Price, T., Chilvers, M., Malvick, D., Allen, T., Bish, M., Jackson-Ziems, T., Bergstrom, G., Ahumada, D., Heiniger, R., Fiskop, A., Paul, P., Duffeck, M., Tenuta, A., Roth, G., Collins, A., Esker, P., Mueller, J., Plumblee, M., Shires, M., Kelly, H., Isakeit, T., Anderson, N., Langston, D., Zeng, Y., Smith, D. 2026. Corn Disease Loss Estimates from the United States and Ontario, Canada — 2025. Crop Protection Network. CPN-2007-25. https://cropprotectionnetwork.org/publications/corn-disease-loss-estimates-from-the-united-states-and-ontario-canada-2025.