Corn Disease Loss Estimates From the United States and Ontario, Canada — 2020

Corn Disease Loss Estimates From the United States and Ontario, Canada — 2020

CPN-2007-20. Published March 18, 2021. DOI:

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 14.4 billion bushels (98.8 percent) of the total corn produced in the United States and Ontario in 2020 (Figure 1). The yield loss estimates include root rots, seedling blights, foliar diseases, crazy top, smuts, stalk rots, and ear rots.

This publication documents the impact of major diseases on corn production during 2020. 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.

Figure 1. 2020 corn production (in millions of bushels) in 28 U.S. states and Ontario, Canada. 

Figure 2. Fusarium stalk rot was estimated to have reduced yields by almost 93 million bushels in 2020, more than any other disease.

Image: Alison Robertson

2020 Conditions and Production

The United States produced 14.2 billion bushels of corn in 2020, and Ontario, Canada produced 0.4 billion bushels. Portions of the primary corn growing areas of the United States experienced drought conditions during the growing season, reducing the risk from many disease-causing pathogens.

2020 Disease Losses

In 2020, disease reduced corn bushels by 3.9 percent across the United States and by 3.5 percent in Ontario. This is down from an overall 6.8 percent loss experienced in 2019 and 10.9 percent loss experienced in 2018. 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 2020 growing season.

Disease Total US losses (millions of bushels) Total Ontario losses (millions of bushels)
Root Rots and Seedling Blights
Nematodes 75.6 0.7
Root rots 3.3 1.8
Seedling blights 2.8 1.8
Leaf and Aboveground Diseases
Southern rust 91.4 0.0
Gray leaf spot 80.5 0.5
Northern corn leaf blight 56.7 0.9
Bacterial leaf streak 36.5 0.0
Tar spot 12.3 0.0
Goss's wilt 4.6 0.0
Common rust 1.7 0.2
Anthracnose leaf blight 1.1 0.1
Physoderma leaf spot 0.6 0.2
Eyespot 0.5 0.0
Common smut 0.3 1.8
Southern leaf blight 0.2 0.0
Crazy top 0.1 0.0
Holcus spot 0.0 0.0
Carbonum leaf spot 0.0 0.0
Head smut 0.0 0.2
Other leaf and aboveground diseases 0.0 0.0
Stewart's disease 0.0 0.0
Virus -- Maize Dwarf Mosaic  0.0 0.0
Other virus and virus-like diseases 0.0 0.0
Stalk Rots
Fusarium stalk rot 92.5 0.4
Gibberella stalk rot 26.8 0.9
Anthracnose stalk rot and top dieback 22.3 0.7
Diplodia stalk rot 1.9 0.2
Charcoal rot 1.5 0.0
Others stalk rot 1.1 0.0
Bacterial stalk rot 0.0 0.0
Ear Rots
Gibberella ear rot 31.4 1.8
Fusarium ear rot 17.0 0.1
Diplodia ear rot 3.2 0.2
Others ear rot 1.7 0.0
Aspergillus ear rot 0.3 0.0
Mycotoxin contaminated grain 0.24% of harvested grain contaminated 0.10% of harvested grain contaminated


Diseases in the Northern United States

Fusarium stalk rot was the most damaging disease in the northern United States in 2020 — with 91.7 million bushels lost. Southern rust caused the second greatest loss followed by gray leaf spot (see Table 2). Compared to 2019, losses from Fusarium stalk rot and gray leaf spot were much lower in 2020, while southern rust losses were much higher.

Table 2. Estimated corn yield losses due to the seven most significant diseases in the northernmost U.S. states¹ in 2020.

Rank Disease/Pathogen Total losses (millions of bushels)
Northern Region Nation
1 1 Fusarium stalk rot 91.7
2 2 Southern rust 80.7
3 3 Gray leaf spot 71.3
4 4 Nematodes 69.8
5 5 Northern corn leaf blight 52.6
6 6 Bacterial leaf streak 36.5
7 7 Gibberella ear rot 31.1

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

Diseases in Southern States

The foliar diseases southern rust and gray leaf spot caused the greatest damage in the southern United States in 2020, followed by plant-parasitic nematodes and northern corn leaf blight (see Table 3). In 2019, plant-parasitic nematodes and Fusarium stalk rot caused much higher yield loss than foliar diseases.

Table 3. Estimated corn yield losses due to the seven most significant diseases in the southernmost U.S. states¹ in 2020.

Rank Disease/Pathogen Total losses (millions of bushels)
Southern Region Nation
1 2 Southern rust 10.8
2 3 Gray leaf spot 9.1
3 4 Nematodes 5.9
4 5 Northern corn leaf blight 4.1
5 10 Fusarium ear rot 1.4
6 9 Anthracnose stalk rot and top dieback 0.9
7 1 Fusarium stalk rot 0.8

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

Figure 3. Southern rust caused the second greatest yield loss in the northern United States and the greatest yield loss in the southern United States in 2020.

Image: Adam Sisson

Diseases in Ontario, Canada

The top yield-reducing diseases in Ontario were root rots, seeding blights, common smut, Gibberella ear rot followed by northern corn leaf blight, Gibberella and anthracnose stalk rots and plant-parasitic nematodes (see Table 4). In 2020, tar spot was detected for the first time in in southwestern Ontario.

Table 4. Estimated corn yield losses due to the most significant diseases in Ontario, Canada in 2020.

Rank Disease/Pathogen Total losses (millions of bushels)
Ontario, Canada United States
1a 13 Root rots 1.8
1b 15 Seedling blights 1.8
1c 25 Common smut 1.8
1d 7 Gibberella ear rot 1.8
5a 5 Northern corn leaf blight 0.9
5b 8 Gibberella stalk rot 0.9
7a 4 Nematodes 0.7
7b 9 Anthracnose stalk rot and top dieback 0.7


Mycotoxin Losses

In 2020, as in 2019, ear rots were not as common in the United States and Ontario as in 2018. Plant pathologists estimated that only 0.24 percent and 0.10 percent of the harvested grain in the United States and Ontario, Canada, respectfully, was contaminated in 2020.


Environmental conditions were dry during the growing season in many parts of the United States and Ontario in 2020, which affected the presence of and damage from many diseases. Overall, estimated yield losses from corn disease were much less in 2020 than in the preceding two years.


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. 



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


Ed Sikora, Auburn University; Travis Faske, University of Arkansas; Ron Meyer, Colorado State University; Alyssa Koehler, University of Delaware; Bob Kemerait, University of Georgia; Nathan Kleczewski, University of Illinois; Darcy Telenko, Purdue University; Alison Robertson, Iowa State University; Doug Jardine and Rodrigo Onofre, Kansas State University; Carl Bradley, University of Kentucky; Trey Price, Louisiana State University; Marty 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 and Lindsey Thiessen, 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 RothAlyssa Collins, and Paul Esker, Penn State University; John Mueller, 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.


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.

This publication was developed by the Crop Protection Network, a multi-state and international collaboration of university/provincial extension specialists and public/ private professionals that provides unbiased, research-based information to farmers and agricultural personnel.

This information in this publication is only a guide, and the authors assume no liability for practices implemented based on this information. Reference to products in this publication is not intended to be an endorsement to the exclusion of others that may be similar. Individuals using such products assume responsibility for their use in accordance with current directions of the manufacturer.

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