Study tracks four years of disease loss in corn


Research conducted in the United States and Canada should give growers a better idea of what diseases they’re facing 

A new study involving the collaboration of more than 25 universities offers farmers and breeders new data to assess what diseases are affecting corn production in Canada and the United States.

Plant pathologists with the Corn Disease Working Group at universities across 26 corn-producing states and in Ontario gathered data over four years to provide estimates of yield losses from disease at the end of each growing season from 2016 through 2019.

While estimated losses from each disease varied greatly by state, province and year, two pathogens showed significant damage. They were gray leaf spot, which caused the greatest estimated yield loss in parts of the northern U.S. and Ontario in all years except 2019, and fusarium stalk rot, which also significantly reduced yield.

In the northern U.S. a relatively new disease, tar spot, caused substantial losses in 2018 and 2019. Gray leaf spot and southern rust caused the greatest estimated yield losses in the southern United States.

Researchers also noticed year-to-year fluctuations.

Daren Mueller, associate professor and extension plant pathologist at Iowa State University, said the study was initiated to understand the level of damage caused by corn diseases.

“I am not overly surprised by the levels of damage, but I do find it interesting the fluctuations from year to year.”

According to the report, the estimated corn production losses per year across all states and Ontario combined were 10.8, 6.7, 10.9, and 6.8 percent for 2016, 2017, 2018, and 2019, respectively. It differed greatly by state from negligible yield loss in Mississippi in 2017 to 22.8 per cent in Ohio in 2016.

According to the report published in Plant Health Progress, the survey represents 98 percent of the total corn produced in the U.S. and Ontario from 2016 to 2019.

Total corn production was 59.1 billion bushels (1.5 billion tonnes) valued at US$210.7 billion.

Even if only the lowest annual yield loss of two percent was realized, that loss over the period would total nearly 1.2 billion bushels, or 30.5 million tonnes, representing more than US$4.2 billion in lost revenue.

Total corn production across the survey area ranged from a low of 13.8 billion bushels in 2019 to a high of 15.2 billion bushels in 2016. Individual state and provincial production values varied widely from year to year.

But understanding what drives losses from diseases can be challenging.

“The easiest way to describe it is that the environment plays a role, the hybrids planted by farmers, and how well the pathogen survived from previous years,” said Mueller.

States and Ontario were divided into southern and northern geographic regions. A list of diseases was provided to plant pathologists annually. Respondents were asked to estimate percent losses for each disease and to include information about any relevant diseases not listed. They used various methods to estimate yield losses and most relied on more than one method to obtain the most accurate estimate possible.

Estimates were based on data from sources such as statewide or provincial disease surveys, feedback from universities, industry and farmer representatives, plant disease diagnostic laboratory samples, research plots, personal experience with disease losses, and other methods.

Disease loss estimates were primarily for hybrid corn harvested for grain. Estimates for losses from bacterial leaf streak and tar spot began in 2017 and 2018 respectively as these diseases became more important risks to corn production.

Mueller said that new diseases are emerging but whether they are being driven by climate change and greater variability in extreme weather events is unclear. However, wet or delayed harvest conditions in 2018 resulted in about 2.5 billion bushels of grain contaminated with mycotoxins, metabolites caused by certain fungi moulds and that contain toxic chemicals.

“I think we are certainly seeing new diseases such as tar spot and bacterial leaf streak,” he said. “But I am not sure if it is related to the introduction of the pathogen or changes in climate. Probably both play a role, but it is too early to tell.”

The data provides breeders and farmers a chance to look at hybrid varieties susceptible to diseases in their region and consider adjustments to breeding protocols. The data will also help scientists, government agencies and educators to inform and prioritize research, policy, and educational efforts in corn pathology and disease management.