MSU researchers identifying corn tar spot management strategies

A team of MSU scientists is working with regional and national partners to mitigate damage from corn tar spot, a disease that can drastically reduce yields.

Martin Chilvers, a plant pathologist at MSU.

EAST LANSING, Mich. — A successful growing season for farmers requires a delicate balance. Take water as an example. Not enough, and plant development will be stunted. Too much can saturate the soil, while the lingering moisture lays the foundation for disease.

Since 2016, Michigan corn growers have witnessed firsthand how years with wet conditions are particularly problematic for tar spot, a fungal disease that was discovered in the state that year.

Prior to 2015, tar spot was mostly found in Central and South America. Since then, however, the pathogen has taken hold across most of the U.S. corn belt — 19 total states thus far — and Ontario, Canada.

Tar spot presents as small, black lesions on leaves, which quickly begin to destroy plant tissue. 2018 and 2021 have been tar spot’s most prolific seasons in Michigan. Plentiful rain, morning dew and fog kept leaves wet, allowing the pathogen to thrive. Drier years such as 2022 saw far less incidence of disease.

Once tar spot has infested a field, mitigating damage becomes incredibly difficult. Previous research has shown that spread is rapid if mismanaged, from a few dots on one plant’s leaves to engulfing an entire field in less than three weeks.

Martin Chilvers, an associate professor in the Michigan State University Department of Plant, Soil and Microbial Sciences, has been working with Michigan corn growers on management strategies.

“This is a devastating disease for growers, not only in Michigan but everywhere it’s present,” said Chilvers, whose research is supported in part by MSU AgBioResearch. “In 2018, for example, we saw epidemic levels in areas of the state. Some growers were losing 50 to 100 bushels per acre. National estimates put losses at 183 million bushels. There were similar losses in 2021. This is something we need to figure out, and we’re doing that by studying the disease on a number of fronts.”

Tar spot on corn leaves. Photo courtesy of Martin Chilvers.

Chilvers has partnered with colleagues from MSU, other universities, agricultural commodity organizations and companies to perform an array of tests on fungicide efficacy and timing, hybrid resistance, planting density, and spore trapping. The research teams have leaned on his experience with new diseases in both corn and soybean cropping systems.

“Dr. Chilvers is extremely knowledgeable and an excellent educator,” said Kristin Poley, research manager for the Corn Marketing Program of Michigan (CMPM). “He is able to concisely and distinctly articulate research findings to any audience, and CMPM has always appreciated Dr. Chilvers’ dedication to farmers through research, events and publications. Most importantly, Dr. Chilvers is quick to turn research results into actionable recommendations for management of tar spot, which is exactly what Michigan farmers need when a new disease arrives.”

Alongside the CMPM, one of the most significant sources of support for early tar spot research at MSU came from Project GREEEN (Generating Research and Extension to Meet Economic and Environmental Needs). The initiative funded many of the field trials that produced the first information upon which grower recommendations have been built.

“Weather is the key driver to tar spot development,” Chilvers said. “We know that much for certain, so most of our recommendations are based on the work we’ve done around that idea, and some are common sense or concepts borrowed from the management of other diseases. We are still trying to put data sets together to better inform or demonstrate management implications.”

Putting solutions in growers’ hands

When any new disease starts affecting operations, grower anxiety rises. It’s Chilvers’ job to help them navigate through the initial concerns and prepare them to deal with the challenge. Poley said Chilvers has been a vital part of the research and outreach processes.

“We’ve learned a lot of valuable information on the environmental conditions that lead to disease onset, and the effectiveness and profitability of various management strategies – especially as it relates to fungicide products and timing of applications – as a direct result of Dr. Chilvers’ research,” Poley said. “Most importantly, we’ve been able to compare each of these insights year over year to further refine our management recommendations.”

A series of tips and tools have been created to assist growers, from a smartphone app to online resources such as fungicide efficacy tables and variety selection suggestions. All of this information is shared via extension services at partner universities and on the Crop Protection Network website, a joint effort of land-grant universities to distribute research findings.

On the technology side — using data from MSU researchers, among others — Chilvers’ colleague at the University of Wisconsin-Madison, Damon Smith, produced a disease risk prediction algorithm available for smart phones called Tarspotter.

The app uses GPS coordinates to identify if the weather in a given area has been friendly to tar spot fungus development. Based on future weather predictions, crop development stage and characteristics, a disease forecast is generated.

More recently, led by graduate student Emily Roggenkamp in Chilvers’ lab, the team has developed a real-time PCR diagnostic technique that detects tar spot quickly, which will be shared with collaborators to use in future growing seasons in Michigan and beyond. Chilvers and his team have also assembled a high-quality genome sequence of the tar spot pathogen, Phyllachora maydis

“The diagnostic tool is obviously important for us in identification of the disease quickly, and it can be paired with spore traps to detect the fungus prior to disease symptoms,” Chilvers said. “The genome sequence is invaluable because it helps us potentially understand more about infection, resistance and biology of the pathogen. This information allows us to apply fungicides at the most ideal times, learn about the conditions that lead to disease, and even develop resistant varieties.”

Looking toward the future

Addie Thomspon formal
Addie Thompson, assistant professor of maize genetics and genomics.

Chilvers is part of a relatively new project led by Addie Thompson, an assistant professor of maize genetics and genomics in the MSU Department of Plant, Soil and Microbial Sciences, looking at tar spot resistance.

The group was funded in summer 2022 by a $590,000 grant from the U.S. Department of Agriculture’s (USDA) National Institute of Food and Agriculture, building on previous USDA-funded work, the Great Lakes Tar Spot Initiative.

The project is focusing on characterizing the phenolic compounds that accumulate in corn in response to tar spot infection. Phenolic compounds are essential to plants’ defense from pests and diseases. Researchers will then test and validate previously identified resistance genes. 

Using this information, along with remote sensing data collected through multispectral and hyperspectral imaging, the group will create predictive models on tar spot severity and the relationship to phenolic compound accumulation. This can ideally help detect early onset of the disease.

“Understanding the relationship between compound accumulation and resistance will enable development of new varieties of corn that are less reliant on pesticides,” Thompson said. “Results will be highly applicable to breeders and growers, which is why this project is innovative and timely as this disease spreads at alarming rates each year throughout the upper Midwest.”

Additionally, Chilvers received funding in 2022 for a project through the Michigan Alliance for Animal Agriculture (M-AAA), an initiative that brings together MSU and animal agriculture industries. The research will address tar spot in corn silage, which is used for animal feed on many Michigan dairy farms.  

Tar spot negatively affects corn silage by rendering it too dry, reducing quality and zapping nutrient content. This leads to less productive cows and lower profitability for producers. Working with dairy farmers and the Michigan Milk Producers Association, Chilvers will conduct variety susceptibility trials across hybrids, as well as fungicide efficacy, fungicide timing and silage chop timing experiments.

“Just as Project GREEEN does for plant agriculture, the M-AAA is a very important funding mechanism to solve problems in Michigan animal agriculture,” Chilvers said. “I’m very grateful for the opportunity to do research that cuts across a wide range of industries.”

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