Controlling fire blight without antibiotics in organic apples goal of new USDA project

A team of Michigan State University (MSU) researchers has begun investigating organic methods for controlling fire blight, a devastating apple and pear tree disease.

Fire blight of an apple tree

EAST LANSING, Mich. – A team of Michigan State University (MSU) researchers has begun investigating organic methods for controlling fire blight, a devastating apple and pear tree disease.

The three-year project, under the direction of MSU AgBioResearch plant pathologist George Sundin, is funded by a $464,000 grant from the U.S. Department of Agriculture (USDA). MSU AgBioResearch scientist Matt Grieshop is also involved in the project.

Fire blight is caused by a bacterial pathogen. It infects the flowers of blooming apple and pear trees, spreads into the branches and ultimately kills the tree.

“It’s a serious problem not only in Michigan but worldwide,” said Sundin, MSU professor of plant, soil and microbial sciences. “It’s particularly problematic here in Michigan because, during bloom, we have a humid climate that includes plenty of rain, which contributes to the spread of the disease. One of the things that make fire blight so dangerous is its high degree of infection -- it spreads very quickly.”

In 2000, a fire blight epidemic wiped out over 400,000 apple trees in southwestern Michigan alone, causing an estimated $42 million in damages.

One means of controlling fire blight, an antibiotic chemical called streptomycin, is set to be phased out next year for organic production, Sundin said. This leaves organic growers without a comparable method for protecting fruit trees from the disease.

“Streptomycin is an older antibiotic, but it’s relied on by a lot of organic growers,” he said. “Other options are available, but nothing that’s as effective.”

Conventional growers will continue to have access to other antibiotic sprays, but organic growers are more limited in their options.

“Organic growers are in desperate need of antibiotic alternatives if they are to maintain their organic certification,” said Grieshop, who will assist in the project’s farm experiments and outreach objectives. “Without effective, organically compliant fire blight management tactics, organic apple production will be greatly reduced.”

Sundin’s team will begin a renewed investigation into these other options in an effort to better understand and optimize their use. He said new alternatives are critical for the success of organic apple growers, who do not use the more robust chemical sprays available to conventional growers.

The team will examine several options, including a yeast called Blossom Protect and copper bactericides, which are copper solutions lethal to bacteria.

“Blossom Protect is a yeast that, when applied to the flowers of an apple tree, prevents the fire blight bacteria from entering,” Sundin explained. “We’ve had inconsistent results from it in the past, but our goal now is to study it in greater detail. We need to better understand the mechanism of how it colonizes the flowers and controls fire blight, how it responds to different temperatures and when the right time is to apply it.”

Copper bactericides pose their own challenges.

“They’ve been shown to be effective, but they can also cause russeting -- the formation of blemishes -- on the apples,” Sundin said. “Damaged fruit doesn’t sell, so we need to learn whether applying copper bactericides in lower quantities or at different times can mitigate that.”

Taking a systematic approach, Sundin aims to give organic apple growers the tools they need to protect their crops.

“Understanding how to optimize the use of organically certified materials for fire blight control is really important,” he said. “These materials may seem weaker than streptomycin simply because we’re not using them correctly.”

The project will also help conventional orchards. The team will deliver its results to growers through written and online materials.

Helping organic growers is vital to Michigan’s apple industry, Sundin said.

“Organic produce is becoming more and more important to Michigan consumers,” he said. “There’s no reason for them to have to get their apples from Washington when we can grow them here.”

Having the right techniques to ensure healthy crops is one of the best ways to make that happen.

“We get a lot of disease pressure here because of our climate,” Sundin said. “We need good management tools. That’s something we have for conventional apples but not yet for organics.”

The project will begin this summer and continue through summer 2016. As the research progresses, Sundin said he plans to upload videos to


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