State wants federal OK on chemical to fight apple blight

February 5, 2012
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LANSING — The state is seeking federal permission to use an unregistered pesticide on up to 10,000 acres of apples trees that are susceptible to a deadly disease.

The bacteria causing the disease have grown resistant to current treatments, agricultural experts say.

The spray-on fungus killer, an antibiotic called kasugamycin, would control fire blight, which has been on the uptick in Michigan orchards the past few springs.

The bacterial disease attacks apple and pear trees’ blossoms, shoots and limbs. Branches, leaves and trees look scorched when infected. The disease is sporadic, hard to control and usually attacks in the spring.

“Fire blight is just so detrimental,” said Nikki Rothwell, a district horticulturist with the Northwest Michigan Horticulture Research Center in Traverse City. “It comes during the bloom. Bacteria build up in flowers, and rain can flush it out and cause an infection.”

For years apple trees have been treated with a different antibiotic, streptomycin, but the bacteria are growing resistant to it. Kasugamycin would kill the bacteria.

“We used streptomycin for many years and had great success,” Rothwell said. “But we’ve gone out and sampled a lot of orchards, and in most places it’s no longer doing its job.”

There is worry that, if untreated, fire blight could decimate the state’s apple production.

Michigan grows more apples than all but two other states, producing more than 590 million pounds in 2010. The crop was worth about $104 million at the farm level, and the Michigan Apple Committee estimates its economic impact at $700 million a year.

Jennifer Holton, an Agriculture Department public information officer, said, “In Michigan a lot of apples are grown at very high densities, so it’s feasible for fire blight to wipe out an entire orchard in one season.”

The department has requested and received a federal exemption the past three years, Holton said.

The current request entails up to three applications of the antibiotic on as many as 10,000 acres between April 1 and May 31. The maximum amount sprayed will be approximately 30,000 gallons.

Fire blight primarily affects Southwest and Northwest Michigan. With federal permission, the fungicide will be used only in 10 counties in those regions.

The top five apple producing counties are Kent, Berrien, Van Buren, Oceana and Ottawa, all of which would be covered under the exemption.

Although fire blight has touched farms throughout the Great Lakes region, no other states have requested use of kasugamycin.

Registered pesticides are those that the Environmental Protection Agency has tested for human and environmental effects, after which the agency provides directions for use. Kasugamycin isn’t an EPA-registered pesticide, but an agency primer doesn’t consider it toxic or cancer-causing.

The EPA would not comment on why kasugamycin isn’t registered. Rothwell said she believes the reason is a fear of approving antibiotic fungicides.

Bacteria evolve and grow resistant to fungicides, which causes concern that the bacteria could infect humans and resist antibiotics, she said.

“I think there’s hesitancy about giving people carte blanche to use it because of bacterial resistance,” Rothwell said. “Bacteria don’t care if it’s a tree or a person — the resistance can be passed.”

However, there is less worry about kasugamycin because it isn’t used in human medicine, Rothwell said.

According to David Wade, the director of the division of environmental health at the Department of Community Health, the method and timing of the fungicide spraying renders it almost entirely harmless for people.

“The application precedes harvest by quite a large amount of time,” Wade said. “By the time apples are harvested, the fungicide is below levels of detection.”

Wade said for the exemption to be granted, the EPA must determine that it poses an insignificant risk to humans.

But safe doesn’t always mean successful. The bacteria could eventually grow resistant to the new fungicide, as it did with the old one, Rothwell said.

And that’s just the nature of battling diseases, she said. “It’s like an arms race between us and the bacteria. It gets ahead and grows resistant. We get ahead. It just keeps going.”

And for apple growers such as Don Gunderson, this arms race-style battle against fire blight can prove frustrating.

“Last year it affected pretty much every farm in the area,” said Gunderson, the owner of Westview Farm in Mattawan. “People are just scratching their heads.”

Last year he used a streptomycin fungicide, but “it’s only good for so many hours and it rained for three days straight,” he said.

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