Penn State Leads Fight Against Phorid Flies in Mushrooms

By Blake Jackson

Phorid flies are significantly impacting southeastern Pennsylvania's mushroom industry, where 60% of U.S. mushrooms are grown, causing up to 40% crop loss and invading homes.

Penn State researchers and Penn State Extension specialists are collaborating with state officials and industry leaders to develop science-based integrated pest management (IPM) solutions.

The Pennsylvania Department of Agriculture has issued a quarantine order and provided $500,000 in grant funding to aid affected farmers.

Agriculture Secretary Russell Redding announced mandatory steam treatment between crop cycles for mushroom farms in Kennett and New Garden Townships, Chester County, following Penn State research-developed best practices. This process raises growing house temperatures to eliminate phorid flies and larvae.

Michael Wolfin, assistant research professor of entomology at Penn State, notes that phorid flies have been a problem since the 1940s. While diazinon was previously used, the EPA banned it in 2012 due to toxicity.

“Since then, Pennsylvania has seen year-to-year exponential growth of the flies in the Kennett Square area of Chester and Berks counties,” Wolfin said. “Kennett Square is unique more than half of the mushrooms in the country are grown in this 250-square-mile area in which there are hundreds of mushroom farms in close proximity, so the flies always have a constant food source.”

The flies are attracted to growing mycelia, the fungal root-like structures in mushroom compost, their sole food source. They mate outside and return to lay eggs in the compost.

“It’s impossible to estimate the number of flies in the area during the peak phorid fly breeding seasons,” Wolfin said. “Although they are not known to harm humans, they create a major nuisance, pouring into the vents of homes in places like Kennett Township, Kennett Square Borough, New Garden Township and Avondale.”

Funded by the Pennsylvania Department of Agriculture and the USDA, Penn State's team is developing an IPM plan with multiple control methods. They are preparing to roll out four strategies alongside steam treatment, which eliminates bacteria and fungi.

These strategies include:

• Adding entomopathogenic nematodes to compost to kill larvae.
• Introducing predatory mites to compost to kill larvae.
• Using registered pesticides as a compost drench or spray to kill adults.
• Hanging insecticide-impregnated mosquito netting to control adults.

“We think our research will bring relief soon,” Wolfin said.

Photo Credit: istock-guruxoox