In southeastern Pennsylvania, where 60% of U.S. mushrooms are grown, phorid flies are posing a threat to the industry, destroying up to 40% of the crop and invading homes. To combat the pest, Penn State researchers and Penn State Extension specialists are working alongside state officials and industry leaders to establish science-based integrated pest management solutions.
The Pennsylvania Department of Agriculture recently issued a quarantine order and allocated $500,000 in grant funding to support affected farmers. As part of these emergency measures, Pennsylvania Department of Agriculture Secretary Russell Redding announced that mushroom farms in Kennett and New Garden Townships in Chester County must implement steam treatment between crop cycles, following best practices developed by researchers at Penn State. This process involves raising the temperature of mushroom growing houses to the point that neither phorid flies nor their larvae can survive.
Phorid flies have been a problem on mushroom farms since the 1940s, and for decades farmers used a pesticide called diazinon to eliminate them from their crops, according to Michael Wolfin, assistant research professor of entomology at Penn State. But in 2012, the Environmental Protection Agency ruled that the pesticide was too toxic and could no longer be used in mushroom production.
"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 tiny insect is attracted to the aroma of the growing mycelia - the root-like structures of fungi - in the mushroom compost, Wolfin explained, adding that the only thing that these mushroom phorid larvae can eat is mycelia. Most of the flies go outside the mushroom houses to mate and then return to lay eggs in the compost to reproduce.
