Updated quarantine order expands treatment and reporting requirements to better protect growers and neighbors from nuisance Phorid Flies.
The Pennsylvania Department of Agriculture has made $1 million available in grants through Chester County Conservation District to help farmers fulfill quarantine requirements.
Harrisburg, PA – Today, Agriculture Secretary Russell Redding announced an updated quarantine order, expanding proactive efforts to control Phorid flies, or Megaselia halterata, a destructive pest causing crop losses on Southeast Pennsylvania mushroom farms and creating a nuisance for nearby homeowners. The Shapiro Administration has made $1 million in state funds available through the Chester County Conservation District to support farmers in meeting new quarantine order requirements to control the pests.
Phorid flies do not harm humans and are not a public health threat. The flies and required treatments to control them do not affect the quality of mushrooms in the marketplace.
The Pennsylvania Department of Agriculture (PDA) revised its January 2025 quarantine, broadening the requirements to apply to more farmers and better protect the region’s most valuable crop. The revision is based on industry feedback and crop monitoring since January 2025.
"The department worked with mushroom industry leaders and Penn State researchers to develop safe, effective ways to control this pest, and demonstrated their effectiveness over the past year," Secretary Redding said. “We know these methods are safe and effective, but they only work when every grower is following the best management practices every day. By giving mushroom farmers tools to control pests and financial support to help them do it, the Shapiro Administration is showing that we are committed to helping farmers protect their valuable crops so they can continue to produce top quality products to feed Pennsylvania’s economy.”
The revised order, effective March 23, 2026, requires all mushroom growers in Chester County to steam-treat mushroom houses between crops, as well as the medium used to grow prior crops. Steam treatment, or pasteurization, kills adult flies, larvae, bacteria, fungus, and pathogens, preventing spread to adjacent farms or subsequent mushroom crops. The method is an industry-proven, effective practice for managing the spread of the pest.
Growers must keep records of treatments and the number of insects present. They must also implement one of five additional treatments proven effective in controlling the pests:
- Exclusion and Inclusion Method – sealing entry points and eliminating attractants
- Parasitic Nematodes
- Predatory Mites
- Adulticides – insecticides that kill adult flies
- Long Lasting Insecticide Nets
Phorid flies feed on fungi and reproduce in dark, humid environments, making mushroom houses and the substrate used to grow mushrooms the ideal environment for them to grow and reproduce. Warming temperatures and increased year-round humidity have increased fly infestations. The pest has been shown to reduce mushroom crop yields by up to 40%, and pests that escape mushroom houses have created a nuisance for surrounding residents.
“I am very grateful for the expanded quarantine order and Best Management Practices,” State Representative Christina Sappey said. “The increased resources the department is deploying to combat the phorid fly issue in our county demonstrate the high level of commitment necessary to support not only our residents, but our mushroom growers challenged by lower yields who are in need of resources to employ best practices. I’m also pleased with the accountability measures included in the order. I believe this action and the continued research being done by Penn State will deliver positive results for our southern Chester County communities.”
“Penn State brings some of the top specialists — not just in the nation, but in the world — to the conversation”, said State Representative John Lawrence. “As it relates to specialty agriculture in general and mushrooms in particular, they are putting significant resources and research into this. PDA and Penn State are leading together with an all-hands-on-deck response to a major quality of life issue and a very difficult issue to resolve.”
PDA has funded $627,765 in research to develop safe, effective control methods for Phorid Flies. The department continues to work with the U.S. Department of Agriculture and Penn State University, as well as other industry experts, to support research to develop safe, effective pest control methods that do not use chemicals that may harm the environment and jeopardize food safety and human and animal health.
Pennsylvania leads the nation in Agaricus mushroom sales and production. The center of the state’s mushroom industry is Chester County, where approximately 2,000 mushroom houses are located. According to Penn State University, Pennsylvania produced 69% of mushrooms sold in the U.S. in the 2024-25 growing season. The value of the Agaricus crop was estimated at $1 billion.
In conjunction with experts from Penn State Extension, the department will hold educational sessions for growers in English and Spanish.
“Researchers and extension professionals in the College and Agricultural Sciences at Penn State are working closely with growers on research to determine the best combinations of techniques, called integrated pest management, to reduce fly numbers,” said Troy Ott, Peter and Ann Tombros dean of the college. “Growers need science-based guidance to ensure that techniques implemented will be effective. Our extension professionals are working to ensure that the most up-to-date guidance on phorid fly controls is available to producers in both English and Spanish. We are so grateful for the support of PDA and the Pennsylvania legislature for funding our work through the Land Script line in the state budget.”
Mushroom farmers seeking financial assistance with implementing quarantine requirements may contact the Chester County Conservation District at 610-455-1381 to apply for grant funding.
Learn more about the department’s work to protect Pennsylvania’s plant and animal agriculture industries at agriculture.pa.gov.
Find the revised Quarantine Order and procedures mushroom growers affected by the order should follow, as well as an FAQ for Mushroom Producers and FAQ for Homeowners at agriculture.pa.gov.
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