Shapiro Administration Takes Action to Support Southeast PA Mushroom Farmers in Controlling Destructive Pest Phorid Fly

Agriculture Secretary Russell Redding announced that the PA Department of Agriculture has taken a new, proactive step, in issuing a quarantine order to control Phorid Flies, or Megaselia halterata, a destructive pest causing crop damage to mushroom farms in Southeast Pennsylvania and creating a nuisance for nearby homeowners. It does not harm humans or present a public health threat.

The department has also made $500,000 in funding available through the Chester County Conservation District to farmers subject to the quarantine to help implement required treatment on their farms.

The order requires all mushroom growers in Kennett Township and New Garden Township in Chester County to steam-treat mushroom houses and previously used growing medium between 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.

"We have been working closely with the mushroom industry and Penn State researchers for many years, seeking safe and effective solutions to this persistent pest plaguing one of Pennsylvania’s most valuable crops," Secretary Redding said. “Steam treatment has proven to be safe and effective, but the method only works if 100% of growers use it. The Shapiro Administration is committed to working toward safely managing these pests for the good of all mushroom growers, and for the neighbors who share frustration with the pests. With this step, we are offering both a proven control method, and financial assistance to farmers to help implement the practice."

With 465.8 million pounds worth nearly $531 million produced in 2023, 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.

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 contributed to population increases. 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.

The mushroom industry has multiple insecticides, fungicides, and herbicides labeled and approved for use controlling Phorid Flies. Steam-treatment is a critical element of the control methods accepted by the industry as a best management practice.

American Mushroom Institute President Rachel Roberts concurs that many in the industry need support and resources to meet their commitments to being good neighbors, stating. “AMI members continue to test and develop strategies to combat Phorids and they stand ready to adopt new tools and practices based on the research conducted with the industry. We welcome this significant investment from the Department of Agriculture to assist farmers and the community.”

The quarantine order, effective January 30, 2025, requires growers to steam-treat between crops as prescribed in step-by-step instructions accompanying the order. Growers are required to keep records of treatments and submit reports to the department. Farms are subject to periodic inspections.

In conjunction with experts from The American Mushroom Institute and Penn State Extension, the department will hold educational sessions for growers in English and Spanish.

Mushroom farmers seeking financial assistance with implementing the requirements may contact the Chester County Conservation District at 610-455-1381 to apply for grant funding.

The Pennsylvania Department of Agriculture has funded nearly $445,000 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.

Learn more about the department’s work to protect Pennsylvania’s plant and animal agriculture industries at agriculture.pa.gov.

Find the 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.