Strong demand for organic mushrooms in the U.S. provides an economic opportunity for growers, but sciarid and phorid fly pests, fungal and bacterial diseases, and the lack of National Organic Program (NOP)-allowed growing media and pest and disease control materials constrain the growth of the organic mushroom industry. This project evaluated cultural practices and NOP-allowed materials to manage these challenges in production of organic Agaricus button mushrooms.

Common diseases include dry bubble (caused by the fungus Lecanicillium fungicola), bacterial blotch (Pseudomonas spp.), and a newly emerging (since 2011) fungal pathogen, Syzygites megalocarpus. Sanitation measures, including avoiding mushroom cap wetness and prompt removal of dead or diseased mushrooms from production areas after harvest slow the spread of diseases. Incidence of blotch appears to be related to the balance of the Agaricus microbiome, including pathogenic Pseudomonas spp., disease-suppressive bacteria, and bacteriophage (viruses) that attack blotch pathogens. Additional research is underway to develop practical biological control for blotch.

Phorid flies do much of their damage by facilitating the spread of fungal pathogens. Wettable dust (WD) and contact aerosol (CA) formulations of the NOP-allowed pesticide EcoVia (active ingredients thyme oil and the natural ester phenethyl propionate) proved effective against phorid and sciarid flies. An attract-and-kill strategy was developed utilizing the fly’s attraction to light and EcoVia WD. These methods reduced fly populations 50-99% and improved organic mushroom yields by up to 25%.