Post-Crop Steam-Off Tips for Healthy Mushrooms

By Blake Jackson

Steam-off, also called post-crop pasteurization, is a crucial step for controlling pests and maintaining healthy mushroom production. The Best Management Practices for Mushroom Farming manual emphasizes thorough post-crop steaming once harvesting is complete.

After the last flush of mushrooms has been picked, the growing room should be closed off and the room should be pasteurized with steam or steam with added sanitizing agents.

The purpose of steam-off is to reduce the risk of contaminating future crops. Substrate left in the house after harvest can harbor pests and pathogens. Steaming the substrate kills adult flies, their eggs, and larvae, while a second steaming of the empty growing room ensures that the environment itself is sanitized.

Without this process, adult pests can infest new crops and serve as a continuous source for future generations, affecting not only the farm but nearby areas as well. Post-crop steaming also interrupts disease cycles by destroying fungal, bacterial, and viral pathogens present in the substrate or penetrating the wooden beds.

For farms dealing with Trichoderma, nematodes, Mummy, LaFrance virus-infected mycelium, or other pests, steaming both before and after removing substrate is critical. Some pathogens can survive in wood if steamed with substrate still in place.

Steaming empty rooms allows the wood to reach the temperatures needed to eliminate pathogens, which can take five to six times longer than heating the substrate. Beds should be cleaned, moistened, and arranged before steaming to maximize effectiveness.

Recommended temperatures are at least 150°F (66°C) for a minimum of 12 hours when substrate is present, and at least 150°F (66°C) for 24 hours when steaming an empty room.

Research shows substrate alone takes roughly 14 hours to reach 140°F (60°C). Many farms initially raise air temperature high, then lower it once substrate and wood reach target temperatures.

Implementing these post-crop steaming procedures kills insects and pests, reduces contamination risks, and breaks pest breeding cycles, ensuring healthier mushroom production and improved overall crop quality.

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