Control Methods for Rust Spot Disease in Oyster Mushrooms

The rust-colored or dark brown spots appearing on the caps and stipes of oyster mushrooms are called rust spot disease of oyster mushrooms. This disease is a bacterial disease that easily occurs during the fruiting body growth stage of oyster mushrooms. The pathogen causing this disease is a species of Pseudomonas bacteria that is extremely widely distributed in nature. In the early stage of the disease, the spots are only the size of a needle tip and light in color, generally not affecting commercial value. As the disease worsens, the spots rapidly enlarge and their color continuously deepens, often appearing oval or spindle-shaped, or connecting with each other to form irregular large patches, with rust-yellow discolored areas around the patches. When the mushroom bed is severely infected with this disease, the fruiting bodies turn scorched yellow, causing light-colored mushrooms to become yellow mushrooms and dark-colored mushrooms to turn sauce-colored mushrooms. When rust spot disease causes mild damage, although it affects the growth and development of the fruiting bodies, it does not pose a threat. After the damage worsens, it will not only cause the death of the fruiting bodies, but also affect the normal growth of the next flush of mushrooms, and can cause cross-infection with other diseases and pests. Fruiting bodies damaged by rust spot disease become dry and shrunken, with poor color and low commercial value. Severely affected diseased mushrooms have distorted gills, with spore powder that has not been fully released often trapped within the gills, and the caps will also become wrinkled and cracked due to the gradual sinking of the spots, losing commercial value. When oyster mushroom rust spot disease occurs under conditions of high temperature, poor ventilation, excessive watering, and relative air humidity exceeding 95%, the disease spreads quickly and the damage is also severe.

Preventive measures: If rust spot disease occurs, ventilation should be strengthened and relative humidity reduced. For chemical control, a 5% lime clear liquid, a 1:600 bleach solution, a 500-800 times ansuo fungicide aqueous solution, a solution containing 120 units per milliliter of oxytetracycline, streptomycin, gentamicin, or chloramphenicol, or a mixture of 3 parts bleach and 1 part soda ash prepared into a 0.5% mixed solution can be used for spraying. If the oyster mushrooms have already died from the damage, or the mushroom bed is severely infected, then all fruiting bodies on the mushroom bed should be promptly removed, the yellowed, aged, and infected surface mycelium scraped off, the bed surface cleaned thoroughly, and after slight air-drying, a thin layer of lime powder or a small amount of bleach should be sprinkled onto the mushroom bed to reduce the pathogen base on the mushroom bed and prevent the recurrence of rust spot disease after the next flush.