How to prevent and control oyster mushroom Dactylium soft rot

This disease is caused by infection by Dactylium dendroides of the Deuteromycotina, also known as tree-like Verticillium wilt, cobweb mold, etc., and is a type of damage that causes soft rot of oyster mushroom fruiting bodies.

(1) Pathogen characteristics and damage symptoms: The pathogen hyphae are white, the aerial hyphae grow vigorously and densely, cottony; conidiophores grow directly from the aerial hyphae, slender and sparse; the conidiophore sterigmata branch in whorls, with tapering tips, on which 1~3 conidia are borne singly or in clusters; the conidia are colorless or pale yellow, long oval or pear-shaped, with a size of 20μm~5μm.

In the early stage of disease on the mushroom bed, a thick layer of white cottony hyphae grows on the surface of the substrate or the casing soil. When temperature and humidity conditions are suitable, they often cover the mushroom bed to form a cottony mycelial mat, which is easily mistaken for oyster mushroom hyphae. When the mushroom bed is severely infected, primordia at the affected sites cannot form or are inhibited, and the pathogen further attacks the growing fruiting bodies; when fruiting bodies become diseased, it starts first from the base of the stipe and gradually spreads upward, showing light brown soft rot symptoms; after severe infection, the stipe and gills are covered with white pathogen hyphae, or the diseased mushrooms together with the mushroom bed area where they grow are surrounded and covered by the pathogen hyphae in a spiderweb-like manner, ultimately causing the entire diseased mushroom to become light brown and soft-rotted; the pathogen hyphae later turn light red, and purple-red pigment is produced at the center of the disease focus. After oyster mushrooms are infected with this disease, the fruiting bodies generally do not become deformed, nor do they emit an off-odor, but the diseased mushrooms collapse when touched by hand; diseased mushrooms with mild infection that have not yet shown soft rot symptoms have their growth and development hindered, appear dirty yellowish-white, lifeless, and are clearly different from normal healthy mushrooms.

(2) Infection pathways and occurrence conditions: The pathogen is a weakly parasitic soil fungus that prefers acidic, moist environments rich in organic matter, and is most abundant in fertile seedling beds, vegetable garden soil, and surface soil. The pathogen can directly invade the mushroom bed along with the substrate or soil, and conidia can spread through airflow, insects, diseased mushrooms, and water splash.

The germination rate of pathogen conidia is highest at 20°C, and 25~30°C is unfavorable for germination; they easily die when exposed to high temperatures (60~70°C). The optimum temperature for pathogen hyphal growth is 25°C, and the optimum pH is 3.4 (growth range 2.2~8.0). Conidial germination and hyphal growth are most suited to saturated humidity. When the oyster mushroom bed is in direct contact with contaminated soil, or when open-field sunken beds, outdoor plastic greenhouses, and solar greenhouses are used as mushroom yards, or when cultivation is carried out in civil air defense structures with moderate temperature and high humidity, this disease is prone to occur.

(3) Control measures

1) Refer to integrated pest and disease management measures for oyster mushroom cultivation.

2) The ground and soil that come into direct contact with the mushroom bed must be disinfected and pretreated before use.

3) During the fruiting stage, the mushroom bed should be managed with alternating wet and dry water management, and a good ventilation and air exchange environment should be maintained. During the interval between flushes, in addition to cleaning the bed surface, 1%~2% clear lime solution should also be sprayed regularly to prevent excessive acidification of the mushroom bed.

4) Once this disease occurs, stop spraying water, immediately ventilate to reduce humidity, remove the diseased mushrooms, and scrape away the pathogen mycelial mat; contaminated casing soil should be removed or replaced. After reducing humidity, the affected areas can be sprayed with 2%~5% formaldehyde solution, or 50% carbendazim 800~1200 times dilution, or 5% clear lime solution, or 150~250mg/kg bleaching powder solution, or the infected areas can be covered with a thin layer of lime powder or bleaching powder.