How to prevent and control miscellaneous bacteria contamination during the mycelial growth stage of oyster mushrooms

Recently many mushroom growers have called to consult: during the mycelial growth process of oyster mushroom bags, severe contamination by miscellaneous bacteria has occurred, especially with green mold and Chondrostereum sp. accounting for the majority. How should this be prevented and controlled? In response to this problem, based on investigation and research in recent years, the following causes and control methods have been summarized:

1. Moisture-damaged and contaminated substrate

Fresh, dry substrate that has been well managed in storage contains relatively fewer pathogens and is suitable for raw-material cultivation, but substrate that has been stored for a long time and has become damp and clumped will contain more pathogens. If it is used directly for raw-material cultivation without disinfection treatment, it is very likely to cause miscellaneous bacteria contamination. If the substrate shows clumping and moisture damage, it should be subjected to fermentation treatment or used for sterilized-substrate cultivation. When carrying out fermented-substrate cultivation and fermentation cultivation, fungicides specifically for edible fungi such as Kemeiling and Junjuesha should be mixed into the substrate, and the amount of quicklime added can be 3%-6%.

2. Contaminated spawn

Oyster mushroom spawn should be used immediately once it is fully colonized by mycelium. Otherwise, prolonged spawn age will form a very thick aged mycelial skin, or low temperatures will cause the spawn bags to produce mushrooms in large quantities. Both of these should be regarded as aged spawn. Using such aged spawn results in slow mycelial germination and low mycelial resistance to contamination, and the miscellaneous bacteria contamination rate will certainly be higher than with young spawn. Therefore, when purchasing spawn, mushroom growers should definitely order and buy age-appropriate spawn from reputable spawn farms to avoid losses.

3. Poor spawn quality

Some mushroom growers only seek a cheap price and disregard spawn quality, purchasing poor-quality spawn. After such spawn germinates, the mycelium is sparse and grayish in color, and after the mycelium grows well the substrate does not easily clump together. This kind of spawn has poor decomposition ability and very weak resistance to miscellaneous bacteria, so after inoculation it is also very susceptible to miscellaneous bacteria contamination.

4. Improper management during mycelial growth

The suitable mycelial growth temperature for oyster mushrooms is between 20-32°C. When the temperature is higher than 35°C, the mycelium stops growing; at this time, attention should be paid to turning the stacks in time, and strictly preventing the stack from overheating. When the temperature is higher than 40°C, the mycelium will soon die, and miscellaneous bacteria such as Coprinus will occur in large numbers.

However, the mycelial growth temperature is not better the lower it is; it must be moderate. If the temperature is lower than 15°C, oyster mushroom mycelium grows very slowly at this time, while miscellaneous bacteria such as green mold have a high chance of occurring. Try to adjust the mycelial growth temperature of the mushroom bags within the suitable range.