Causes of and Preventive Measures against Contaminant Infection in Northern Nameko Mushroom Cultivation

As the production volume of northern nameko mushrooms increases year by year, diseases have become severe, causing reduced yields in mild cases and total crop failure in severe cases. In fact, diseases of edible fungi are not incurable; as long as we understand their occurrence and development patterns and find effective control methods, the problem can be solved. Through years of cultivation practice, the author has identified the patterns of contaminant infection. The causes and preventive methods are presented below:

1. Late inoculation - starting inoculation only in April is too late, as the weather has already turned warm and is prone to contaminant infection. Inoculating in February-March is best, because edible fungus mycelium begins to germinate and grow at above 5°C, while molds only proliferate in large numbers above 15°C. Therefore, early inoculation should be arranged with low-temperature mycelium incubation to pass through the mold infection stage.

2. Pine sawdust mixed into the substrate - pine sawdust contains bactericidal substances that can inhibit the growth of nameko mycelium; the mycelium will not colonize the substrate, leading to massive contaminant growth in the later stage and failure.

3. Aged spawn - the most suitable spawn age is about 40-50 days from the start of inoculation. Aged spawn has mature mycelium that grows slowly and is prone to contaminant infection in the later stage. Spawn produced early should be stored below 4°C to keep the mycelium dormant, which can prevent aging.

4. Not strictly enforcing sterile technique indoors - rural nameko cultivation has no dedicated inoculation room, and inoculation is mostly done in residences, with many opportunities for contamination. Therefore, sterile technique must be strictly enforced. For example, the inoculation room and mushroom house must be thoroughly disinfected; walls and greenhouses must be whitewashed (brushed once with white lime); all tools and plastic films must be soaked in 3% Lysol. Workers should wear disinfected white lab coats, hats (covering hair), and masks, first wash their hands thoroughly, then wipe hands with 75% alcohol cotton balls before operating. During inoculation, no other people should enter or leave, and smoking, spitting, or talking should be avoided. After racking, spray 3% Bordeaux mixture indoors at regular intervals.

5. Insufficient inoculation amount - normally the ratio of substrate to spawn is 10:1. If the inoculation amount is insufficient, mycelium grows slowly and is prone to contaminant infection. Appropriately increasing the spawn amount, such as 10:1.5 or 10:2, results in very little contaminant infection.

6. Steaming and inoculation not synchronized - some mushroom growers first steam the substrate in bulk, then inoculate in bulk several days later, which increases contamination opportunities. The correct approach is: while the substrate is hot, bag or package it, cool it indoors, and inoculate the same day; do not delay to the next day.

7. Hidden dangers in old mushroom houses - old mushroom houses have many contaminant spores and are highly prone to contaminant infection. Therefore, before cultivation, disinfect and whitewash once again, using two disinfectants alternately.

8. Imbalance in the ratio of bran (wheat bran) to sawdust - when mixing, bran and wheat bran should not exceed 20%, otherwise poor aeration leads to souring and contaminant infection. In addition, bran and wheat bran must be fresh; sour or moldy ones cannot be used.

9. Environmental pollution - if the surrounding environment is unclean, there are many contaminant spores, causing severe infection. The cultivation site should be chosen in a place with fresh air and good ventilation; there should not be manure piles, poultry and livestock sheds, or garbage heaps nearby.

10. Mycelium blocks too thick - the suitable substrate thickness is 8 cm, that is, filling 10 cm of substrate and compressing it to 8 cm. If the mycelium block is thick, the time for mycelium to fully colonize the substrate is prolonged, and the contaminant infection rate is high.

11. Using old plastic film - old film that has been used once, especially old film contaminated by mold, has a high infection rate. If old film is used, first rinse it with alkaline water, then soak it in 3% Lysol solution for a full day and night, take it out, shake off the water droplets, and then use it.

12. High humidity in the mushroom house - during mycelium growth, indoor relative humidity should not exceed 70%, that is, it is better to be dry than wet. During fruiting, however, high humidity is needed; if humidity is high, ventilation can be increased, and quicklime can be placed indoors to absorb moisture.

13. Excessive moisture in mycelium blocks - the moisture content of nameko substrate should not exceed 65%; excessive moisture slows mycelium growth. If the mycelium has already penetrated 1 cm but stops growing due to excessive moisture at the bottom (high substrate moisture content with much water), the mycelium block can be turned over, and the mycelium will continue to grow.

14. Direct sunlight on mycelium blocks - when mycelium blocks are racked for mycelium cultivation, they must be kept away from light; scattered light indoors is sufficient. If direct sunlight hits the mycelium blocks, mycelium growth will be inhibited. Therefore, cultivation should be done away from light, and sunlight must not fall on the mycelium blocks.

15. Dead corners in ventilation - mycelium growth requires oxygen. Good ventilation during the mycelium incubation period allows mycelium to grow rapidly and colonize the substrate ahead of time. Therefore, when building a mushroom house, north and south windows should be equal in number, windows should be large, ground-level windows should be built flush with the ground, and a ventilation chimney should be installed on the roof.