Current Major Diseases of Northern Oyster Mushrooms and Their Control Techniques
1 Soft Rot Disease
1.1 Disease Symptoms The surface of the substrate or the mushroom bodies become covered with a layer of white cottony mycelial threads, fine and soft but growing very rapidly; the gradually infected mushroom bodies develop a light brown morbid condition spreading upward from the base of the stipe, and the mushroom bodies gradually soften and rot; about one week after infection, the mushroom bodies collapse on their own, or topple at the slightest touch, just like Chinese cabbage suffering from soft rot, but the soft-rotted mushroom bodies have no foul odor; mushroom bodies not yet soft-rotted grow extremely slowly, the caps gradually turn earthy yellow, lifeless and dull, clearly different from normal mushroom bodies; infected substrate no longer produces mushrooms, and even if primordia barely form, they quickly soften and rot, having no commercial value.
1.2 Causes of Onset The soft rot pathogen generally survives in the surface cultivation layer (20cm) of the soil, especially in plots with high organic matter content and fertile soil where the pathogen population is very high, such as vegetable garden soil, seedbed soil, and the cultivation layer of land within about 100m around villages. Generally, oyster mushroom production sites are mostly at village entrances and alley corners, in front of and behind houses, and the soil used for cultivation is also obtained locally, making it very easy for the pathogen to contaminate the cultivation substrate. When the temperature inside the cultivation shed is 15-30°C and the relative air humidity is about 90%, the pathogen spores germinate rapidly, and their mycelium first infects the culture substrate. Thereafter, as their numbers expand, the degree of damage gradually deepens, either causing the substrate to no longer produce mushrooms or causing the already-formed mushroom bodies to gradually soften and rot.
1.3 Preventive Measures ① Build cultivation sheds far away from disease-affected areas; this is the fundamental preventive measure. ② When continuing production in disease-affected areas, the cultivation shed should be treated as follows: a. Burning: Remove all the upper frame poles and coverings of the original shed, scrape off 1-3cm from the walls, loosen the ground to about 10cm deep, then spread waste crop straw or firewood about 20cm thick inside the shed, piling more and higher along the base of the surrounding walls, and ignite to burn. Plow the ashes after burning into the soil and level the ground, re-cover with plastic film and seal as tightly as possible; it can be put into use after about 10d. b. Chemical sterilization: Scrape off 1cm from the shed walls, loosen the ground to 5cm deep, then prepare a 6% formaldehyde aqueous solution, using 200-600g per square meter depending on the severity of the disease, and apply blanket spraying for sterilization. Key points to note: First, spray evenly without leaving any dead corners or untreated areas; second, spray quickly, preferably with a high-pressure sprayer operated by 2-3 people; third, immediately seal the shed entrances and ventilation openings after spraying; it can be put into use after one week. Alternatively, depending on the severity of the disease, dissolve 0.3-0.6kg of carbendazim and 0.2-0.4kg of formaldehyde together in 100kg of water, treat the shed as described above and spray evenly; this also has a very good effect. ③ Add carbendazim at 0.3% of the dry material weight to the cultivation substrate or use an active fermentation agent for high-temperature heap fermentation (65-70°C) treatment. ④ Treatment of cultivation soil: Collect soil from areas far from the cultivation zone, from old cultivation areas, or from original spawn-running areas; sieve so that soil particles are below 3mm in diameter; sun-dry the sieved fine soil, preferably making it thoroughly dry; for each ton of soil, use 250g of 50% carbendazim and 400g of 36% formaldehyde mixed with 500kg of water, spraying while mixing, mix twice and use up all the solution, then cover with plastic film; after about one week it can be taken and used as needed. ⑤ After mushroom bags have been in the shed for some time, especially after fruiting begins, if white cottony (fuzzy) mycelium appears on the surface of the substrate, immediately use a knife or shovel-like tool to scrape off about 2cm of the substrate in the affected area, apply 400-fold carbendazim solution to that area, remove the scraped material cleanly and burn it; do not use burial, and certainly do not discard it carelessly. ⑥ Once infected mushrooms appear, immediately increase ventilation and stop watering, reduce the air humidity in the shed to the minimum, immediately remove the diseased mushrooms, clean the affected area and handle the diseased mushrooms according to the above measures, and soak the tools used in 400-fold carbendazim solution for sterilization. After 1-2 weeks, if no mold mycelium has grown, normal management can be resumed. ⑦ In the early stage of the disease or when no mushrooms are growing between flushes, a comprehensive scraping treatment can be carried out on the surface of the substrate, using the same method as above. ⑧ For cultivation sheds with severe disease or where the disease was discovered late and has already caused serious damage, the above treatments need not be carried out; only clear out the substrate, re-sterilize the shed, and then carry out cultivation production again.
2 Rot Disease
2.1 Disease Symptoms In the early stage, light yellow water-soaked spots and patches appear on the caps, which then quickly cause the mushroom bodies to become light yellow or earthy yellow water-soaked, rot, and give off a foul odor; severely affected sheds smell as bad as chicken coops, and the infected mushroom bodies rot as if cooked, losing their edible value.
2.2 Causes of Onset Bacteria are extremely small and widely present in substrate, water, and soil; airborne transmission, introduction by humans, and introduction by pests are all important causes of onset. Bacterial diseases are especially likely to occur when the substrate fermentation is incomplete or uneven, or when the spawn-running or fruiting sites are not clean. Because bacteria spread very rapidly under suitable conditions such as 10-30°C and 90% relative air humidity, the damage is very great. When the temperature is too high or too low and the humidity is too low, bacteria can form dormant spores, which can persist for long periods under unfavorable environmental conditions and germinate when conditions become suitable, continuing to cause damage. In addition, high-temperature environments, especially during winter and spring cultivation when sheds are kept warm, are generally accompanied by poor ventilation, which is also an important reason why bacterial diseases can cause regional damage.
2.3 Control Measures ① Substrate fermentation must be thorough and uniform, and 0.2% formaldehyde should be added before sowing, mixed thoroughly before bagging and sowing. ② Before use, culture and mushroom shed sites should first be sprayed with carbendazim-formaldehyde solution for sterilization. ③ Spray 600-fold DDV insecticide around the mushroom shed to prevent introduction by pests. ④ When water-soaked spots are found on mushroom bodies, promptly inspect the disease situation in the shed; if infected mushrooms exceed 20%, immediately remove all diseased mushrooms, scrape off 1-2cm of the surface layer of the infected area, clear it out of the shed and burn or scald with hot water; alternatively, spray with 5% formaldehyde and then deep-bury. ⑤ For severely affected sheds, immediately increase ventilation, stop watering, remove diseased mushrooms and healthy mushrooms to create a mushroom-free period, and spray once each with 6% formaldehyde solution and 200 units of streptomycin or 1% bleaching powder.
3 Truffle Disease
3.1 Disease Symptoms The mycelium of this fungus resembles oyster mushroom mycelium and cannot be distinguished with the naked eye. It can penetrate deep into the substrate to compete with oyster mushroom mycelium for nutrients, water, and living space, inhibiting oyster mushroom growth and causing it to lose fruiting capacity. After its mycelium reaches physiological maturity, it forms ascocarps on the fruiting surface of the substrate, especially in bed cultivation where it occurs over large areas in the region where the mushroom column contacts the soil; the gregarious or clustered ascocarps have a brain-like wrinkled block shape, closely resembling walnut kernels with the astringent skin removed, wrinkled and unpleasant-looking; when they first appear, most mushroom farmers mistake them for oyster mushroom primordia, but after several days there is still no differentiation; only the initial milky white of the ascocarps turns light milky yellow, then gradually light yellow-brown to brown-red, and their volume keeps expanding; by the time various control measures are hastily taken, it is already too late. When this disease occurs severely, it can cause an entire batch of substrate to produce no mushrooms at all. A high concentration of bleaching powder odor in the shed is one of the important indicators of truffle disease occurrence.
3.2 Causes of Onset Diehliomyces microsporus is a malignant contaminant fungus in edible mushroom cultivation production. Its spores exist in large quantities in soil or substrate and have extremely strong vitality; at 16-35°C and air humidity above 70%, they can germinate quickly and cause damage. This pathogen is especially harmful to oyster mushrooms cultivated with casing soil.
3.3 Control Measures ① The substrate must undergo thorough and uniform heap fermentation treatment, and the moisture content must not exceed 63%. ② Treatment of cultivation soil refers to the above. ③ Before mushroom bags enter the shed, in addition to treating the shed as required above, re-spray 1-2 times with bleaching powder solution at a concentration of 1.2% or above at 5d intervals. In areas with a disease record, also add one spraying of carbendazim and formaldehyde solution. ④ Once truffle disease is found, immediately increase ventilation in the shed, reduce temperature and humidity, and dig out the affected area and its outer edge of 3cm (depth depending on the time and severity of onset) together with soil and substrate, backfill with treated fine soil, and spray the entire shed with 1% bleaching powder solution in a blanket manner once, and apply 400-fold carbendazim solution to the dug-out affected areas.
4 Downy Mildew Disease
4.1 Disease Symptoms In the early stage, white cottony mycelium forms on the surface layer of the substrate and slowly expands its coverage; wherever its mycelium reaches, no mushrooms are produced; it then infects normal mushroom primordia and the base of mushroom bodies, causing the mushroom bodies to turn light earthy yellow to yellow-brown, soften, and rot; the rotted mushroom bodies have a slight odor in the later stage, but much less odor than rot-diseased mushrooms infected by bacterial diseases. The infected mushroom area and the area covered by mold mycelium no longer produce mushrooms.
4.2 Causes of Onset This mold can occur and cause damage within the temperature range for oyster mushroom growth, and mostly occurs in the cultivation season from late autumn to early spring, showing a trend of low-temperature onset. Especially since this season is also the golden period for large-scale substrate preparation, the severity of this disease is felt even more. The mold spores parasitize in large quantities in soil, substrate, and water, and can also be transmitted through air, humans, and insects; the spores ejected by infected mushroom bodies are one of the important pathways for worsening the damage.
4.3 Control Measures ① For treatment of cultivation sheds and cultivation soil, refer to "Soft Rot Disease Control." ② After diseased mushrooms are found, immediately increase ventilation in the shed, stop watering to dry the substrate surface, promptly remove diseased mushrooms and burn them; never discard them carelessly and create new sources of contamination. ③ Treat used tools and disease-affected areas with 5% formaldehyde or 80-fold bleaching powder. ④ For severely affected sheds, after all mushrooms are harvested, treat the substrate surface accordingly, scrape off the surface layer, re-spray carbendazim and formaldehyde solution and seal for 48h, then increase ventilation, do not water, and after about 10d resume fruiting management. ⑤ Once this disease is found in specialized edible mushroom production villages (districts), visiting each other's sheds and tours should be prohibited to avoid cross-contamination.
5 Stiff Mushroom Disease
5.1 Disease Symptoms Young mushrooms are infected before differentiation, dying while very small, with cap diameter of about 1cm; the entire mushroom body (mushroom cluster) appears dry, white, and stiff, not soft, not rotting, not smelly; some caps have tightly stretched, shiny surfaces, and some caps appear to have a powdery layer. No abnormal changes are seen in the substrate, but no further mushrooms will be produced thereafter.
5.2 Causes of Onset This mold parasitizes in large quantities in the crevices of soil and mushroom sheds and in raw materials; air, humans, and insects are also important transmission pathways.
5.3 Control Measures There is no specific effective control drug; the focus is on "prevention," appropriately lowering the temperature inside the shed and increasing ventilation; for chemical control, refer to "Soft Rot Disease."