What to Do When Mushroom Spawn Becomes Contaminated? A Full Breakdown of Effective Prevention and Control Measures

In the process of mushroom production, spawn making is a key step. During the spawn production process, improper operation, incomplete disinfection and other reasons can lead to the invasion of contaminant fungi, contaminating the spawn, reducing the marketable rate of mushrooms and lowering profits. Below is an introduction to the common contaminant fungi in mushroom production and their prevention and control measures:

1. Penicillium is one of the most common contaminant fungi. After contamination, it appears on the culture medium as small, separate green powdery mold spots. This fungus is extremely widely distributed and spreads by means of airborne conidia attaching to moist materials that have not been thoroughly disinfected. Prevention and control measures: (1) The compost must be strictly disinfected. (2) Strict aseptic technique must be maintained during inoculation. (3) Increase ventilation, lower the temperature and reduce humidity. (4) For localized contamination, wash with 5-10% lime water.

2. Trichoderma is mainly Trichoderma viride or Trichoderma koningii. It spreads by means of spores produced in organic matter such as decaying wood, seeds, plant residues, compost and soil, and spores floating in the air. This fungus prefers acidic conditions, and occurs easily at a temperature of 25-30 degC and a relative air humidity of 80-90%; it can spread from a spot or patch to the entire surface of the substrate within 3-5 days. Trichoderma often grows together with Penicillium, and the two have similar mycelial colors; the difference is that Penicillium changes from white to green or pale yellow, while Trichoderma mycelium is initially white and, after producing green spores, turns green or copper-green and gradually deepens. Trichoderma has strong cellulase activity and can decompose cellulose; it mainly occurs in indoor substrates rich in lignin and fiber, such as sawdust. Because it grows rapidly, in addition to competing with mushrooms for nutrients, it also secretes toxins, so it often forms opposing "island-like" zones and "antagonistic lines" with mushroom mycelium, inhibiting the growth of mushroom mycelium. Prevention and control measures: (1) Strictly disinfect the compost to thoroughly eliminate mycelium and spores in the compost; carry out aseptic operations well and increase ventilation and lower the temperature. (2) When disinfecting, do not use too much formaldehyde, to prevent creating an acidic environment. (3) When Trichoderma appears on the medium, promptly apply 755 alcohol, 15% bleaching powder solution, or 50% carbendazim 200-fold solution locally, spray 1-5% lime water or scatter white lime powder, then dig it out, and afterward smear with lime water. When handling, it is best to move the spawn bags (bottles) outdoors to prevent spores from dispersing. After Trichoderma appears, it is strictly forbidden to open the bottle caps or lift the film at will, to avoid spread. When using plastic bags for spawn production, they should not be moved too much during the incubation period. (4) Promptly remove spawn blocks that have not germinated. (5) The cotton plugs of spawn bottles and spawn bags must not become damp; keep the culture room dry and clean. (6) The mother culture must be pure. (7) When mixing the substrate, add 2 g of 25% (or 5%) carbendazim or 1 g of 75% thiophanate-methyl per kilogram of dry material.

3. Mucor, Rhizopus and Aspergillus. Mucor, also known as long-hair fungus, mainly occurs on the early-stage medium and on spawn of indoor-cultivated mushrooms (wood ear fungi). The mycelium is initially white or grayish-white, then turns pale yellow. The mycelium is sparse and thick, with each strand clearly visible. The higher the water content of the compost, the more severe the occurrence. It has a strong ability to decompose starch and grows very quickly.

It grows in a crisscross pattern on the surface of the substrate, forming loose, needle-like long hairs; after about 3 days, it can cover the entire substrate surface, blocking oxygen, competing for nutrients and water, and secreting toxins, thus affecting the growth of mushroom mycelium. After about 40 hours, it can produce a large number of black spores. Rhizopus is similar to Mucor, except that it has no obvious mycelium in the compost and merely grows prostrate on the surface of the substrate, with no aerial mycelium. Aspergillus occurs easily when the water content of the compost is relatively low and the temperature is high. The mycelium is initially white and cottony, then turns yellow; when the temperature reaches above 27 degC, it produces a large number of spores, which vary in color depending on the species, including black, yellow-green, orange-yellow and orange-red, and spread extremely quickly. Mucor, Rhizopus and Aspergillus are very widely distributed, and their spores are present in soil, fertilizer and air. Prevention and control measures: (1) Thoroughly disinfect and sterilize, and carry out aseptic operations well. (2) When mixing the substrate, add 2 g of 25% (or 5%) carbendazim or 1 g of 75% thiophanate-methyl per kilogram of dry material.

4. Neurospora, also called red bread mold, can cause damage at all levels of spawn production. It occurs especially easily when the temperature is high and humidity is high. This fungus is very widely distributed in nature, and various organic materials, such as corn cobs, corn stalks, cottonseed hulls and waste cotton, are all prone to it. Its conidia float everywhere. When they settle onto the surface of organic matter, they quickly germinate into mycelium. The mycelium spreads very quickly, initially grayish-white or yellowish-white, slender, growing rapidly downward and also growing onto the cotton plug. Outside the cotton plug, it forms a large number of pale red powdery conidia, piled up in masses about 1 cm thick, hence it is also called red powder fungus. With slight vibration, the spores disperse into the air and spread everywhere. Prevention and control measures: (1) Maintain good environmental hygiene, and bury waste compost deeply. (2) Thoroughly sterilize the compost; the cotton plug must not become damp, and if it does, replace it promptly. Spawn bottles (bags) must not be damaged. (3) The inoculation room must be thoroughly disinfected, and aseptic operating procedures must be strictly followed. (4) Scatter lime on the floor, and if necessary also scatter lime on the cotton plugs at the bottle mouths, to keep them dry. Once it is found, remove and burn it promptly, and spray with 75% wettable thiophanate 500-fold solution, or fumigate with 10 mL of formaldehyde per cubic meter of space.