Andrey Repin
Composting specialist, consultant.
Trichoderma is the most common competitive fungal organism when growing white and brown button mushrooms. There are several Trichoderma strains: Trichoderma harzianum, Trichoderma viride, and Trichoderma koningii. The most dangerous and aggressive strain is Trichoderma harzianum. All strains are very common in nature.
For a more precise understanding – Trichoderma spores are everywhere: at home, on clothes, on the street, on all surfaces. Therefore, sooner or later, any mushroom production encounters the green mold problem. The appearance of any strain is a dangerous signal, and actions must be taken immediately and as decisively as possible because the presence of green mold indicates a production problem. Even if this batch has a non-aggressive Trichoderma, the next batch might not be so lucky, and Trichoderma harzianum could appear, which will lead to significant damage.
There is an ongoing dispute between compost producers and mushroom farms about the origin of green mold. I believe that if it appears, everything must be carefully checked both in compost and mushroom production. Only joint actions will bring good results. We will examine the possible causes of green mold in compost production. There are no fewer reasons on mushroom production.
Considering the widespread distribution of Trichoderma in the environment and the very similar conditions for Trichoderma and mushroom mycelium growth, the line between good and bad is very thin. Compost that has passed all production stages correctly and is suitable for mushroom mycelium growth is called “selective”. If there were problems during production, such compost is called “non-selective” – this means that competitive molds can appear on such compost, and Trichoderma is one of the most likely diseases. I will immediately clarify – we will consider possible causes, and they will not necessarily lead to Trichoderma in 100% of cases, but if they exist, Trichoderma will appear sooner or later. If there is a combination of several factors, then Trichoderma is more likely to appear than not.
Let’s start with raw materials. The quality of straw is important in compost production and green mold prevention. Old bales with rotting straw, or conversely, very fresh straw with a good waxy layer, can cause Trichoderma. In compost with old, rotten straw, it is difficult to maintain structure, which in turn leads to disruption of ventilation and anaerobic conditions in the compost. These are conditions for green mold development. When using fresh straw “straight from the field”, there is a danger that not all easily accessible carbohydrates will be transformed, the wax layer will remain, which will prevent the penetration of manure and moisture into the straw. The compost will be sticky, greasy, and look wetter than it actually is. This can also lead to Trichoderma appearance. Chicken manure should be fresh; the time from unloading from the poultry house to use should not exceed one month. Otherwise, pH will decrease, ash will increase, and Trichoderma grows well at pH below 6.0. Also, the gypsum dosage must be observed. This will help maintain structure and correct pH.
The compost formula is important. Low nitrogen levels and decreased C/N ratio can promote active Trichoderma growth due to the inability to transform all easily accessible carbohydrates, low compost activity, and low ammonia levels, which reduces pasteurization quality.
Straw soaking is an important stage of compost production. This helps remove the waxy layer from the straw and initiates the fermentation stage. If this is not done, easily accessible carbohydrates can cause green mold.
Mixing straw with chicken manure and gypsum is a very important moment in compost production, and many things can go wrong at this stage. There are two types of mixing in compost production – micro and macro mixing. By micro-mixing, we mean that each straw is covered with chicken manure. Good equipment and its proper use help in this matter. By macro-mixing, we mean that throughout the batch from beginning to end, mixing proportions were maintained, and the compost did not become one where, for example, at the beginning of the batch 800 kg of manure per ton of straw was added, and at the end 300 kg. Here the technologist’s work is crucial – how they correctly calculate the straw feeding rate and chicken manure feeding rate. Our goal is to mix as high-quality and evenly as possible from beginning to end.
Special attention should also be paid to straw feeding – the flow should be uniform, without interruptions, and chicken manure – the level in the hopper should be constant, without reduction and breaks. All further reloading can slightly level the compost if errors were made during mixing, but will never make it good. If this happens (uneven mixing), we get compost sections with a large amount of manure and small amounts, possibly just straw without manure. The entire compost will be different in activity, structure, temperature, and even humidity. There will be areas that are better ventilated and areas that are worse ventilated. This can cause Trichoderma. In areas with low nitrogen levels, easily accessible carbohydrates will remain; areas with high nitrogen and a large amount of manure will be worse ventilated – creating anaerobic conditions that will lead to green mold development in the compost.
During turns, it is important to monitor the condition of the bunkers. Nozzles before each loading must be cleaned, and air must pass through them freely. Uniform watering and bunker loading are also important. With clogged nozzles, in over-moistened areas or areas with high loading, anaerobic conditions will arise, which can cause Trichoderma. Another important point is cleaning the area and moving residues and spilled compost. Compost from later batches (fresher compost) cannot be mixed with compost from earlier batches (compost at a later production stage). Fresh straw and manure during the last reloading are unacceptable. This can lead to Trichoderma development.
During Tunnel Loading, the area, equipment, and loader must be clean: there should be no compost residues from previous operations, fresh straw, or chicken manure. All these materials will be not fully or not composted at all, with a large amount of readily available nutrition for green mold. Tunnels must also be ready for loading: nets for pulling out compost must be washed, the tunnel tray must be clean, tubes and channels for condensate removal from air ducts must be rinsed, compost residues at the beginning and end of tunnels must be removed. Temperature and oxygen sensors must be serviceable. Tunnels must be sealed. Fresh air intake must have G9 class filters (these filter classes also trap green mold spores). During loading, the compost flow must be uniform. Loading should be done in several layers, like brickwork. Large differences in tunnel loading levels are not allowed to ensure uniform aeration of the entire tunnel compost. All these details help prevent green mold appearance.
A washed net is better ventilated, preventing anaerobic conditions. Compost residues in the tray and at the beginning and end of the tunnel are not ventilated and can preserve infection even at high temperatures (remember that the temperature at the edges and in the tray is always lower). Condensate water can moisten the compost and create heavy, wet, and non-ventilated areas, which can subsequently be infected with green mold. The oxygen sensor will help prevent anaerobic conditions, and temperature sensors will help maintain maximum control over the tunnel compost condition. Quality filters will prevent re-infection of the compost after pasteurization.
No less important are the processes occurring in the tunnel: leveling, pasteurization, and conditioning. During leveling, we must not only level the temperature in the tunnel but also give time for actinomycetes to recover. This will help them survive pasteurization and recover during conditioning. During pasteurization, it is important to observe the temperature regime – 56-60°C, and pasteurization duration – on average 8 hours. The ammonia level is crucial for quality pasteurization, which helps destroy Trichoderma as well.
During conditioning, it is important to ensure that the compost is completely cleared of ammonia. If residual ammonia remains in the compost, the mycelium will die after spawning, the compost will remain uncolonized, and green mold will likely appear in these areas. After the compost is cleared of ammonia, cool it to 25°C. Compost cannot be seeded hotter than 30°C. High temperature can kill the mycelium and provoke green mold development.
Preparation for spawning is the most critical stage for preventing compost infection with green mold. All equipment, rooms, and tools must be cleaned, washed, and disinfected. Cleaned means no compost residues should remain. The two-straw rule works best. This means there should not be two straws lying next to each other because disinfection will not penetrate between them, and Trichoderma may develop in these places. Washed means all compost residues are rinsed, and the greasy film from compost on equipment and floors must be washed off. Disinfection should be carried out on completely cleaned and washed equipment and premises.
Tunnels before spawning must also be cleaned and washed. After this, tunnels must be steamed. Steaming should be performed at a temperature of 70°C and last 12 hours. It is possible to use tunnels after pasteurization without steaming. This is equivalent to steaming. Also important is mycelium storage and shelf life. If the mycelium storage room temperature fluctuates, the mycelium may begin to grow, or condensation may form when the temperature changes. All problems with mycelium can lead to Trichoderma development in the compost. After disinfection, working supply ventilation with air filtration similar to tunnels is needed. This will maintain clean air in the room by creating positive pressure.
During Compost spawning, the same rules apply to tunnel loading as when loading tunnels for pasteurization. When entering the spawning hall, several rules must be followed. Clothing must be clean, preferably using disposable overalls. A disinfectant mat must lie at the entrance. Before entering, one must step on it with both feet. This method of entering the room must be followed by all entering people. Visits during seeding should be minimized. If repair work is necessary, tools must be washed and disinfected. Following these rules will minimize Trichoderma infection risks.
Spawn addition needs to be highlighted. Its quantity should be sufficient – about 8.5 liters per ton of Phase 2 compost. Low quantity will lead to slower colonization and increases the risk of green mold development in the compost. The flow of compost and spawn must be uniform. If the compost flow decreases, the spawn flow must decrease identically and vice versa. If there are areas in the compost with more mycelium, these areas will have more active colonization, the temperature will be higher than in the surrounding compost, which can lead to mycelium burning and dark compost formation, on which green mold will subsequently develop.
Compost during colonization should remain in the tunnel for 15-17 days. This time is sufficient to fully colonize the compost. A shorter cycle increases green mold risks because the compost may not be fully colonized, leaving room for Trichoderma. Also, with early tunnel unloading, we may encounter the peak of compost activity during colonization, which will create difficulties in temperature control at mushroom production, with compost burning and green mold development.
Compost temperature during colonization is very important. Button mushroom mycelium grows best at 25°C. Trichoderma develops faster at temperatures above 26°C. It should also be considered that at temperatures above 28°C, mushroom mycelium virtually stops growing, while Trichoderma continues to develop well. At temperatures above 30°C, champignon mycelium begins to die. Temperature control in the tunnel is critically important for preventing green mold appearance.
Compost shipment is the final stage at the compost plant. It is important that trucks arrive clean. This is especially important if trucks come from mushroom productions, which always have a high background of diseases. The truck bed and wheels must be treated. Drivers should not move through the loading corridor. Equipment, tools, and premises between reloading must be cleaned, washed, and disinfected.
As can be seen, during compost production, there are many nuances, and it is very easy to make a mistake or miss something. Attention to details and understanding that there are no trifles will help keep compost production under control. And you need to understand that even from compost with production problems, with careful handling, good results can be obtained. Conversely, even from the highest quality compost, with improper use, a mediocre result can be obtained.
Read more Andrey- UMDIS posts:
1)The C/N Ratio in Mushroom Compost.
2)5 Rules for Managing Nitrogen Content in Mushroom Compost
