Causal Organism

Several strains of Trichoderma spp. have been associated with the commercial production of A. bisporus. Some are found as a weed or indicator mold that signals a composting or casing pH problem (Wuest, 1982). In the late 1980s, a new, more pathogenic strain was reported in Ireland and the UK, Trichoderma harzianum (Th2 and Th4).  During the 1990s, it spread to Canada and the United States and eventually has been found worldwide in many mushroom-growing operations, and is now classified as Trichoderma aggressivum f. aggressivum (Ta2). This aggressive strain causes the disease known as Trichoderma Green Mold. This pathogenic strain has been found only on mushroom farms. Trichoderma Green Mold spreads throughout mushroom crops and farms through vegetative growth and the production of conidiospores.

Signs and Symptoms

Trichoderma mycelium grows as a grayish color and then changes to white, becoming very dense. Growth during the spawn growing is difficult to discern from the mushroom mycelium.  Once it begins to form spores, it turns dark green (Figure 1).  Green Mold mycelium grows in the substrate, and the casing aggressively competes with the mushroom mycelium. Often, little to no mushroom mycelium is found in areas heavily colonized with Trichoderma.

Other Trichoderma species will not cause the disease and only through extensive taxonomic examination or with PCR can they be differentiated from Ta2.  However, if Green Mold rapidly grows across the growing surface or is found in the compost below, it is most likely the aggressive Trichoderma Green Mold, Ta2.  Another sign of Ta2 infestation is the presence of pygmy mites, though this is not always true, as they feed on other fungal molds that grow in the mushroom substrate.

The mechanism of pathogenesis of Trichoderma Green Mold on mushrooms is not completely known.  Some Trichoderma spp. produce toxic metabolites that inhibit the growth of other organisms, and some species can parasitize the mycelium directly.  Most evidence so far suggests that Ta2 produces metabolites that inhibit the growth of A. bisporus (Mumpuni, et al., 1998, Krupke, et al., 2003). Electron microscopic observations of the interaction between Green Mold and mushroom mycelium did not show any obvious pathogenicity (Anderson, et al., 2001).

Disease Development

Disease severity or timing of the disease signs and symptoms on a farm may be related to several different circumstances or combinations of these factors. The number of spores and the timing of infection determine when Trichoderma Green Mold will first appear in a crop. An early infestation and/or a high spore load at spawning will result in early signs of the disease, and the severity will most likely be serious. Whereas a later infestation, as before or at casing or a low spore load, will result in the disease developing at or after 1^st break and usually with less severity.

Observations made over the years at farms in Pennsylvania and elsewhere have suggested that certain mushroom composting (Phase I and/or Phase II) conditions were often associated with Trichoderma Green Mold disease development.  The occurrence of Trichoderma in farms with high sanitation levels appears to be associated with compost that is not nutritionally selective for the mushroom mycelium. Wet compost, which was poorly aerated during Phase I and/or Phase II, is often associated with increased disease severity or incidence on the farms.  Both H. Grogan (personal communication) and Beyer (2008) reported that compost prepared under low-oxygen conditions was more susceptible to disease development.  Under these low-oxygen, or anaerobic, conditions, bacteria produce organic acids, which may persist during the substrate preparation process and remain residual after it, when the mycelium of A. bisporus is seeded into the substrate.  It has been reported how organic acids encourage the growth of T. aggressivum (Figure 2). 

Therefore, the compost's susceptibility and spore load may determine when the disease develops and how severe it may be. Figure 3 shows the relationship between spore load and the susceptibility of compost. So, a well-conditioned substrate with proper moisture may be less susceptible, but with a high spore load at infection, the disease could develop relatively early, with possible mild to high severity.  That same scenario may occur with a low spore load infecting a highly susceptible compost.

The spawn grains also play an important role in the initial infection of a crop.  The grain carrying the mushroom mycelium appears to be a good source of food or may stimulate Trichoderma spore germination. Protecting the spawn grain with fungicide or using a non-grain spawn reduces the early disease development and severity.

Trichoderma spores introduced onto a fully colonized substrate tend not to cause serious disease.  However, bulk spawn run compost (Phase III compost) that is broken up when filling a truck or when placed on farm shelves can be very susceptible to Trichoderma infection.  It is assumed that the sugars and carbohydrates within the mushroom mycelium are released when it is broken up, and that these carbohydrates are a readily available source of food for Trichoderma.

Once Trichoderma mycelium begins to grow, it will quickly spread through the compost and casing, and the A. bisporus mycelium will no longer be able to grow there. Trichoderma will spread across the growing surface and continue to sporulate, producing as many as 1,000,000 spores per 1 gram of casing in as little as 24 hours. These spores then serve as inoculum for the next crop or for new rooms.

Control

Disease control depends primarily on reducing or eliminating spores through sanitation and vector control. Trichoderma spores are vectored around the farm in many ways. The spores can adhere to employees, their clothing, and the farm's equipment. Flies, mites, and rodents can also spread the spores. Mites are good secondary vectors because they have specialized structures, called sporangia, that carry and spread spores.

Wooden shelves and trays in crops heavily infested with Trichoderma Green Mold can become impregnated with the Trichoderma mycelium, (Figure 4).  If post-crop steaming and Phase II pasteurization are insufficient, that mycelium will be a source of infection in the subsequent crop planted in that room. In addition, Trichoderma spores may survive lower temperatures or shorter post-crop steaming times and infest subsequent crops. A proper Phase II pasteurization with good ammonia concentrations in the air and substrate appears to be effective in killing the spores.

Using a mapping technique to monitor Trichoderma spots after casing through cropping may help determine the source of infection. By monitoring the number and location of the infections, it may be possible to detect a pattern or time of infection.  Improperly sanitized spawning equipment may show up if the disease has its highest incidence in the area where the spawning crew starts or in the first trays to be spawned. Mapping the movement of compost from a bulk tunnel into the farm's shelves may also reveal a pattern of infection during tunnel spawning (Obrien et al., 2017). High Trichoderma counts in rooms or areas with the highest fly populations could indicate that spores are entering with flies (Coles et al. 2021). It has also been reported that shelves filled by hand had a higher incidence of Trichoderma in the lower beds than rooms filled with nets (Coles et al., 2024).  They related this pattern to employees having to step from the floor into the lowest bed while filling it.

Equipment and personnel from infested crops should be prevented from entering the spawning or casing areas during those operations. Additional steps, such as issuing new uniforms daily to spawning personnel and separating cafeterias and break rooms for employees working in the spawning and casing areas, are effective.

Although Trichoderma spores are not easily airborne, dust particles and flies can carry them, so filtration and air pressure during the spawning and casing operations are critical. Maintaining positive pressure in a spawning area or room would help reduce the risk of contaminants from vectors contaminating a fresh substrate.

To reduce the spread of spores within an infected crop, cover all spots of Trichoderma with either salt, hydrated lime, gypsum, or alcohol.  Whatever is used should cover several inches beyond the infected area.  Usually, the substrate under the infected area is greater than what is seen on the casing, so extending the covering material beyond what is seen will help prevent new areas from developing from the infected substrate below.

Existing registered chemical fungicides are ineffective in reducing or eliminating actively growing Trichoderma mycelium once it is established in the compost or casing.  Control is primarily good composting, complete pasteurization, a complete sanitation program, especially at spawning, and efficient post-crop steaming procedures. If this disease gets out of control, it is better to steam off the crop early to reduce the spore inoculum that could spread to subsequent crops.

References

Anderson, M. G., D. M. Beyer, and P. J. Wuest. 2001. “Yield Comparison of Hybrid Agaricus Mushroom Strains for Resistance to Trichoderma Green Mold.” Plant Disease 85: 731–734.

Beyer, D., K. Paley, J. Kremser, and J. Pecchia. 2008. “Influence of Organic Acids on the Growth and Development of Trichoderma aggressivum, a Pathogen of Agaricus bisporus.” Pages 540–555 in Science and Cultivation of Edible and Medicinal Fungi: Mushroom Science 17, edited by Van Gruening. Pretoria, South Africa: South African Mushroom Farmers Association. Proceedings of the 17th International Congress, Cape Town, South Africa, May 20–24 (CD-ROM).

Coles, Phillip S., Maria Mazin, and Galina Nogin. 2021. “The Association Between Mushroom Sciarid Flies, Cultural Techniques, and Green Mold Disease Incidence on Commercial Mushroom Farms.” Journal of Economic Entomology 114 (2): 555–559. https://doi.org/10.1093/jee/toaa322.

Coles, Phillip S., Milton E. McGiffen Jr., Huaying Xu, and Moises Frutos. 2024. “Compost Filling Methods Affect Green Mold Disease Incidence in Commercial Mushrooms.” Plant Disease 108 (3): 666–670. https://doi.org/10.1094/PDIS-06-23-1101-RE.

Krupke, Oliver Albert, Alan J. Castle, and Danny Lee Rinker. 2003. “The North American Mushroom Competitor, Trichoderma aggressivum f. aggressivum, Produces Antifungal Compounds in Mushroom Compost That Inhibit Mycelial Growth of the Commercial Mushroom Agaricus bisporus.” Mycological Research 107 (12): 1467–1475.

Mumpuni, A., H. S. S. Sharma, and A. E. Brown. 1998. “Effect of Metabolites Produced by Trichoderma harzianum Biotypes and Agaricus bisporus on Their Respective Growth Radii in Culture.” Applied and Environmental Microbiology 64 (12): 5053–5056. https://doi.org/10.1128/AEM.64.12.5053-5056.1998.

O’Brien, M., K. Kavanagh, and H. Grogan. 2017. “Detection of Trichoderma aggressivum in Bulk Phase III Substrate and the Effect of T. aggressivum Inoculum, Supplementation and Substrate-Mixing on Agaricus bisporus Yields.” European Journal of Plant Pathology 147 (1): 199–209. https://doi.org/10.1007/s10658-016-0992-9.

Wuest, Paul J., and Glenn D. Bengtson, eds. 1982. Penn State Handbook for Commercial Mushroom Growers: A Compendium of Scientific and Technical Information Useful to Mushroom Farmers. University Park, PA: The Pennsylvania State University, College of Agricultural Sciences.

What’s moving the mushroom industry right now?

The mushroom sector continues to evolve at pace. Automation, labour availability and cost efficiency remain dominant themes, while growers balance innovation with reliability on the farm floor.

Below are a few developments worth watching.

1. Automation: progress, but not autonomy

Robotics in mushroom harvesting keep improving, yet fully autonomous solutions are still limited in peak and variable flush conditions. As a result, more growers are exploring hybrid harvesting models, where technology supports – rather than replaces – skilled labour. The focus is shifting from “full automation” to consistency, ergonomics and uptime.

2. Labour strategy is becoming a technical issue

Labour shortages are no longer just an HR concern. Growers are increasingly looking at technical solutions to:

• reduce physical strain
• stabilise output quality
• make harvesting work more predictable

This is influencing investment decisions in equipment, layout and workflow design.

3. Data-driven growing gains traction

Yield tracking, flush performance analysis and real-time monitoring are becoming standard tools for larger operations. What stands out: growers are less interested in dashboards, and more in actionable insights that support daily decision-making on the farm.

4. Sustainability: from ambition to optimisation

Rather than big sustainability claims, the conversation is moving toward practical optimisation:

• energy efficiency per kg
• smarter use of substrates
• longer equipment lifecycles

Incremental improvements are proving more impactful than radical overhauls.

What to watch next

In the coming months, expect more discussion around:

• hybrid harvesting as a structural solution
• the ROI of semi-automation
• technology that adapts to biological variability, instead of forcing uniformity

We’ll continue to follow these developments closely and share insights that matter to growers, farm managers and technology partners.

GrowTime recently showcased its high-performance automation solutions during the Umdis mushroom cultivation course at the Marczak mushroom farm in Poland.

Participants could see a presentation of GrowTime lorries equipped with the MycoSense Spotlight system working in real conditions on the farm.

A major highlight was the “smart speed control” feature—an intelligent speed management solution developed through close collaboration between the MycoSense and GrowTime teams. This kind of automation is designed to boost productivity while keeping daily operations more predictable and easier to manage.

It also supports a higher level of workplace safety and helps extend equipment durability in demanding farm environments. With better control over production processes, farms can improve efficiency and see a measurable impact on profitability.

Read the full recap and watch the event video in the article here.

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As a mushroom and compost consultant, I receive more questions from clients who have already searched for answers using ChatGPT. Often, they are not looking for a new solution, but for verification of what they have found online. This already shows how widely AI tools are being used in our industry. I use ChatGPT myself on a regular basis. It helps me write reports and articles that are clearer and easier to read, and its English is certainly better than my own “Dunglish” (20% Dutch, 80% English).

For collecting information about composting or growing issues, ChatGPT often provides useful insights. The answers are not always fully correct or directly applicable in practice, but they usually point in the right direction and help identify which area needs further investigation.

Modern mushroom production requires precise control of both composting and growing processes. Small variations in raw materials, fermentation, climate, or handling can have a significant impact on yield and quality.
While practical experience and on-site expertise remain essential, digital tools such as ChatGPT can support growers and consultants with faster analysis and better-structured decision-making. In cooperation with a compost and growing consultant, ChatGPT functions mainly as a knowledge-management and support tool. Combined with biological understanding and field experience, this approach can help improve compost consistency, crop stability, and overall production results.

Total Mushroom Service
Jeroen van lier
( 80%) Chat GPT (20%)

Why collaborative robotics make sense in mushroom production

What happens when humans and robots harvest side by side? Not in theory, but in the real, high-pressure reality of mushroom farms, with variable growth, peak flushes, labour shortages and razor-thin margins.

Hybrid harvesting, also known as collaborative robotics, is gaining ground precisely because it doesn’t pretend farming is predictable. Instead of forcing full automation before the technology or the farm is ready, it offers a practical middle path, robots and people working together, each doing what they do best.

For many growers, that balance is exactly what makes automation finally workable.

Why hybrid harvesting matters right now

There is a growing consensus in the industry that fully autonomous harvesting is not yet a universal answer. Mushrooms don’t grow the same way twice. Flushes vary, beds behave differently, and peak moments can overwhelm even the fastest machines.

At the same time, labour pressure continues to rise. Growers are looking for solutions that reduce dependency on manual labour, without taking on the risk of an all-or-nothing automation leap.

Hybrid harvesting answers that tension. It allows farms to automate step by step, task by task, proving value along the way, while keeping humans involved where flexibility, judgment and backup capacity are essential. In short, it lowers risk, increases resilience, and makes automation adaptable to real farming conditions.

What hybrid harvesting actually means

Mycionics defines hybrid harvesting as giving growers control over how much of the harvesting process is done by robotics and how much by people, and being able to adjust that balance when conditions change.

In practice, many robotic systems can handle around 70 to 80 percent of the physical picking work. But the remaining portion often determines profitability, especially during peak flushes, selective picking moments and quality-critical decisions.

Hybrid systems are designed to absorb those fluctuations. When robots reach their maximum capacity, human pickers can seamlessly augment the process. When labour is scarce, automation takes the lead. The system does not fail when reality deviates from the average.

Designing for reality, not perfection

A key reason Mycionics chose a hybrid path is simple. In complex environments, trying to be cheaper, faster and better at the same time usually leads to compromises elsewhere.

Mushroom harvesting involves thousands of micro-decisions per shift. Where to go on the bed. Which mushrooms are at the right stage. How to pick without damage. Where to place product. How to manage containers and flow.

Humans are strong in judgment and adaptation. Robots excel at consistency, precision and repetition. Hybrid harvesting assigns each role accordingly.

Mycionics’ proprietary vision, decision support and crop-intelligence system identifies mushroom size, predicts growth and determines optimal picking moments. These decisions can then be executed either by robotic arms or by human pickers, removing cognitive load from people while preserving flexibility. The result is faster picking, better timing and more consistent quality.

From scanning to packing, a modular approach

Hybrid harvesting does not start or end with picking.

Pre-harvest scanning maps pinned beds, tracks growth over time and predicts when and where harvesting should begin and how to adjust environmental factors to boost yield. Crop Scout guidance points human pickers to the mushrooms that should be harvested first, eliminating guesswork and increasing efficiency.

Robotic harvesting units mounted on drawers or lorries can handle large volumes, placing mushrooms onto belts, conveyance systems or directly into containers. During short, intense flush periods, humans can work alongside the robots to temporarily increase capacity during separation.

After picking, packing makes up about 50% of the labor cost in harvest. Robotic packing systems automate one of the most labour-intensive stages, improving weight accuracy, reducing giveaway and maintaining best presentation quality – “cheaper faster better”!. Because all modules share the same vision and intelligence backbone, growers can scale gradually, investing when confidence and return on investment make sense.

Measurable impact on farms

Early results in side-by-side comparisons on neighboring beds show why this approach resonates. Where growers are using crop intelligence and guided picking see around 15 percent improvement in labour efficiency and 10 to 15 percent yield improvement through better harvest timing.

With robotic harvesting, up to 75 percent of picking labour can be automated using multi-arm systems, with human support during early separation days to set the bed for full automation. Robotic packing significantly reduces labour demand in a stage that often represents around half of total harvest labour costs.

Beyond the numbers, growers value something less tangible but equally important. Systems that keep working when conditions are not perfect and never tire.

The role of AI, and where humans still matter

Machine vision and AI improve with data. The more cycles a system runs, the more accurate it becomes at recognising patterns, detecting anomalies and recommending actions.

Robots do not get tired or inconsistent. Over time, they become highly precise. Humans, however, still outperform algorithms in contextual judgment, especially when something unexpected happens. Hybrid harvesting acknowledges that reality instead of fighting it.

By collecting data early and continuously, growers build the foundation for smarter automation over time, without betting the farm on day one.

Looking ahead, hybrid as the bridge forward

Over the next three to five years, hybrid harvesting is likely to become the dominant automation model in mushroom production. Not as a compromise, but as a transition strategy that works NOW.

As technology proves itself in the field, confidence grows and returns grow. As confidence and returns grow, automation deepens. The system remains flexible, modular and grounded in farm realities.

The guiding principle remains simple. It has to work.

Born out of mushroom farming itself, Mycionics continues to focus on solutions that deliver value immediately, scale responsibly and strengthen the industry as a whole. There is no winner-takes-all model here, only progress that works when everyone can keep up with the harvest.  

E-nema will once again be present at the Mushroom Days in the Netherlands and that's good news for growers striving for strong, uniform, and sustainable crops. As a pioneer in biological crop protection, e-nema has been developing beneficial nematodes for over 25 years, which offer a natural solution to harmful insects in mushroom cultivation.

E-nema has developed a product line specifically for the mushroom industry aimed at effectively combating the sciarid fly (fungus gnat). These nematodes work deep into the substrate, actively seek out their prey, and thus significantly help control the population, without the use of chemicals.

At the Mushroom Days, e-nema will be happy to explain how these living organisms work, how they can best be applied, and the benefits growers experience in practice. Whether you're looking for a more sustainable solution, better pest control, or simply interested in the latest biological innovations, e-nema's experts are ready to answer all your questions.

Visit their booth and discover how natural enemies can be a powerful ally for healthy and future-proof mushroom cultivation.