3) Second flush devoid of mushrooms.
4) Trichoderma on wooden pallets of spawn. Spawn producers should know better and switch to plastic pallets!
soil-borne pathogens such as Pythium, Fusarium, and Rhizoctonia. Trichoderma harzianum is applied in the soil, used as seed coating and applied as a foliar spray onto plants.
A versatile mould So why is Trichoderma so effective against other moulds, including our Agaricus? Trichoderma is a mould that commonly occurs in the soil and plays a crucial role in decomposing dead organic material. In this environment it is surrounded by a wide array of other moulds and bacteria. Throughout evolution, each organism developed its own strategies to survive and compete for nutrients. For example, actinomycetes are also active in the soil (familiar to us from the conditioning process). They are prolific producers of a range of antibiotics to destroy their competitors. Trichoderma, on the other hand, secretes enzymes such as chitinases and glucanases. These enzymes degrade the cell walls of moulds and produce hundreds of diffe- rent secondary metabolites such as steroids, polyketides and terpenoids that inhibit fungal growth. Trichoderma also physically attacks other moulds by coiling around the hyphae of the host fungi. Furthermore, it competes aggressively for the available nutrients because, like Agaricus, Trichoderma can degrade cellulose/ hemicellulose and lignin. All of this makes it a versatile mould capable of causing severe problems in the mushroom sector.
Biological balance Trichoderma will - normally - not grow in phase II compost (photo 1) because the antago- nistic biomass in the form of actinomycetes keeps it in check. That said, phase II compost can of course become contaminated and the Trichoderma spores will survive phase II. However, once the mushroom mycelium starts to grow, it produces peroxides that
destroy the surrounding biomass, paving the way for Trichoderma to quickly start becoming dominant. My own experience has also taught me that an anaerobic state (low oxygen) in the fermentation bunker is linked to major problems with Trichoderma afterwards. Apparently, this lack of oxygen stimulates the wrong (anaerobic) biomass that provides weaker protection. So does adding biological preparations to the compost contribute to preventing or controlling Trichoderma? Various bacterial preparations, often based on bacteria of Bacillus subtilis or amyloliquefaciens, are available that you can add to the compost. These are common soil- borne bacteria that grow in more oxygen-rich (aerobic) conditions. However, I believe it is more important to encourage a strong, healthy biomass in the compost to create a surplus of this type of bacteria, rather than adding a biological preparation.
How does a composting yard become contaminated? Contamination typically starts with a small green patch on the bed (photo 2). This creates confusion about whether the compost is the cause, or whether the root of the problem is on the farm. But some three weeks later, a serious outbreak of Trichoderma occurs, leading to the conclusion that the cause is the composting yard. Having visited mushroom growers with minor, major and devastating Trichoderma problems (photo 3), I believe there is a recurrent pattern: Firstly, a Trichoderma infection has to arrive at the composting yard from an external source. Once contamination occurs at the composting yard, it starts developing through internal cross-contamination. This can happen very easily. Research shows that as few as 80 spores per kilo of compost are enough for a visible contamination.
The presence of Trichoderma
Agressivium is feared in the mushroom
industry, and with good reason.
MUSHROOM BUSINESS 19
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