Door Mark den Ouden,
mark.den.ouden@
mushroomoffice.com
In a tough spot PESTS AND DISEASES
Blotches and spots on mushrooms are a common occurrence. What kind of mark is it? Is it damage caused by a picker’s fingernails? Dry bubble spores on the cap? Trichoderma spores or bacterial blotch? And if it is a bacterial blotch, which strain? Is it Pseudomonas tolaasii, P. gingeri or P. solomonii (see also Mushroom Business 102). And how does bacterial blotch occur?
T
Pinning down the cause to a
bacterium is not the end of the story.
his article zooms in on the matter. Because can you get rid of those annoying blotches anyway? The answer to that is short and simple:
No! What you can do is prevent them and per- haps slow down the rate of development if you do have an infection. However, once you have noticed the problem, it’s already too late!
How to recognise blotch In laboratory conditions, increasingly advanced techniques are applied to diagnose the cause of blotches that affect mushrooms, but growers don’t have these techniques (yet). All a grower can rely on for diagnosis is their power of visual observation and the conditions in the growing room.
Lesions caused by dry bubble - scientific name Lecanicillium fungicola (the new name for Verticilium fungicola) - are also a problem you may encounter on mushrooms. They have a grey/brownish appearance, like the colour of a
normal dry bubble infection. You will rarely see these blotches unless you have a dry bubble infection. They are spores of bubble that develop on the mushroom and are visible on mushrooms that were in close proximity to a dry bubble infection, or in a growing room with a high infection density of dry bubble The spo- res continue to develop on the mushroom, even after picking. Just like ordinary dry bubble, these blotches can release spores! So treat mushrooms affected in this way as you would a dry bubble infection.
Trichoderma blotches Lecanicillium fungicola (Verticilium) lesions on mushrooms. 8 MUSHROOM BUSINESS
Green mould (Trichoderma) blotches are not always straightforward to identify. As the photo shows, they look brown/yellow. They are indented in the cap, as if the Trichoderma mould is eating it away. At another moment they look more like little ‘spots’ than real blot- ches and are darker brown. But as this photo shows, there is also a green mould infection. Sometimes you will notice the blotches on the mushrooms sooner than the green mould in the bed. But eventually you will always notice green patches of Trichoderma somewhere on the casing soil.
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