Growers and pickers often encounter odd looking mushrooms during the harvesting period and in many cases they can be related back to crop management and watering management. These symptoms can include saggy stems, hollow stem, watery stems, discolored stems or weeping stems.


Scaley appearance on the cap surface. Can range from very mild with little effect on quality to very severe discoloration with the scales. Some strains are more susceptible than others. First flush mushrooms appear more susceptible than later flushes. The main cause is passing of dry air over the surface of mushrooms. Sometimes scales can be the result of ‘burning’ from water additives (e.g. hypochlorite, stabilised chlorine dioxide, calcium chloride) or from disinfectant vapors.


Distortions, lumps and gross malformations occur on the mushrooms. Often gills are present on the top leading to the name rosecomb. Cause: Contamination of the substrate with oil, diesel or distillate fumes.


Mounds of mushrooms that appear like cauliflowers. Usually they are the earliest mushroom picked.

Overlay or Stroma

A dense mass of mycelium growing on the surface of the casing. This often leads to reduced pinhead formation and interferes with watering because the mycelium ‘seals’ the casing so water cannot penetrate. Overlay is continued vegetative growth of mycelium in and over the casing. It can be caused by failure to initiate pinning early enough and/or not flushing hard enough (e.g. temperature and CO2 left ‘too high’ for ‘too long’). Stroma is a genetic malfunction in a spawn culture that is sometimes triggered by an environmental factor. It may also be found as dense mycelium growth observed in spawn bags and on top of substrate can be associated with problems in eh spawn making process or spawn transport. 

Carbon Dioxide Damage

Mushrooms with long stalks opening up small. Excessive Carbon Dioxide levels in the growing room and/or a crowded microclimate around the mushrooms that the CO2 can’t escape from. The symptoms of long stalks opening up prematurely can also be caused from water stress or virus.

Hard Gill or Pale Gill

Affected mushrooms have pale colored gills, white gills or gills can be non existent. These fruitbodies can be flatter than normal and have little or no veil. Cause can be genetic but usually it is from fluctuating conditions over a short period of time. White hybrid strains appear particularly susceptible in 3rd flush but all strains can be affected.

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