Dried mycelium and/or small pins often occur when it freezes at night. The symptoms are caused by too much too dry air being blown over the beds caused for example by the minimum inlet position being set too high or the humidifier reacting too slowly. Mycelium is highly sensitive to dehydration during the blow down and pinheading stages. During this phase the casing soil is often still shiny with moisture. The mycelium has already suffered from a low RH combined with a higher fan position. Five to eight days later during the pin development stage the grower will notice that the casing soil surface dehydrates. This disturbs evaporation and causes pin growth to stagnate The whole process is slowed down and results in too few pieces and a first flush with too little or no spread This dehydrated casing soil is seen clearest at the edges of the shelves or trays where the air hoses hang.
Try to prevent this problem by working with a correct humidifier reaction time a lower minimum inlet position higher CO2-contents less aggressive circulation and possibly wetting the floors more frequently. Ensure the surface of the casing soil always feels cool and damp. If dehydration is noticed it’s a good idea to apply ½ to ¾ litres of water per square metre. Drying after spraying is usually not necessary Repeat this step twice if required.
Jos Hilkens, Advisie ‘The mushroom cultivation advisors’