Why do my oyster mushroom bags get green and black mould contamination?

Green or black patches are mould contamination, most often green Trichoderma or black bread mould, and they are the number one reason oyster bags fail. The usual causes are under pasteurised straw, too much moisture in the substrate, dirty hands or tools at spawning, old or contaminated spawn, and a dirty growing room with poor air. To prevent it, pasteurise straw properly by hot water or steam, drain it so it is moist but not dripping, do the spawning on a clean disinfected surface with clean hands, use fresh good spawn, and keep the room and racks clean and well ventilated. Remove and seal away any badly contaminated bag at once so spores do not spread to healthy bags. Avoid overcrowding and very high stagnant humidity. Good hygiene at spawning solves most cases. Your KVK can show the correct pasteurisation method hands on.