Plant material such as marijuana is an excellent food source for fungi such as Aspergillus. Once cut the material must be dried rapidly and consistently to a very low moisture level to avoid it becoming mouldy. Once dried it must be stored in completely dry conditions to prevent it becoming damp and once again quickly becoming mouldy.
Storing marijuana or any other plant material in small sealed containers or wrapped in plastic will only help if the material is completely dry in the first place, otherwise you are effectively locking the mould in with its own supply of food and water whereupon it will flourish. Mould does not need light or much heat to grow.