Mould is the bane of any serious marijuana grower. It can easily decimate an entire crop. Fortunately, it is a problem which can be avoided and if it does strike, can be fixed, at least to a large extent.
Some strains have better resistance to mould than others
There are endless different varieties of marijuana and some are more robust than others. One of the most iconic marijuana strains, White Widow is known for having good mould resistance. Other options include Blueberry Widow, The Cheese, Holland's Hope and Golden Nugget.
Even the best strains still need good management
Preventing mould on marijuana plants is very similar to preventing it in a house. Try to reduce humidity and increase air circulation. Outdoor growers may have to hope that luck goes their way on this but indoor growers can use dehumidifiers and/or fans. Make sure there's a decent amount of space between the plans and if necessary trim them. Removing excess leaves will help improve airflow, but the effect will be completely negated if you simply put the leaves in a bin in the growing area. They need to be completely removed from the growing area. Mould also thrives in waterlogged soil so make sure your watering system gives the plant what it needs and only what it needs. Finally keep the growing area scrupulously clean. This starts with removing anything which could harbour mould so remove any fabrics and keep pets out (they can bring in mould on their coat and paws). Avoid using plastic sheeting as this traps moisture very easily and therefore attracts mould.
Chemicals can help in the fight against mould
Even if you are growing organically, you can still use mould-resistant paint in the growing area. You can also use disinfectant to clean surfaces such as floors. Cleanliness is a crucial aspect of mould prevention. For organic growers, there are copper- or sulphur-based sprays which can be used to protect plants before they start to flower. They are extremely toxic to humans if consumed and therefore must never be used on or near marijuana flowers. Rather ironically there are biological sprays which can be used at any time. Unfortunately combining organic and biological sprays would have far too strong an effect.
If mould strikes, nip it in the bud
No matter how many precautions you take, you still need to be constantly alert to any sign of mould. In particular you need to check your buds regularly. If you even suspect mould, you need to remove the affected part of the plant (or even the whole plant) from the growing area immediately.