Most people who grow cannabis aren’t thinking about mold at all! But there are 3 main types of mold that often attack unsuspecting cannabis growers…
- White Powdery Mildew
- Bud Rot
- Fuzzy White Mold (Regular Mold)
There’s so many other things besides mold to worry about during your grow, like nutrient deficiencies, plant training, bugs, increasing yields, increasing THC, etc.
But unfortunately, mold has a way of creeping into your life when you least expect it!
It’s possible to get mold at any point at any point in your plant’s life, but even if you make it through your entire grow without mold, the last 2 weeks before harvest (and the first few weeks after harvest) are actually the times when you’re most likely to get attacked!
This is extra frustrating because mold makes buds completely unsafe to smoke, and it most often gets you after you’ve already dedicated months and months of work into your grow. If you’re not careful mold can decimate your entire crop!
Where Mould Comes From
Moulds belong to the fungal kingdom, which emerged as a specialised branch of this family tree around 1.5 billion years ago. The 100,000 different species that have appeared since have adapted to their own unique surroundings.
For the most part, though, mould loves moisture, and it’ll go wherever it can find the most optimal conditions. That also applies to many plants, but, unlike plants, moulds don’t conduct photosynthesis. Instead, they require organic matter—which includes cannabis flowers—as an external food supply. Many of them also favour stagnant air, hence the proliferation of moulds in places like bathrooms and kitchen cupboards.
Spores and Reproduction
Moulds reproduce by sending out plumes of spores into the air. They can be likened to the seeds of a plant, although they behave in a very different manner. See, instead of sending out actual seeds, they wait for the moment they land in a prime environment. If that moment ever comes, they send forth hyphae into the world in search of food.
Some spores are asexual and successfully mate with themselves, giving rise to the next generation. Other spores create hyphae that require a mating partner. Hyphal cells from two different spores find each other and mate, and their nuclei merge, creating a zygote capable of further reproduction.
Causes of Mould
As we’ve mentioned before, mould will only start to infest, decompose, and damage cannabis plants when the conditions are just right. Mould spores exist in the air around us—and our plants—at all times.
Some species may lay dormant, only striking when the conditions fall in their favour. Other species wait, lurking in the soil, for the chance to start feeding on susceptible root systems. Many of them, as seasoned cannabis growers discover, occupy soil that favours their existence, making them very hard to tackle.
Although mould looks harmless—like you could clean it and forget about it—some species pose a real threat to human health.
Mould exists everywhere, to the point that all cannabis flowers will have a little (besides those cultivated in sanitised indoor spaces). Although mostly inert in small quantities, even tiny amounts of toxic mould can cause problems.
Now, most people possess a fully functional immune system capable of defending against occasional mould exposure. However, immunocompromised individuals are particularly susceptible to them, and prone to issues like lung infections when exposed to mould.
Common Types of Mould
While we’d like to only have to worry about one type, various species of mould could attack your cannabis plants. To ensure your crops stay safe, you and all other cannabis growers should get familiar with these common cannabis moulds. Even a basic knowledge of the traits, signs, and symptoms of these moulds will help growers prevent them, and treat them if they arise.
Botrytis (Bud Rot)
Botrytis, also known as grey mould, often enters plants through wounds and openings, although healthy specimens are also vulnerable.
Botrytis spreads through airborne transmission, and its spores are almost always present in the air. An open wound, or certain other conditions, will allow the spores to proliferate, potentially infecting entire plants and their neighbours.
- Small black dots begin to form on infected structures.
- Large fuzzy grey patches begin to form.
- Above-ground plant parts, such as buds and leaves, begin to shrivel, turn brown, and die.
- Leaf tips turn from green to yellow to brown as it progresses.
- Botrytis grows rapidly in humid environments.
- Damage that causes susceptible open wounds.
- Cool and humid conditions enable spread, mostly in spring and autumn.
- May occur as a result of poor storage conditions.
- Keep growing tools clean, especially before defoliation and pruning.
- Control indoor and greenhouse humidity levels using fans and humidity sensors.
- Prune visibly infected parts.
- Remove infected parts from the garden/property, and burn or bury them.
- Sterilise pruning tools after treatment.
- Equip the growing area with a fan, hygrometer, and sensor to prevent the humidity levels from reaching dangerous levels.
While they’re all referred to by one name, there are actually many types of powdery mildew. Whatever the species, though, they often occur on the foliage of cannabis plants, creating a fine dust-like layer of spores. The infection first looks like small islands of hyphae, eventually building into large patches that dominate the lower leaves.
The mycelium spreads over time, making contact with the branches, stems, and even the flowers. Then, in the advanced stages of infection, the mycelium starts to produce spores on the most compromised leaves.
- White, powdery patches of mycelium start to form on the fan leaves.
- Growth is stunted and leaves become distorted.
- Plant tissue becomes discoloured.
- Newer leaves and flowers appear infected.
- Environmental factors allow spores to germinate and hyphae to begin infecting plants.
- Powdery mildew thrives in high humidity and warm temperatures. Greenhouses, for example, provide the perfect environment for infection.
- Keep enough space between plants to prevent contact between them, which can enhance mildew transmission.
- Keep your grow room or greenhouse well-ventilated to keep humidity down.
- Use a dehumidifier if you’re growing in a particularly moisture-rich environment.
- Plant outdoors in the full light of the sun, if possible.
- Provide good soil drainage, and avoid overhead watering.
- Wipe down infected leaves with a wet paper towel.
- Use neem oil foliar spray.