Powdery mildew on cannabis (PM) is a common growing problem. There are many methods for treating powdery mildew on cannabis. However, timing is ultimately the most critical factor. Furthermore, cleanliness, a well-thought-out growing setup, and attention to detail are key to resolving this increasingly common issue.
Fortunately, there’s no need to panic if powdery mildew starts to appear on your cannabis plants. Here’s why:
What is downy mildew?
Powdery mildew is a common fungal disease that affects cannabis plants. Two specific species of powdery mildew are capable of infecting cannabis: Taurica and P. macilans. Scientists classify these types of fungi as “obligate biotrophs,” meaning they require a host to spread.
PMs thrive in the warmer, more humid climates of places like Hawaii, Florida, and many southern states in the United States.
Once again, keep in mind that this is a common and treatable disease in cannabis plants. However, it is more difficult for a mature plant to recover from such a widespread infestation. Younger plants have a better chance of withstanding this powdery attack on cannabis leaves.
How does it harm plants? By weakening the leaves and slowing growth. Not ideal if you’re aiming for a high yield. Furthermore, the spores that develop as the cannabis plant flowers can contaminate the buds, rendering them useless. As such, you should treat powdery mildew on cannabis as soon as possible.
How to Identify Powdery Mildew
Powdery mildew appears as a gray or white powdery substance on cannabis leaves. Unfortunately, outdoor growers often mistake it for bird droppings until it’s too late.
Although you can remove powdery mildew from cannabis plants, you should do so with caution. Touching the powdery mildew could spread it and infect more plants. If you’re not sure whether you have a powdery mildew problem, ask yourself if the plant is struggling to grow.
Healthy cannabis plants are well-equipped to fight off pests. However, if the plants lack proper nutritionandbecome infected, the risk of disease increases. This is similar to the human immune system when faced with the flu or the current pandemic.
The environment in which plants grow can lead to powdery mildew in the following ways:
- Damp and humid conditions
- Stagnant water
- Stagnant air / poor ventilation
- Low-light greenhouse or indoor cultivation
- Dead or moldy vegetation
- Pest infestations
- Temperature
- Hot/dry weather
- Lack of environmental sanitation (more on this in the prevention section)
As such, it is essential to have a keen eye for detail. Even in a well-maintained environment, there is always a risk of PM. This is because it can occur at any time, sometimes without warning. Furthermore, PM thrives under the same conditions as healthy cannabis plants.
Fortunately, there are preventive measures you can take to avoid this problem. If powdery mildew on cannabis is a current issue, you need to address it now before it gets out of hand.
Treating downy mildew on cannabis plants
Treatment for downy mildew is most effective on young plants. It’s almost impossible to save mature plants, so time is of the essence. Fortunately, there are a variety of solutions available; the ones listed here are organic.
Ideally, you should avoid using chemical solutions. Since the plants are intended for human consumption, it is vital to resolve the issue without causing further problems for the plant or the consumer.
Since this is an urgent matter, start treatment as soon as you notice the problem. This process requires patience and may require several applications.
First, remove all leaves infected with powdery mildew that you cannot treat directly. Use clean gardening tools to prune and discard the leaves—DO NOT compost them! Next, apply a biological fungicide or make your own solution using diluted milk and a spray bottle. Simply mix 1 part milk with 9 parts water in a spray bottle. Using direct sunlight, spray directly onto the powdery mildew.
There are many organic fungicide options, including many items you likely already have at home. For example, hydrogen peroxide or apple cider vinegar work well for treating powdery mildew on cannabis. Other products include potassium bicarbonate, Bacillus subtilis, Streptomyces lydicus, Green Cure, and mixtures of vegetable oil with sulfur and garlic oil, cottonseed oil, or corn oil.
Methods for preventing powdery mildew
Preventing powdery mildew on cannabis plants starts with these key factors:
- Indoor growing or greenhouse setup
- Clear and reproducible procedures
- Macro-level pest management systems
The need for cleanliness is central to all of this. This applies to the environment as well as to anyone who interacts with the growing area. This means washing your hands regularly and, if necessary, changing clothes when entering and exiting the greenhouse or indoor facility.
You should also regularly sweep up fallen leaves, plant debris, and pollen, and never allow water to pool. Dispose of any infected plant material properly (again, do not compost problematic plants!). Use bleach to clean all walls and surfaces where fungi (and other pests) can survive.
This article from the Cannabis Business Times lists 11 key preventive measures against powdery mildew. These steps include:
- Use only clean genetics from reliable sources
- Sterilize the plants before placing them in quarantine
- Create positive-pressure environments
- Ensure proper airflow controlled by temperature and humidity
- Sterilize the air circulating in the grow room/greenhouse
- Clean ALL equipment regularly with hydrogen peroxide
- Make cleanliness a top priority at all times (be almost obsessive about it)
- Humidity Control
- Develop a decontamination procedure for all staff
- Establish a method for maintaining the temperature differential
- Find the "sweet spot" in the growing zone for vapor pressure deficit
Final Thoughts on Downy Mildew in Cannabis
Regardless of the producer’s level of experience, keep this information on file and monitor for any future issues.
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Have you had a run-in or two with this nasty, dusty fungus? What treatments worked (or didn’t work)? Leave a comment below and share your experience with other fans of our Swiss seed bank.
