Powdery mildew is one of the most common cannabis plant infestations.
It’s difficult to foretell its presence, but once it arrives, it’s easy to spot.
The plant’s leaves will be coated in patches of white powdery substance which will reduce the rate of photosynthesis, stunt its growth, weaken its immunity, and expose it to more pests.
The infestation will eventually reduce your yield substantially— if you’re lucky to harvest anything at all.
While there are ways to treat your plants and get rid of the infestation, the best way to fight powdery mildew is to prevent it. The emphasis is on prevention because the powdery mildew spores spread quickly through the air, a slight wind can get your whole garden infested.
It also spreads by leaf contact, meaning if you grow your cannabis plants close to each other, when the affected leaves touch the healthy ones, the spores infect the healthy plant too.
Also, powdery mildew fungus thrives when your grow room conditions favor its spread.
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What causes powdery mildew in cannabis
Powdery mildew effects on cannabis can be detrimental to your plants. It just grows and spreads, and hurts your plants’ development.
If you spot it too late, especially at the flowering stage, it will affect the quality of your buds severely.
It is one thing for powdery mildew fungus to eat the leaves, but it is entirely a different level of destruction when they invade the buds— because you might not find a thing to harvest.
The white powdery mildew is caused by factors such as poor lighting, high humidity, leaf-on-leaf contact, poor airflow, and insufficient ventilation, as well as a combination of these factors.
Still, powdery mildew isn’t a death penalty for your cannabis plants. Experienced growers have ways of taming its aggression and possibly stopping it in its tracks.
For a novice grower, knowing what causes the problem goes a long way in fighting it. You know, you don’t want to be left with mildew-infested plants that your knowledge can’t allow you to remedy.
Here are the causes of powdery mildew to watch out for;
The powdery mildew fungus thrives in highly humid environments. Unfortunately, your grow room doesn’t have to be swampy to attract the fungus, high humidity is enough to necessitate its growth and spread.
While you can control humidity in your grow room by using dehumidifiers, young cannabis plants need high humidity (between 40%-60%) to thrive. And to think that they’re the primary target of this fungus is upsetting (the fungus begins by attacking young plant).
So how do you solve the puzzle? How will your young plants grow in the same favorable conditions as the mildew fungus?
Humidity is particularly easy to control for cannabis plants in the advanced growth stage. From veg to flowering, to harvesting, drying, and curing, you can control humidity by using dehumidifiers, thus making it easier to tame this malady.
Though the wing is the most common agent for spreading the white powdery mildew, your plants can also get it through leaf contact. The healthy leaf will get the spores if it gets in contact with an affected leaf.
Also, leaf contact can inhibit evaporation, trapping moisture between themselves, and creating the best environment for the spores to form. In this regard, an untrained cannabis plant is more likely to get the fungus than a well-pruned plant.
You can limit leaf-on-leaf contact by planting your plants far from each other. But also, you can defoliate the leaves that can’t access light as they are the major culprits.
However, it takes experienced eyes to know which leaves to defoliate— normally, the branches/leaves hold no promise of bearing buds.
By removing them, you’re not only helping your plant to fight white powdery mildew and other infestations but also saving your plant’s energy for flowering and bud formation.
Your plants need light to grow and have stronger immunity against pest and fungal infestations. Poor lighting can cause white powdery mildew because it reduces water loss and causes pooling in the soil.
Besides, when you don’t set your light the right way, some leaves won’t get access to the light, and thus promoting formation and proliferation of white powdery mildew.
I’ve already mentioned it; the combination of poor airflow and high humidity makes the perfect condition for the white powdery mildew to thrive.
While high humidity creates an enabling environment for the fungus to thrive, it is poor airflow that allows it to settle on the leaves. Use oscillating fans to enhance airflow in your grow room.
Also, keep your grow room as organized as possible. Don’t crowd it with tools, unused buckets, and other waste items as common with garage and basement grow spaces. Crowding interferes with airflow and creates dark spaces for fungal diseases to take root and thrive.
Your plants need fresh air. If the stale air is trapped in your grow room and it happens to have the white powdery mildew spores, they will spread multiple times in your grow room.
Eventually the spores will reach even the most spaced plants.
Invest in a reliable ventilation system that allows your plants to get a fresh breath of air. This way, the plants can feed off air that’s free from the fungus, but also, the ventilation gets rid of the stale, infested air, reducing the ‘fungal load’ in your grow room.
How to prevent powdery mildew in cannabis
Fungal diseases are pretty hard to deal with. Think beyond plants, if you have ever had any fungal infection on your skin, you’ll understand how hard it is to cure it.
Fungal diseases always have a way of returning, sometimes, in their most stubborn forms. White powdery mildew is no exception; once it occurs, it can easily reoccur if you don’t deal with it the right way. The easiest way to deal with the powdery mildew is to prevent it. Here’s how;
Space your plants well when transplanting
After germinating your seeds, space them well when transplanting. The closer they are to each other, the higher the chances of mildew infestation. Planting them closely increases the chances of mildew invasion of your grow room.
Planting your cannabis plant too close also makes it difficult to fight the disease because they are constantly in contact with each other. It is even worse when the infestation is advanced, trimming affected leaves of one plant doesn’t save the rest as the spores are easily trapped on the next plant.
Water your plants during the day
Watering at night isn’t a good practice, even if some growers do it. Watering your cannabis plants at night exposes them to wet ground for too long, exposing them to powdery mildew infestations.
Water during the day when you’re about to expose them to more than five hours of light. The exposure to light is essential in speeding up the evaporation and reducing water content, both in the soil and air.
Even for indoor plants, make a habit of watering during the day. It doesn’t matter if the plant will be exposed to light, the temperatures at night are generally low, leading to poor loss of water.
Trim bushy plants
Powdery mildew loves humid and warm conditions, and that’s the condition that bushy plants create. Untrained plants suffer poor light access and insufficient airflow, which further aggravates the ravages of fungal diseases.
Trimming your plants also limits cross-contamination through leaf-on-leaf contact.
Use powerful fans to promote air circulation
Fans improve airflow within your grow room. But they do more; they inhibit mildew infestation by limiting spores landing spots. They also improve water loss, reducing humidity.
You can also use one fan new the entrance to suck in fresh air while pushing the stale air out.
Grow strains that are resistant to mildew and other diseases
Some cannabis strains are more resistant to the powdery mildew fungus than others. If you live in a highly humid climate, you should try genetics with higher resistance to these fungal diseases.
If you’re just beginning, the ease of growing supersedes the promise of a huge yield— you want to grow strains that will resist diseases, and give you room for learning.
I wrote an in-depth article on strains that are beginner-friendly. Read through, you’ll get the best strain to grow in areas where powdery mildew is prevalent.
Maintain the optimum temperature and humidity
To combat white powdery mildew, you’ll need to find the right temperature and humidity for your plants, yet harmful to the fungus.
Cannabis plants will need high humidity while sprouting, after, you can lower humidity to up to 40% without harming your plants, this level of humidity won’t allow powdery mildew to thrive. Use a dehumidifier when necessary to keep humidity within range.
Cannabis plants thrive at temperatures between 60 and 72 F, and while too high temperatures can affect your plants, slightly increasing it to between 74 and 75 F won’t affect your plant severely, but will prevent the invasion of powdery mildew.
How to treat powdery mildew in cannabis
Well, if you have tried preventing this fungus, but it still reared its ugly head, you should now face it head-on.
If you’re learning how to get rid of powdery mildew during flowering or any other stage of your cannabis growing, we have solutions for you.
But first, remember the powdery mildew isn’t only harmful to the plant; it’s also detrimental to you. So gear up; wear your gloves and mask, then get to work.
Depending on the extent of the invasion, you might want to remove the powder from the leaves using a piece of cloth. When you wipe the powdery mildew with a piece of cloth and dump effectively, you limit their chance of spread as would happen when you sprinkle through a cloud of thick flour-like dust on the leaves.
After, you will use the right solutions to cure the plant. You can either use home remedies or use the commercial fungicides. Let’s begin with the home remedies;
Home remedies for removing white powdery mildew
If you love everything organic, and possibly detest the use of over the counter fungicides, you can use the following home remedies to cure your plant of white powdery mildew;
Using Milk– Mix 4-part milk and 6-part milk and use the solution to spray your plants leaves. The milk works wonders— upon exposure to light, the protein in the milk reacts with the light to form an antiseptic that kills the powdery mildew fungus.
You can also use milk as a preventive method by spraying your plant’s leaves after every ten days with a solution of 40% milk and 60% water.
Using Neem Oil- Neem oil is one of the best natural cures for powdery mildew infestation. Neem oil is an extract from the Neem tree that has been applied widely for medicinal purposes. Mix 4 teaspoons with a gallon of water and spray the whole plant with it.
Using Baking Soda- Baking soda is a common household item, but can also be used to fight fungal diseases in your plants. The powder, however, isn’t active on its own, you have to mix it with liquid soap and water to get rid of the fungus.
Mix 1 teaspoon of baking soda with 1 teaspoon of liquid, non-detergent soap and a gallon of water. Use this solution to spray your affected plants wholly.
Mouthwash- Surprised? Well, you shouldn’t be. Mouthwash is a potent solution that will not only kill the germs in your mouth but can also kill the white powdery fungus.
Mix with water; 30% mouthwash and 70% water, and use the solution to spray your plants. Though mouthwash is a good solution, it might interfere with new growth, so use it with moderation.
Vinegar: Vinegar is rich in acetic acid that’s harmful to the fungus. You can use apple cider vinegar which contains 5% acetic acid.
Mix 3 tablespoon of vinegar with a gallon of water and use the solution to spray your affected plants.
Using commercial fungicides to remove white powdery mildew
Though most people, including me, love using home-made solutions, sometimes it is the commercial fungicides that will remove the menace fast enough.
If the mildew has advanced, using commercial fungicides might be a reasonable thing to do as they work faster than most home remedies. When you can, use eco-friendly products so that you don’t degrade your environment.
Helpful tips for after you clear the white powdery mildew from your weed
The powdery mildew on marijuana, like all fungal diseases, can be hard to destroy. Even after you’ve saved your plants, you need to take care of your grow room so that the fungus stays dead.
Here are a few tips to avoid the shock of powdery mildew on cannabis at harvest;
- If you cut off the affected leaves, neither leave them on your garden nor dump them in the compost. Doing this will risk your plants as they might grow back to life and terrorize your next plants.
- You can replace the grow soil if you feel this fungus highly infested it. You can use other solutions to kill the fungus in the soil, but that might also kill the good bacteria. Therefore, if you deem fit, change the grow soil.
- Do not water the leaves. Watering the leaves might sound like a bright idea to keep them moist, but wet leaves are pretty good at trapping spores.
Growing healthy buds take a lot of time and resources. You don’t want to hustle all through it only to harvest powdery mildew on buds. Take good care of your plants; monitor their leaves, you might as well be lucky to spot the white powdery mildew before it destroys your plants. I hope you found this article helpful.
If you’ve dealt with white powdery mildew before, please share in the comments how you dealt with it, and if it affected your yield substantially.