Powdery Mildew: A Clear and Present Danger to Your Marijuana Plants

Unfortunately, there are many trials and tribulations associated with growing marijuana. Your plants are always at risk of contracting diseases or falling prey to pest infestations during their growing cycle.

Powdery mildew is a fungal disease that can wreak havoc on your crop. However, it doesn’t have to ruin all your hard work! This article outlines what this disease is, how to spot and destroy it, and how to reduce the risk of it ever becoming a problem.

What is Powdery Mildew & Why Is It Such a Problem for Marijuana Plants?

Powdery mildew is an extremely common mold that impacts a variety of plants, including cucumbers and tomatoes. Unfortunately, this fungal disease also affects marijuana plants and can quickly become an issue since it enjoys the warm and dry environments in which weed thrives.

While breeders are working hard to create mold-resistant strains, powdery mildew remains a big problem regardless of whether you’re growing a handful of plants or engaged in commercial-scale cultivation.

You can generally spot it by the development of a gray or white crust covering your plants’ stems and leaves. Since powdery mildew spores are found everywhere, they are extremely hard to avoid.

To make matters worse, the spores spread easily and quickly, germinating and growing on the surface of your plants at frightening speed. Once afflicted, your plants will experience a slowdown in growth since the mildew hinders the process of photosynthesis. Your plants struggle to get the water and nutrients they need, leading to a marked decline in flower production.

In extreme cases, powdery mildew could kill your cannabis plants. This is mainly because the mold weakens your plants, ensuring they are at the mercy of pest infestations and other diseases.

Thus, it’s important to learn how to spot powdery mildew early before it gets out of hand.

What Are the Symptoms of Powdery Mildew in Marijuana Plants?

One of the most obvious signs of powdery mildew in cannabis plants is the appearance of white or gray patches on their stems and leaves. This sprinkling of white or gray resembles powder, hence the name. It can appear on the top and underside of the leaves, so make sure you check both sides regularly.

When powdery mildew begins to develop in your plants, you might see the following issues begin to take effect:

  • The leaves of the plants begin to turn brown or yellow
  • White spots from the growth of the mold appear on the upper side of the leaves
  • Plant growth begins to noticeably slow down as its ability to photosynthesize becomes compromised
  • The plant’s flowers don’t fully develop, stems become weaker and bend under the weight of flowers, and the leaves start curling
  • Leaves fall off plants; this is typically a sign that the plant has been damaged by powdery mildew for some time

How to Destroy Powdery Mildew

Given that this mold can cause serious, potentially irreparable damage to your marijuana plants, you need to act fast once you spot its existence.

You may be tempted to start trimming any affected leaves you see. The problem is that the powdery mildew spores will cover your hands, ensuring that you inadvertently spread the disease. Even if you manage to get rid of leaves covered in mildew, the mold will likely spread to the flowers. Unfortunately, you’re better served by removing affected plants from your indoor grow room and destroying them.

What Products Should I Use?

These days, there are a huge number of pesticides and fungicides available that can eliminate powdery mildew without compromising your crop. You can use the best products as treatments and preventative measures.

Depending on the product, you may need to spray it throughout the plant or apply it foliarly. Please ensure you carefully read the instructions on the label before applying any fungicide to your marijuana plants. That’s because the mix rate of water to fungicide can vary significantly from one product to the next.

In the case of mild powdery mildew, spray every plant in the grow room, as you have to assume that cross-contamination is an issue. From there, spray the plants once a week to prevent further powdery mildew growth.

If the contamination is more widespread, spray every plant and apply the treatment 24 hours later (unless the product label says otherwise). Check for further powdery mildew signs and spray plants weekly.

Please ensure that the lights and fans are off when applying the fungicide.

How to Prevent Powdery Mildew from Occurring

Prevention is better than cure when it comes to powdery mildew. Here’s how to reduce the chances of it becoming an issue in your marijuana grow room.

Keep Humidity in Check

When you grow marijuana indoors, there’s always a risk that humidity levels will prove problematic. This is especially the case when the lights are off because plant respiration is more pronounced at night when photosynthesis stops.

So, it’s important to check the humidity levels of your grow room, ensuring that the relative humidity (RH) remains at the 60% to 70% level during the vegetative stage. During flowering, the RH should be below 55%, although you should avoid allowing it to fall below 40% even in late flowering.

The onset of powdery mildew is more likely when humidity fluctuates significantly. When the lights are on, make sure your air conditioners are as well.

Monitor the Grow Room’s Temperature

Extreme temperature fluctuations also increase the risk of powdery mildew forming on marijuana plants. Ideally, the difference between the day and night temperatures within the grow room should be no more than 15 degrees Fahrenheit.

In general, you want the indoor grow room temperature to be between 68 and 80 degrees Fahrenheit. Issues can arise at night when the lights go off since the grow room temperature can fall rapidly.

At this point, the air holds less water, which gets released into the environment. The result is small pockets of excessive RH and micro condensation, which create the perfect breeding ground for powdery mildew.

Give Your Plants Enough Airflow and Space

If possible, invest in wall-mount fans for your indoor grow room. The continuous air movement they provide helps prevent powdery mildew from forming. Poor airflow to the corners of plants means that mold takes hold first.

You must also have enough space between your plants in the grow room. One good rule of thumb is to ensure there aren’t more than four plants per light. There’s no point trying to squeeze lots of plants into a garden if doing so reduces yield per plant.

Provide Adequate Nutrients

Strong and healthy plants are less likely to be attacked by pests and diseases such as powdery mildew. Thus, you need to provide your crop with enough water and nutrients throughout its life cycle. Overly stressed plants are more susceptible to infections, so bear this in mind at the start of your grow.

Apply Natural Fungicides

You should also consider applying natural fungicides during the growth cycle to prevent powdery mildew. For example, neem oil does a great job of preventing pests and diseases from damaging your plants. You can mix a gallon of water and three tablespoons of oil and apply the mixture to both sides of the leaves once a week.

Some growers add products that contain potassium bicarbonate to increase the pH level of the leaves surface. However, you should avoid this process during the flowering stage, as it can negatively affect the quality of your marijuana.

Keep Powdery Mildew at Bay and Enjoy Healthy, Happy Marijuana Plants

Powdery mildew is a common problem faced by marijuana growers. If left untreated, it can cause untold damage to your crop. Fortunately, if you learn how to spot it early, you can quickly remove it and save your plants.

However, it’s best to prevent it from ever becoming an issue, so give your plants space and air, manage the grow room’s temperature and humidity, and consider regularly applying natural fungicides for maintenance purposes.

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