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Powdery Mildew

Powdery Mildew

While many hearty marijuana strains are resistant to diseases, most are still affected by fungal infections. One of the most common is called powdery mildew. In reality, powdery mildew is comprised of several fungi, and it can ruin a cannabis plant completely.

Powdery mildew is common in both indoor and outdoor cannabis plants. There are some very effective treatments that can get rid of it, but treatment needs to be administered quickly to prevent any lasting damage to the plant. Powdery mildew infects many types of plants besides cannabis, so growers will need to watch for this fungus on any plants in the area or in their house.

What is Powdery Mildew?

Powdery mildew, or white mold, is a parasitic fungus that first appears on leaves before spreading to the entire plant. It first appears as small bumps on the top of the cannabis plant’s leaves. As it progresses, it explodes into large patches of grey or white across the leaf.

Powdery mildew inhibits the plant’s ability to absorb light, therefore interrupting photosynthesis. While this can cause problems for the plant’s growth, it will also make the plant more susceptible to insect infestations and less capable of fighting diseases. While powdery mildew does not always kill a cannabis plant itself, it leaves the door open for other pests and pathogens to do so, and ruins any buds the plant develops. However, if left untreated, this dangerous fungus will cause a plant to die.

How Cannabis Plants Get Powdery Mildew

Powdery mildew is a pervasive fungus. Growing cannabis indoors limits a plant’s exposure to a lot of pests and diseases, but powdery mildew is nearly unavoidable. There are spores that free float in the air and spores that lie dormant on surfaces until a suitable host is available. Because of the prevalence of these spores, plants grown indoors or outdoors are susceptible.

Symptoms of Powdery Mildew

Powdery mildew issues progress quickly, so growers must check their plants regularly for signs of this fungus. If it is caught early enough, powdery mildew can be eliminated before it causes any significant damage. Below are the symptoms growers should watch for when checking for powdery mildew.

White Spots on Leaves

The most iconic symptom of powdery mildew is white spots on the leaves. Plants infected with this fungus will look as if they have been dusted with flour. The white spots will first appear on a few leaves before spreading to the rest of the plant.

Shriveled, Yellow Leaves

As the powdery mildew infection progresses, it will cause more damage to the cannabis plant’s leaves. They will change from a vibrant green to a yellowish color, beginning to shrivel. Eventually, these leaves will turn brown, dry out, and fall off of the plant.

When this happens, growers must take immediate action, especially if the plant is in the flowering stage.  If the fungus invades the cannabis buds, it is impossible to remove. The plant may die before the buds can finish growing, but even if they do not, they are likely already ruined.

Disfigured Leaves

In the event of a serious powdery mildew infection, cannabis leaves may be stunted and look deformed. Powdery mildew has a penchant for attacking younger plants, which will lead to disfigured leaves even after the infection has been eradicated. Young plants succumb to powdery mildew quickly if the infection is not taken care of immediately.

Preventing Powdery Mildew

Powdery mildew is easily treated once an infection has taken hold. However, there are some things growers can do to prevent a powdery mildew infection.

The first thing growers can do is choose a cannabis strain known to be resistant to powdery mildew and source seeds from a reputable online seed bank. Once they have a hearty strain of cannabis with strong genetics, growers can do the following:

Provide Ample Ventilation

Powdery mildew, like most molds, thrive in areas where the air is stagnant. Plants that are crowded with leaves and grow areas that have too much dead plant material around are perfect breeding grounds for powdery mildew.

Growers should prune their plants thoroughly, especially the leaves in the center, on the stalk of the plant. Doing this will encourage airflow around the plant and reduce chances of powdery mildew developing. Indoor growers should use fans to improve air circulation around their grow room.

Adjust the Humidity

Powdery mildew explodes in environments with humidity above 65% or below 40%. While this is difficult to control for those who grow outdoors in humid climates, growers who have indoor grow rooms can either use a humidifier or dehumidifier, depending on the conditions of their grow room.

Control the Temperature

Powdery mildew thrives in environments between 68 and 86 degrees Fahrenheit, specifically where the days are warm and the nights are cool. There is some evidence to suggest that temperatures above 90 degrees will kill powdery mildew, but this is not an ideal temperature for a cannabis plant, either.

Outdoor growers do not have as much control over the environment, but indoor growers can take some preventative measures. They should keep their grow room at a steady temperature at all times. Growers should be sure to check the room’s temperature often, so they can be sure to keep the temperature as stable as possible.

Water Early

Since powdery mildew thrives in cool, wet temperatures, growers must water plants when they have at least five hours of light or sun left in the day. Doing this allows the top of the soil to dry before night, when it is dark and, for outdoor grows, is cool outside.

Treating and Controlling Powdery Mildew

Outdoor growers cannot control the environment in which their plants are growing, and powdery mildew appears seasonally. These growers should focus on pruning, checking their plants for signs of powdery mildew, and eradication if an infection is present. Indoor growers still experience powdery mildew infections frequently, so they will need to learn about how to treat infected plants. If a grower sees any signs of powdery mildew, they should do the following:

Remove Infected Leaves

One of the first things a grower should do when they identify a few leaves with powdery mildew is remove them. They will need to carefully remove the infected leaves to avoid wounding the plant, and place them in a sealable plastic bag, then dispose of them away from the garden.

Growers will need to be careful that they do not disturb the leaves too much, as this could release more spores into the air, putting the other plants at risk of being infected by powdery mildew. If the infection is widespread and most leaves are covered, growers should not attempt to remove them. Doing so would leave the plant with too few leaves to sustain itself once the infection is gone.

Improve Growing Environment

Before using any fungicide solutions to treat powdery mildew, growers will need to check their growing area thoroughly for areas where spores may be concentrated. If growing indoors, growers should check to make sure their room has adequate ventilation, the temperature is steady, and the humidity is low. Growers should check for dead plant material, as this can be a breeding ground for powdery mildew and may infect plants again once the original infection is gone.

Use Organic Home Remedies

Growers who want to avoid using commercial fungicides can try several organic solutions that have proven to be effective in eliminating powdery mildew. These include:

Liquid Soap and Baking Soda Solution

One of the most popular organic methods of treating powdery mildew is using a solution of organic liquid soap, baking soda, and water. Mix about 1 teaspoon of liquid soap and 1.5 tablespoons of baking soda into a gallon of water and spray the plants liberally. This solution should be applied early in the day to avoid burning, and may need multiple applications.

Garlic Spray

Garlic spray is another common method of treating powdery mildew in cannabis plants, though it should not be used on flowering plants, as it will definitely alter the taste of the bud. Crush 2-3 cloves of garlic and mix it into a gallon of water with a few drops of organic liquid soap. This solution should be sprayed onto the plants in the same manner as the liquid soap and baking soda solution.

Neem Oil

Though neem oil is all-natural, it is a more harmful option, as it can be toxic to some mammals, birds, fish, and possibly humans. Mix one tablespoon of neem oil into a gallon of water and add a few drops of organic liquid soap to prevent powdery mildew infections. For active infections, growers should use three tablespoons of neem oil. Plants will need to be sprayed multiple times for it to be effective, and they should never be sprayed with neem oil during the flowering stage.

Apply Fungicides

Commercially available fungicides are available at most gardening stores, but growers should be cautious about which ones they use on their plants. Some are safe for ornamental plants, but could be harmful to other plants and animals, including humans. Always read the label on the bottle before purchasing and applying to cannabis plants.

Bottom Line

Powdery mildew is a widespread, common issue for cannabis growers. It is important to always keep a watchful eye out for an infection and address it as soon as possible. Fortunately, because of the prevalence of powdery mildew, growers have developed many effective treatment strategies to prevent and eliminate powdery mildew from cannabis plants. Following these techniques diligently will help you to reap bountiful yields from your healthy plants.