White Spots on Marijuana Leaves

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    What Causes White Spots On Cannabis Leaves?

    White spots on marijuana leaves are a common issue facing cannabis growers. Two of the most common reasons for this are:

    • Fungal Disease-White Powdery Mildew is the most common type
    • Pests-Spider mite infestation Is the main culprit

    I previously wrote an article on spider mite infestation and control measures.  Therefore,  this article will mainly deal with the white powdery mildew spores on cannabis leaves. However, at the end of this article spider mites will be addressed.

    White Powdery Mildew On Pot Leaves

    White Powdery Mildew Infection
    Severe Case Of White Powdery Mildew

    A white powdery mildew infection is caused by mold spores spreading plant-by-plant. Your plants can be affected by a number of reasons, some of which are:

    • Wind
    • Air Ventilation
    • Pets
    • Any Even Humans

    How Can You Recognize A Powdery Mildew Infection on Leaves?

    In the early stages, WPM and a spider mite infestation can look familiar. As a result, it can be tough to find out precisely what problem you are having. It should go without saying that you need to know what an issue is before you can even think about solving the issue.

    White powdery mildew (“WPM”) is a fungus that causes the white spots to appear on cannabis leaves in its early stages. Initially, the lower plant’s leaves will be affected the most. As it gets worse, the spots will enlarge, and they will eventually turn into large circles, and the mold will ultimately spread to other areas of the plants. So, I will go over the primary signs that you should look for to determine whether you have a mite or a WPM problem.

    ● No Bugs Around- If, after careful inspection, you don’t see any bugs, other than fungus gnats, when your plants are covered with white dots, you likely are having a WPM problem.

    Fungus Gnat

    Fungus gnat from Commanster, Belgium 02

    ● Spot Appearances-WPM dots tend to look more like splotches or fuzzy circle patches on plant leaves. The pattern tends to be spotted, and sometimes wilted.  Please note, that you are looking for white spots. So, yellow spots or brown spots on the leaves mean you may have other problems than just mildew. (Yellow-spotted affected leaves are also called leaf septoria.)

    ● Leaf Appearance-The white spots are easy to spot as they stand out on the green marijuana plant leaves.

    White Powdery Mildew

    What Causes WPM And How To Best Prevent It

    The WPM dots (not caused by spider mites) most likely happen because of improper, indoor growing conditions. Some of the more common conditions which can cause the WPM dots to happen are the following:

    • Humidity-Humidity levels are around 70% is optimum for seedlings. However, humidity at around 70% is fertile grounds for WPM for plants and flowering. (That’s why you should never grow your seedlings together with your marijuana plants) So, you need to try to get the humidity levels down to at least 40% for flowering. So, regularly check your grown room humidity with your hygrometer.
    • Mold Resistant Strain-Consider is purchasing a cannabis strain that is resistant to mold. Click Here For a useful resource for mold-resistant cannabis strains.
    • Air Circulation– When you overcrowd your plants, you will be more likely to get WPM dots. So, you need to make sure that you evenly space out your cannabis plants and buy the correct size or grow tent for the number of plants you want to grow. Also, be sure to buy a quality circulating fan for your grow area and use it properly.
    • Not Enough Light-Your plants are susceptible to WPM when they do not get enough light. So, get a quality timer, if you don’t already have one. Also, you need to make sure that your timers are working and schedule them according to the particular strain you are growing.
    • Too Much Fertilizer WPM tends to like new plants, and over-fertilizing causes plants to grow too quickly. And your cannabis plants will be more susceptible to WPM when they are growing abnormally fast. Remember, too much fertilizer can be a bad thing. So, be sure to follow the recommended amount of fertilizer for the number of plants that you have.
    • Poor Air Quality-WPM fungus spores can spread more quickly if you have low air quality in your grow area. So, you would be wise to purchase an air purification system for your grow tent or grow area.
    • Water- A dry grow area along with high humidity can cause conditions that attract mildew. So, make sure your plants are properly watered.

    Why Should You Worry About White Spots on Fan Leaves?

    WPM starts out with the white dots on the top of your cannabis plants. If ignored, it will turn a white or greyish, mold, or fungi-like substance on your plants. Eventually, if left unchecked, the WPM will cover a large proportion of your cannabis fan leaves. The mildew covering makes it hard for your plants to get the amount of light needed for growth as it inhibits photosynthesis. The mold will eventually turn your plants yellow, then brown and your plants will untimely will die if you do nothing about the problem.

    How Can You Fix WPM

    There are several methods, both organic, DIY, and commercial, methods to fix WPM. I will go over each method. Above all, to lessen the damage, you mustn’t procrastinate. To reduce the damage, you need to fix the problem before your plants get any worse and that the WPM does not spread. Many of the solutions below can also be used to prevent WPM.

    DIY Methods For Fixing WPM

    • Baking Soda-Baking soda combined with liquid soap can serve as both a preventative and potentially help you fix a WPM problem. The recipe is simple as all you need is to add 1 Tbl spoon to 1/2 tsp to liquid soap (Make sure it is non-detergent dish soap) to 1 gallon of water.
    • Mouthwash– Mouthwash is designed to kill germs that cause cavities. The same properties in the mouthwash that kill germs also can work to help eliminate WPM. The formula is simply 3 parts of water to 1 part mouthwash. (Caution-be careful doing this when you apply this to younger plants as this is quite potent.)
    • Milk– Milk has surprisingly been found to help fix WPM. It is most commonly used for squash and cucumbers. However, you may want to experiment with this on cannabis. The recipes simply add 1 part of milk to 3 parts water.
    • Fungicide-Multiple types of fungicides are specifically designed to help you fix and prevent WPM.  The below fungicide, from Trifecta, is a top-seller on Amazon, and it is specifically claimed to help both prevent and fix WPM.
    Trifecta Crop Control Ready to Use Maximum Strength Natural Pesticide, Fungicide, Miticide, Insecticide, Eliminate Spider Mites, Powdery Mildew, Botrytis and Mold on Plants Non-Toxic 32 OZ Size


    The key to not having a problem with white dots on your plants, in the first place, is prevention. This means that you need to follow the best practices when it comes to indoor growing. First of all, especially if you are a newbie grower, I would consider starting out with cannabis strains bred for mold resistance. Then make sure you follow the best marijuana growing practices. I.E., Make sure humidity is at the proper levels, don’t over-fertilize, etc. Also, as an added bonus, it will likely not be as severe of an issue if you do use the best practices for marijuana cultivation if a WPM happens.


    How To Deal With Spider Mites

    Spider mites infestation is one of the most common pest infestations for cannabis. They can be recognized by their red/brown color, and oval shape. They are very small as they aren’t even 1/4 inches.

    They feed on the under part of the plant leaves by ingesting a plant’s fluids by piercing the leaf. Just like WPM, spider mite damage starts out with tiny white dots and if not treated the leaves will turn yellow and eventually die. They tend to thrive in a dry, hot environment. A neem oil mixture is one of the most common ways to treat this pest infestation. In another article, I go more in-depth with white spots on cannabis leaves caused by spider mites.


    Leaf Septoria-Is a condition caused by a fungus that initially causes yellow dots on your cannabis plants and as it worsens the spots will turn brown.

    Neem Oil-Neem oil comes from the neem tree and works for both preventing and curing pest infestation. It is the preferred organic, pest control solution, for marijuana growers.

    Organic Neem Bliss 100% Pure Cold Pressed Neem Seed Oil - (16 oz) High Azadirachtin Content - OMRI Listed for Organic Use
    Neem Oil


    Top 10 Newbie Friendly Cannabis Seeds

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