How To Avoid Powdery Mildew on Cannabis Plants

Powdery mildew cannabis
December 02, 2020

From afar, a White Powdery Mildew may seem like snow dust sprinkled on cannabis leaves. On closer inspection, though, the fungal disease is nothing close to a winter spectacle. It is a hungry, prolific pathogen that can take possession of a plant swiftly if not eradicated. That being the case, apart from preventing it from arising in the first place, taking the right action fast is most critical.

White Powdery Catastrophe

Similar to most types of cannabis-loving fungi, White Powdery Mildew is into giving surprises. Its spores can stay dormant while waiting for an opportune moment to attack. Then, once they attach to the flora, it’ll only take 3 to 7 days for the symptoms of infection to appear. The good news, though, is that this type of plant-pathogen is easy to spot and damages can be minimal if removed at an early stage.

What Is White Powdery Mildew

White Powdery Mildew On Marijuana

One of the most common fungal diseases in cannabis is White Powdery Mildew (WPM). It targets leaves and stems first, contaminating them with fluffy circular patches of flour-like substances. If not eliminated early on, more alabaster or gray blotches will appear, until they spread to the buds and cover the entire plant completely.

Like any other organisms, WPM aims to feed and multiply. And, the fungus does so rapidly, as it can propagate both sexually and asexually. Apart from diminishing the appearance of the cannabis, it also stresses the flora and weakens its health as it hinders photosynthesis. Moreover, if the precious colas get infected, they must be removed as the infection is most likely far worse than what it appears.

These are the signs of WPM occurrence to look out for:

  • The Cannabis plant looks like it’s been sprinkled with flour.
  • Circular spots that appear on leaves, stems, and buds have powder-like consistency.
  • Usually blankets the upper part of the leaves, but can be seen on the undersides too.
  • Leaves eventually turn yellow and dry out. In some cases, they may even twist, break, or become deformed.
  • If buds are infected, they may also become disfigured.

What Causes It

The spores that eventually turn into White Powdery Mildew often infiltrate gardens for both indoor strains and outdoor strains through the air, but can also be transferred by humans and pets. The fungus, though, cannot take hold of the cannabis until it is given an environment where it can thrive. These conditions set in motion a WPM problem:

  • High Humidity. Young cannabis plants need a moist home to grow and develop. When rooting seedlings and clones, humidity levels between 65 to 80% is ideal. Meanwhile, a 40 to 70% RH is optimal when floras are vegetating. Incidentally, WPM also flourishes in such settings. If the spores are present and the other contributing factors also transpire, the fungal disease will likely strike.
  • Lack of Airflow and Poor Ventilation. While high humidity allows the fungus to prosper, the lack of air movement and fresh breeze are what permit spores to settle. Therefore, a humid grow area needs proper ventilation with ample airflow to avert WPM.

Ways To Prevent Powdery Infestation

Although White Powdery Mildew is not the most challenging pathogen to eradicate, it is still best to prevent it from manifesting as to avoid stressing the cannabis. The great news is, fending off White Powdery Mildew requires no particular gadget or skill. Moreover, the same pre-emptive measures may also stop other fungal diseases from emerging.

Choose mildew-resistant or tolerant variants. Growing strains with strong resistance against mildew afford a good head start. Landraces accustomed to wet climates like Durban Poison and Columbian Gold are the best candidates. Meanwhile, hybrids such as Orient Express, Power Plant, and Super Silver Haze have mixed genetics from parents that do well in damp, humid settings.

Fine-tune humidity and airflow together. When it comes to adjusting humidity levels, the needs of the cannabis come first. For this reason, having a bit more vapor in the air is necessary at times. By ensuring proper airflow, though, the grow area remains unsusceptible to spore formation even when there are high amounts of moisture.

Secure these conditions for optimal humidity and breeze in a cultivation area:

  • Have a ventilation system that supplies fresh breath of wind and prevents stagnant air in a cultivation room.
  • Avoid overcrowding plants in tight spaces as that increases humidity and obstructs breeze.
  • Always prune away leaves that are not useful especially the ones in the undergrowth of the flora.
  • Shake off lingering water on the leaves or buds often caused by rain and condensation when growing outdoors.
  • Avoid overhead watering as that can also cause leaves and buds to retain H2O and increase humidity.
  • Only water when the lights are on or when the sun is up as doing so at night thickens the moisture in the air due to less evaporation.

Spray fungicide. Whether sourced from synthetic or organic sources, fungus-killing foliar liquid solutions make protecting cannabis from spores a lot easier. Spritzing these ingredients, sometimes with water or other infusions, can do the job:

  • Neem Oil
  • Baking Soda
  • Potassium Bicarbonate
  • Mouthwash
  • Apple Cider Vinegar
  • Sulfur and Lime
  • Milk
  • Garlic

Examine closely. Even if a cultivation area is fully automated, always have daily face time with the plants. Observe the grow medium, stem, leaves, and buds. If a blemish is found, use a magnifying glass or jeweler’s loupe for closer inspection to determine if it might be a WPM.

Control And Eliminate White Powdery Mildew

Part of responsible growing includes checking the cannabis regularly. If that task is executed strictly, there’s a nominal chance that White Powdery Mildew in the beginning stages will go unnoticed. Should the fungal disease manifest, here’s what needs to be done:

Cannabis Indoor Controled Environment

Assess The Damage

Take a good look at the plant and examine its overall condition. If the fungal disease has already spread in the buds, then the precious colas must be removed or the flora must be trashed altogether. On the other hand, if the infection is in the beginning stages, the cannabis can be saved.

Get Rid Of Any Trace Of WPM

Remove and destroy the heavily affected cannabis leaves first. Do not attempt to use or mix them on compost as the fungi will diminish the quality of the peat. Once that is accomplished, focus on the salvageable leaves. Wet a paper towel with water as damp material ensures that the spores cling to it and not spread. Gently wipe off the fungi from the affected area. During the whole process, make sure that the disposable handkerchief doesn’t touch any other part of the flora.

Secure Air Circulation And Ventilation

Pruning the inessential leaves away will allow better airflow. However, equipping the grow area with a ventilation system is also essential. The oscillating fan supplies fresh breeze in the grow room. Meanwhile, the extractor draws out the heat and excess humidity. Together, these two allow ample air circulation and provide an unfavorable living condition for the remaining spores, if there is any.

Treat The Cannabis

Spray a solution to the plant to protect it from another WPM attack. There are plenty of commercial fungi repellants available online and in gardening stores. However, going DIY and concocting blends will also do just fine. Here are some of the most effective home-made mixtures:

Primary IngredientRecipeFrequency of Application
Baking Soda2 tbsp for a gallon of water or 1 tbsp for a gallon of water with 1/2 tsp of liquid hand soapOnce a week
Neem Oil5 tsp for a gallon of waterEvery 7 to 14 days
MilkMix 40 parts milk with 60 parts waterTwice a week
Hydrogen Peroxide1 tsp for a gallon of 35% H202Not often / Only when necessary
Apple Cider Vinegar2 to 3 tbsp for a gallon of waterEvery three days

A Minor That Can Turn Major

White Powdery Mildew is preventable, perceptible, and not complicated to remove if detected at the outset. It seems like a minor horticulture concern compared to other pathogens that attack from inside-out. However, if not eliminated correctly and promptly, it can inflict significant damages.

Watering Cannabis Plant

Setting up a cultivation area that is unfavorable to the spores but also optimal for cannabis growth averts and stops WPM. Having said that, nothing beats giving regular check-ups as no invite is as tempting to spores as inconsistent supervision.