Powdery mildew is one of the most common fungal pathogens found in cannabis crops. It is a fungal disease that can have disastrous consequences, as is also the case with potential infections caused by Botrytis, downy mildew, Pythium (damping-off), Fusarium, or Alternaria, if preventive measures are not taken in advance. It is far better for this type of mold to attack your plants during the growth stage rather than during flowering.
Powdery mildew is a fungal disease that is fairly easy to control indoors during the growing season; however, it can become a problem if the fungus appears during flowering. In this blog post, we offer some helpful tips to help you clearly identify powdery mildew, prevent its occurrence, and, most importantly, determine which treatment to use to eradicate it from your favorite garden.
- What is powdery mildew?
- How can you tell if powdery mildew has appeared?
- How can you prevent powdery mildew from developing?
- Treatment using natural products to eliminate powdery mildew
What is powdery mildew?
Powdery mildew is a fungal disease that is naturally similar to plant rot, as it clearly belongs to the category of molds or fungi that affect cannabis plants as well as many other plants. It is a fungal disease that attacks both indoor and outdoor cannabis crops, where the natural environment makes it easier for the fungus to thrive, particularly with the onset of fall weather conditions.
This is a time of year marked by cooler air temperatures and heavy rainfall, resulting in high humidity. This does not bode well for the end of the flowering period of our favorite strains; in fact, it is an ideal time for powdery mildew infection, as the flowers swell rapidly and produce a significant amount of resin trichomes at this stage.
If you notice that a plant has buds infected with this fungus, you should remove them immediately and under no circumstances consume them, as this could cause serious respiratory problems.
How can you tell if powdery mildew has appeared?
Powdery mildew is a fungal disease that is easy to identify due to the circular white spots that gradually appear on the upper surface of cannabis leaves. In addition, a white powdery residue forms on these spots, resembling plant debris that looks like flour. As the fungus spreads, the spots multiply rapidly and colonize all parts of the plant (leaves, stems, branches, and flowers).
The critical stage is reached when powdery mildew spreads to the heads, particularly when it appears as a white coating on them, as this forces us to remove all parts affected by the disease and even some that are partially healthy but still show clear signs of infection. We therefore clearly understand that this can significantly reduce your crop yield.
It is essential to detect powdery mildew as soon as the first symptoms of the disease appear, because if you don’t take the right steps at the right time, this fungus could destroy your entire crop. The more the infection spreads and the more time passes, the harder it will be to eliminate these fungi.
Be careful not to confuse it with downy mildew, which has fairly similar symptoms, except that downy mildew produces the same spots along with a white powdery substance on the undersides of the leaves as well. These same spots also take on a more yellowish hue as the disease progresses.
How can you prevent powdery mildew from developing?
Indoors
When growing cannabis indoors, we recommend maintaining the humidity level in the space between 45% and 60% at most. It is also important to ensure proper air circulation and adequate air exchange in the room. You should check that all fans are functioning properly, leaving no stagnant air pockets.
Be especially vigilant, particularly during the dark cycle, as the plants transpire quite heavily; it is therefore best to prevent condensation from forming, especially during the final weeks of flowering. When growing indoors, people often mistakenly believe that all equipment should be turned down at night; however, the opposite is true for our air treatment equipment, as its operation needs to be increased during these times.
Outdoors
If you’re used to growing cannabis outdoors, you’ll already have some experience with it. If, on the other hand, you’re just starting out, you’ll need to be extra careful in the spring, but also—and especially—as fall approaches. This change of season can come earlier or later than usual; unfortunately, it’s something we can’t control.
This change of season heralds the arrival of heavy rains, as well as a sudden drop in outdoor temperatures. These various climatic changes have a direct impact on the development of our beautiful, thick, high-quality cannabis flowers. This is why these fungi could affect all strains grown from high-quality Indica-dominant seeds, and why it is essential to select hybrids that are resistant to these diseases when making your purchases.
We also believe it is important to emphasize that all aspects of preparing the plant structure—particularly defoliation, which involves removing many leaves from the cannabis plants during the growing phase—are matters that require the utmost attention in order to avoid numerous problems later on.
This has a twofold benefit: it directly reduces moisture within the plant’s structure, thereby eliminating any risk of fungal growth by significantly improving airflow and light penetration—which effectively boosts the production of compact buds generously covered in resinous trichomes. Another unwanted problem could arise at the same time, as you might see insects or pests attacking your plants, which once again reduces your chances of a successful harvest.
It’s important to keep in mind that infection or contamination spreads very easily from one plant to another, as the spores of this fungus are highly volatile. They can therefore frequently settle on the plant’s leaves, stems, and branches—or, worst of all, on the precious buds of our beloved cannabis plants.
Growing cannabis isn’t always smooth sailing, as you’ll also need to thoroughly clean the area around your plants as a preventive measure—picking up all the fallen leaves and any other plant debris on the ground—to prevent this type of rot from causing problems for your CBD- or THC-rich cannabis plants.
This is a rather tricky phenomenon, as the spores are microscopic and therefore difficult to see with the naked eye. They are also highly volatile and can attach themselves to any part of the cannabis plant. It goes without saying that this could attract many harmful insects; as a result, you might end up with a second problem that wouldn’t be so easy to get rid of.
Prevention is always better than cure, as the saying goes, because the damage caused by these molds and pests is devastating to the successful cultivation of cannabis plants, which will ultimately yield delicious, fragrant flowers covered in a thick layer of resin. We can’t stress this enough: it’s crucial to prioritize your needs when selecting high-quality seeds from the very beginning.
Another point to keep in mind is that you should limit watering during the final weeks for two reasons: first, to maintain the vigor and health of your roots so they retain their full ability to absorb water, and second, because overwatering could lead to the development of mold. Also, be sure to avoid placing your plants in the shade when planting them in the ground. Leave a little space between your plants to ensure good, even air circulation around them.
Treatment using natural products to eliminate powdery mildew
We can’t stress this enough: prevention is always the best remedy against a fungus like powdery mildew, especially by avoiding the use of treatments during the flowering stage, which could compromise both the quality and quantity of your harvest. That is why we recommend that you always opt for a natural product, such as a biological fungicide, so as not to compromise the points mentioned above, but also—and most importantly—to ensure that the final product (the flowers) is safe for consumption and helps you maintain good health.
Using a mixture of water and milk can be effective during flowering, but its effects are temporary, as the fungus will reappear and continue to spread after about 6 to 8 days. Preparing this mixture is very simple: just mix 90% water (at room temperature) with 10% milk, and spray it directly onto the leaves and all parts of each infected cannabis plant.
You can also spray a mixture of hydrogen peroxide and water (60 ml per liter), which will have the same effect and last just as long as the milk-based treatment. Adding a beneficial antagonistic fungus to your soil or growing medium, such as Trichoderma harzianum is also an excellent idea, as it actively protects soil life and keeps your roots healthy. Purchasing an air purifier can also be beneficial, as it significantly improves air quality.
The use of propolis is also strongly recommended, as it significantly strengthens the immune system of many living beings, including humans. We must not forget its primary function, which is to protect the hive from various environmental threats, including pathogenic fungi such as powdery mildew or downy mildew, for example. To prevent these problems, always purchase the highest-quality cannabis seeds that are suited to your specific climate.
You can also find natural fungicides on the market, such as Oidioprot by Prot-eco, which consists of a blend of nutrients and microflora growth factors derived from extracts of specific microorganisms that ultimately prevent fungal growth. It is a non-toxic product that leaves no residues harmful to humans.
It is also possible to use chemicals to eliminate powdery mildew; however, it is essential to apply them only during the plants’ growth phase, as they leave significant chemical residues on the buds. Their use must therefore be strictly avoided during flowering, as this would render the harvest unfit for human consumption.
