- Botrytis is a fungus that frequently affects cannabis crops. As with most fungi or fungal diseases, it is often better to prevent them from occurring in the first place rather than having to deal with them once they appear.
- This fungus thrives in high humidity and is also opportunistic, as it uses certain animals or insects as vectors to spread, ultimately continuing its growth or spread onto your cannabis plants.
1. What exactly is botrytis, or gray mold, in cannabis plants?
2. How can you prevent botrytis from developing in a cannabis crop?
3. The Importance of Keeping Tools and the Growing Area Clean
4. Keep insects away from cannabis plants
5. How can you identify botrytis in a cannabis crop?
6. How do you get rid of botrytis?
Botrytis is a pathogenic fungus also known as “gray mold”; It is simply a fungal disease capable of affecting your cannabis plants at any time, although certain climatic factors favor its onset and spread, such as high humidity, which can be caused by heavy autumn rains or sudden changes in outdoor temperature.
The flowering stage is a delicate period, especially when growing outdoors, as our precious, high-quality buds could suffer permanent damage at any moment. Apart from weather conditions, there are other factors that can facilitate the potential onset of botrytis, such as the presence of insects like caterpillars near the plants, for example, since their excrement promotes the presence and development of this fungal disease.
Once the fungus has taken hold, it’s not that easy to get rid of it. It’s always best to prevent fungal diseases like powdery mildew, downy mildew, Fusarium, or Alternaria from infecting your cannabis plants. Learning to recognize and distinguish these fungal diseases is essential for any serious grower, as downy mildew and powdery mildew share similar characteristics but are actually quite different.
That is why you should always use high-quality soil and take care to maintain soil health and root health. If you notice spots appearing on the leaves, this is always a sign that something is wrong. It may indicate certain nutrient deficiencies or be a sign of visible mold.
One thing is certain: the damage caused by all these pests can have serious consequences if not addressed in time. However, we’re offering some crucial tips that should help you prevent botrytis and eliminate it permanently, while protecting your harvest.
What exactly is botrytis, or gray mold, in cannabis plants?
Botrytis is, without a doubt, one of the most common fungi encountered in cannabis cultivation. Gray mold typically develops from plant debris, such as root, stem, and leaf remnants, or even dried flowers, that litter the ground. The mycelium—the vegetative body of the fungus, whose primary role is to facilitate nutrient uptake—is present within these plant debris.
Consequently, if the temperature rises, fungi or mold will thrive. This is also why spring and fall are the two times of year most conducive to the development of botrytis. This makes sense, since rainfall is particularly heavy during these two seasons, which naturally increases the risk of various types of mold forming.
During the day, the mycelium develops fungal structures called conidiophores. The conidia—the spores produced by these structures—are located at the tips of the conidiophores and are carried by the wind until they reach the leaves, stems, and flowers, where they eventually settle and continue their development or spread. Botrytis spores can remain dormant (in a state of latency) for many years without showing any symptoms, until favorable weather conditions finally arise, allowing them to reproduce and spread to new hosts.
How can you prevent botrytis from developing in a cannabis crop?
It is obviously best to prevent any infestation by this fungus by implementing certain preventive measures. The first important step is to always keep your growing area as clean as possible and never leave plant debris lying around.
Next, make sure your tools and equipment are always properly disinfected to prevent primary contamination through contact with other plants in your garden. If the cannabis plants are too close together, the disease will spread via spores, which will attach themselves to a new, healthy plant to continue their reproductive cycle.
The Importance of Keeping Tools and the Growing Area Clean
It is essential to always maintain impeccable hygiene in your growing area, as this is the first step in keeping botrytis away from your beloved plants. Also, be sure to thoroughly clean all your tools and growing equipment after each use with a strong disinfectant. We also recommend changing your clothes when moving from one area to another to significantly reduce the risk of contamination.
It goes without saying that when you notice a part of a plant showing symptoms of botrytis, you should remove it immediately, cutting away a few centimeters of the healthy tissue as a preventive measure. This is done to effectively eliminate and isolate any further infection by this pathogenic fungus.
Keep insects away from cannabis plants
Insects are the second major threat to our favorite plants, so it’s essential to keep them as far away as possible from our favorite pastime. Pests cause the same problems as fungi, meaning they jeopardize the healthy development of our beloved plants at every stage of growth—whether during growth, flowering, or in terms of both the quantity and quality of our harvest.
All of this is to help you understand that it is harder to eradicate them than to prevent them from appearing in the first place. It’s also worth noting that these fungi will infect new hosts more quickly if they’ve already been weakened by insect bites. Outdoors, we recommend applying broad-spectrum preventive treatments during the summer months to limit the presence of caterpillars during flowering, for example.
How can you identify botrytis in a cannabis crop?
It is true that it is not at all easy to identify the onset or early symptoms of this fungal disease during its initial stage of development in the buds. The earliest signs of infection are characterized by necrosis of the stems, branches, and leaves. This corresponds to the period during which the color of the infected tissue turns brown, with a moist texture, before the appearance of circular brown spots on the flowers, which will then turn gray, and finally result in noticeable drying out of the infected area. The affected area eventually appears dead.
How do you get rid of botrytis?
If you want to prevent botrytis in your marijuana crops, you’ll need to limit indoor humidity to a maximum of 60% during the last four weeks of flowering, as botrytis always occurs during this period. As we mentioned earlier, it is also necessary to remove all affected parts of the plant, cutting back a few centimeters of the healthy parts as a preventive measure.
One important thing to keep in mind is to lower the relative humidity to around 50–60% maximum, with an ambient temperature of about 26–27°C, to effectively dry out the indoor space. In the event that botrytis launches a sudden attack indoors, just as it would outdoors, you must quickly consider bringing the harvest forward; otherwise, you risk losing a significant portion of it.
If this fungus causes an infestation at the start of flowering, you can spray a solution containing beneficial antagonistic fungi such as Trichoderma harzianum, Ulocladium atrum or Gliocladium Roseum on each marijuana plant. This type of treatment should stop the growth of this mold fairly quickly.
Once again, prevention is key: make sure you consistently maintain the right environmental conditions (temperature, humidity) and uphold impeccable hygiene standards. These are the key factors for a successful harvest, whether you’re growing indoors or outdoors. If you choose to grow outdoors, the first major factor you need to give serious consideration to is selecting high-quality cannabis seed varieties to purchase.
It is true that mold problems generally arise in late summer or early fall, when marijuana plants are in their final weeks of flowering outdoors. The large amounts of water produced by these rains over a fairly long period, combined with potentially poor air circulation and thus extremely high humidity levels around the dense buds packed with resinous trichomes.
Now imagine that we’re growing hybrids or Indica-dominant strains under these conditions—that’s when we’re faced with a serious problem. That’s why, once again, choosing the right cannabis strains for your seeds is absolutely crucial. We recommend pruning your plants, particularly removing any leaves that block airflow within the structure of each marijuana plant. This is clearly a factor that can facilitate the spread of mold.
These can also block the passage of light, thereby limiting the formation and weight of your crop’s heads. Furthermore, as temperatures drop in early to mid-September and humidity levels rise due to autumn rains, it makes sense to reduce the amount of water in the soil during watering in the final weeks, since evaporation is no longer the same as it was during the hottest days of summer. On the other hand, this excess water in the soil could be fatal for our precious buds, because if our buds are very dense, the risk would be increased.
