Comment traiter une attaque de botrytis dans une culture de cannabis ?

How to treat a botrytis attack in a cannabis grow ?

17/08/22Lu en 6mn
  • Botrytis is a fungus that frequently affects cannabis crops. As a large majority of cryptogamic fungi or diseases, it is often preferable to prevent their appearance, rather than having to eliminate this type of phenomenon.
  • It is a fungus that appreciates a high humidity level and which is also opportunistic, because it uses certain animals or insects as a vector of transmission, to finally continue its development or spread on your cannabis plants.


1. What exactly is Botrytis, or gray rot of cannabis plants?

2. How to avoid the appearance of Botrytis in a cannabis culture?

3. The importance of the cleanliness of the tools and the culture space 

4. Maintain insects out of reach of cannabis plants

5. How to identify Botrytis in a cannabis culture?

6. How to get rid of the Botrytis?


THE botrytis is a pathogenic fungus which is also known under the name "Gray rot", it's just a fungal disease Capable of affecting your cannabis plants anytime, although certain climatic factors promote its appearance and propagation, such as high humidity, which can be caused by autumnal torrential rains or sudden variations in outdoor temperature.

The flowering stage represents a delicate period, especially if it takes place outdoors, because our dear high quality buds could be damaged permanently at any time. Apart from climatic conditions, there are also other factors that can facilitate the potential appearance of Botrytis, such as the presence of insects Like the caterpillars near plants for example, because their defecations promote the presence and development of this cryptogamic disease.

Once the fungus has settled, it is not so easy to eliminate it. It is always preferable to avoid an attack caused by fungal diseases as powdery mildew, mildew, fusarium or alternaria On our cannabis plants. Learning to recognize and distinguish these cryptogamic diseases is a fundamental thing for any cultivators worthy of the name, because mildew and powdery mildness have similarities in terms of their characterization, yet they are very different.

It is for this reason, that it is always necessary to use quality land, taking care of the life of the soil and the health of the roots. If you see spots appearing on the leaves, it's always symptomatic of something abnormal. This can be the indicator of certain nutrient deficiencies or the evocative sign of manifest mold.

What is certain is that the damage produced by all of these plagues can be heavy with consequences, if they are not treated in time. However, we give you certain crucial advice which should allow you to dismiss Botrytis, then eliminate it permanently, while preserving the fruit of your harvest.

What exactly is Botrytis, or gray rot of cannabis plants? 

Botrytis is with the greatest certainty, one of the mushrooms that we most frequently meet during the cultivation of cannabis. Gray rot is most often developed using plant waste, like the remains of roots, stems, leaves, or even dry flowers, which litter the ground. Mycelium constitutes the vegetative apparatus of fungi, the main role of which is to promote food, is present within these plant remains.

Therefore, If the temperature increases, the fungus or mold will develop easily. This is also the reason why spring and autumn represent the two periods of the year which are conducive to the appearance of Botrytis. This is logical in fact, because precipitation is very abundant in water during these two periods, which naturally increases the risk of formation of different molds.

During the day, mycelium develops fungal structures called Conidiophores. The conidies, which are the spores which come from the latter, are arranged on the ends of the conidiophores and they are mobile in the atmosphere until reaching the leaves, the stems and the flowers to finally settle there and thus continue their development or propagation process. Botrytis spores can stay dormant (latency) for many years, without revealing symptoms, until favorable climatic conditions are ultimately met and ultimately allow their reproduction as their spread on new hosts.

How to avoid the appearance of botrytis in a cannabis culture?

It is obviously preferable to avoid any attack on the part of this fungus, by implementing certain prevention measures. The first important thing to achieve is to always keep Your cleanest possible culture space, without never allowing plant waste dragged.

Then make sure your different tools or utensils are always well disinfected, to avoid primary contamination through contact with other plants in your garden. If the cannabis plants are too close to each other, then the spread will be done by the spores, which will be fixed on a new healthy plant to continue their breeding process.

The importance of cleanliness of the tools and the culture space 

It is fundamental to always maintain perfect hygiene in the heart of your culture space, because it is the first element that will allow you to hold the botrytis of your dear favorite plants out of reach. Also make sure, always Clean all of your tools well as your culture equipment After each use using a powerful disinfectant product. We also advise to replace your clothing when you go from space to space, in order to significantly reduce any risk of contamination.

It is up to it that when you detect a part affected by the symptoms of the Botrytis on a plant, you will then have to immediately remove it, also removing preventively a few centimeters from the healthy part. This in order to eliminate and effectively isolate any new attack of this pathogenic fungus.

Maintain insects out of reach of cannabis plants

Insects constitute the second harmful scourge for our favorite plant, it is therefore necessary to maintain the latter as far as possible from our favorite activity. The pests cause the same difficulties as mushrooms, that is to say that they undermine the good future of our dear plants at each phase of evolution, whether for growth, flowering or both concerning production as well as the quality of our harvest.

All this to make you understand, that it is more difficult to eradicate them than to warn their arrival. It is also good to know that these mushrooms will contaminate new hosts more quickly who have already been weakened by insect bites. Outside, we advise to carry out wide spectrum preventive treatments during the summer period, in order to limit the presence of caterpillars during flowering for example.

How to identify Botrytis in a cannabis culture?

It is true that it is not at all easy to identify the formation or the first symptoms of this fungal disease during the first stage of its evolution in the buds. Primitive signs demonstrating an infection, are characterized by The necrosis of stems, branches and leaves. This corresponds to the period during which The coloring of the contaminated tissue becomes brown, with a damp texture, before observing the appearance of Brown circular spots on flowers, which will then evolve towards the gray, and finally see a notorious drying out of the infected part. The part concerned finally seems as dead. 

How to get rid of the Botrytis?

If you want to eliminate the botrytis from your marijuana cultures, you will have to limit the indoor humidity to the height of 60% maximum, during the last four weeks of flowering, because the Botrytis still occurs during this period. As we have already said previously, it is also necessary to remove all the affected parts of the plant, also taking a few centimeters from the healthy parts per prevention.

One important thing to achieve is to lower your air humidity to values ​​close to 50 to 60% maximum, with an ambient temperature around 26 to 27 ° C to literally dry out the interior space. In the event that the Botrytis makes a lightning attack indoors, as outside, you have to think quickly about the anticipation of the harvest, otherwise you risk losing a large part of the latter.

In the event that this fungus causes an attack at the start of flowering, you can spray as a treatment, a solution containing beneficial antagonistic fungi like Trichoderma Harzianum, Ulocladium Atrum or Gliocladium roseum on each marijuana plant. This type of treatment should quickly stop the development of this mold.

Again, the best thing remains prevention, be sure to permanently obtain values adequate climatic (temperature, humidity), and to maintain impeccable hygiene conditions. Here you have the main guarantees of the success of your harvest, whether indoors or outdoors. If you choose to carry out outdoor crops, then the first size criterion to which you must attach a major consideration, will be the choice of Varieties of high quality cannabis seeds that you are going to buy. 

It is true that mold problems usually occur at the end of summer, or to early fall When the marijuana plants endure their last weeks of outdoor flowering. The large quantities of water produced by this precipitation during a fairly long period, associated with a potential poor air circulation and therefore to a extremely high humidity in the dense heads sips of resin trichomes.

Imagine now that we cultivate hybrids or varieties with dominance indica under these conditions, so it is a dramatic situation that presents itself to us. This is the reason why the selection of varieties of your "seeds" or cannabis seeds is a fundamental aspect once again. We advise to cut your plants, and in particular all the leaves which prevent the passage of air within the structure of each marijuana plant. It is clearly a factor that can facilitate the spread of mold.

The latter can also obstruct the passage of light and thus limit the formation and weight of the heads of your harvest. In addition, as temperatures fall towards the beginning or around mid-September, and the hygrometry rate is high because of the fall rains, it is logically necessary to reduce the amount of water in the soil During watering in recent weeks, Because the evaporation phenomenon is no longer the same as during the hottest days of summer. On the other hand, this excess water in the ground could be fatal for our dear heads, because if our buds are very dense, then the risk would be increased.