Culture & Grow

Botrytis: how to prevent, identify and eradicate this gray mold in your plants

Here are some techniques that can effectively prevent or destroy it

Le Botrytis cinerea is a species of necrotrophic fungi in the family Sclerotiniaceae, from the Ascomycota division. Also known as gray mold, botrytis is a fungus that can attack your cannabis plants. As difficult to fight as it may seem, there are certain techniques that can prevent or destroy it effectively. This fungus loves warm, humid environments and uses other animals, such as caterpillars, to move around and reach cannabis plants. It is also extremely contagious. If you discover infected plants, separate them from the rest as soon as possible to avoid further damage.


Botrytis is a parasitic fungus that can attack your cannabis plants at any time. It is important to know that certain conditions favor its proliferation and development: high humidity, sudden changes in temperature or heavy rain.

Everyone knows that the flowering phase is the most delicate moment because plants infected at this stage can suffer irreparable damage. Besides the weather, there are other things that can greatly increase the likelihood that your plants will be affected by botrytis mold, such as caterpillars (their droppings can be a possible source of infection). Although the botrytis fungus is particularly difficult to control, knowing how to act preventively or how to react when it is already installed could help you kill it for good.

Botrytis or gray mold is one of the most common fungi in cannabis plants. It normally develops in dead plant matter on the ground. The spawn is the vegetative part of the fungus which is found in plant debris and which allows the absorption of nutrients. It is on these debris that the fungus can easily develop when the temperature and humidity increase, making late spring the ideal time for its appearance, although it can also appear in the fall. due to increased precipitation

In broad daylight, the vegetative mycelia begin to produce conidiophores with clusters of conidia which are then released and transported by air currents until they reach the stems and leaves. The conidia of Botrytis cinerea are asexually produced spores that can remain alive for years until conditions are favorable for their new development.

Here is a glimpse of an industrial hemp plant suffering from Botrytis blight

How to prevent

The best way to control this fungus is to prevent it. It is essential to keep your culture clean to avoid the appearance of botrytis (this includes all the elements that come into contact with your plants). If the infection has already set in, you can prevent it from spreading by making sure that the healthy plants are not in contact with the plants that you think are infected. Their proximity facilitates infection by air: if a spore settles on your plants, it is very likely that they will end up being infected.

Keep your cannabis culture clean, including your tools

Ensuring that the area where you grow your plants is 100% clean is the best way to prevent the attack of the dreaded gray mold. The tools you use must be properly sterilized, including scissors, stakes, labels, etc. Also, wear latex gloves when handling the plants and try not to rub them with clothing that has been worn in other areas. You should avoid touching the buds because the fungus can be transported by air but also with your hands. Remember to carefully remove the infected parts.

Keep the tracks away

It is very important to keep insects at a distance, especially the caterpillars, because the cuticles of plants can be damaged by their bites, which facilitates the entry of the fungus inside. Take preventive measures during the summer to prevent this from happening. Thus, you will limit their presence during flowering.

A major problem for cannabis growers is to identify the infection at an early stage since the buds do not seem to be affected. One of the most obvious indicators is necrosis on the stems, leaves and branches, which makes the tissue brown and damp. Another symptom indicating the presence of botrytis is the appearance of lighter circles on the buds, with a dark brown ring around them.

How to eradicate it

If you suspect that gray mold has already settled on your plants, the best solution is to immediately remove all affected parts. To do this, be sure to always use sterilized tools. If you decide to get rid of certain buds, it is also best to cut at least three centimeters below. Then destroy all the infected areas.

How to fight botrytis indoors

If you are growing indoors, ensure good air circulation and closely monitor the irrigation schedule. This will ensure that the humidity remains low, which is essential for the well-being of the leaves and flowers. Never let the humidity level exceed 50%.

But do not think that the dangers will be over after harvest, because your flowers will still be in danger for a long time. During the drying phase, it is essential to maintain a humidity level below 60% and to ensure that the place is well ventilated. The best way to do this is to install a small extractor equipped with a charcoal filter that maintains proper air and humidity levels.

How to fight botrytis outdoors

Two things make outdoor crops more susceptible to botrytis attack: precipitation and the fact that plants can develop a very dense canopy. In summer, when the plants are still growing and the flowers have not reached maturity, it is unlikely that they will be attacked by this fungus. However, it is during late stages of flowering, in late summer or early fall, that the weather begins to change and the rain becomes more frequent, resulting in poor circulation and excessively high humidity levels.

Pruning is also highly recommended because botrytis mold likes dense, bushy plants. Likewise, one can look for a method of cultivation which allows to leave larger spaces between the plants and teaches them to grow so that they do not become too thick.

What to do with infected plants

If the preventive action does not work, you can always use Neem oil, a very useful antifungal solution to fight against infections caused by mildew, powdery mildew, botrytis, etc. Plant protection products are also very effective. The market is full of options; just choose the one that best meets your needs. You should be fully aware of the risks of this infectious fungus and decide on the products and intensity of treatment accordingly.

It is also crucial to alternate different products so that the fungi do not get used to it and therefore become more resistant instead of dying. If the problem persists, try to repeat the treatment every week, increasing the frequency if you consider it necessary.

In any event, infected buds should not be eaten under any circumstances as they can cause lung problems and, moreover, the taste of moldy grass is quite unpleasant and leaves something to be desired.

Tags : Agriculture / GrowChampignonHempmoldPreventionTechnology

The author weedmaster

Media broadcaster and communications manager specializing in legal cannabis. Do you know what they say? knowledge is power. Understand the science behind cannabis medicine, while staying up to date with the latest health related research, treatments and products. Stay up to date with the latest news and ideas on legalization, laws, political movements. Discover tips, tricks and how-to guides from the most seasoned growers on the planet as well as the latest research and findings from the scientific community on the medical qualities of cannabis.