Fungi are a cannabis grower’s absolute nightmare. Annoying guests that generally appear in autumn and during the rainy season, determined to ruin the whole crop. There are indeed several preventing measures to avoid the conditions that provoke the appearance of these pathogens (limited ventilation, heat, humidity…). In this post, we tell you which the most common fungi that could attack your marijuana plant are, how to prevent them and, in case they’ve already settled on your plants, how to fight them.
One of the keys to the cannabis growing process is prevention. Here's a series of measures that should be taken to prevent the appearance of any type of fungus.
How to protect your cannabis crop from fungi
- Hygiene: keeping your crop clean is paramount to avoid the appearance of fungi. Whether you're growing indoors or outdoors, you have to constantly clean the area and remove dead leaves because rotten matter can be a source of infection. Completely disinfect all the utensils you use. If cultivating indoors, give the whole area a proper cleanup between each crop.
- Temperature and humidity control: Indoors, try to keep the room well aerated, the relative humidity at a percentage lower than 50 % and the temperature below 25ºC. If you're growing outdoors instead and live in a rather humid region, choose fast-flowering genetics.
- Preventive products: there are quite a lot of organic fungicides that could help prevent the appearance of fungi.
However, despite the preventive measures, these tiny organisms sometimes seem to find a way to our beloved plants and end up colonizing them. Below you'll find some of the most common fungi that can attack our marijuana plants, as well as some tips to identify and combat them.
What is Botrytis?
This pathogenic fungus is easy to recognize because it creates a necrosis process that affects all plant tissues (leaves, buds, stalks…) giving them a dry and lifeless aspect. It is one of the worst types of fungus since it spreads very quickly and we need to act very fast if we want to stop them from destroying our crop.
How to fight Botrytis
- Prevention: monitor moisture levels.
- If the fungus has already settled, cut off the infected parts, taking off some centimeters of the healthy part as well.
- Get rid of those infected parts and disinfect the utensils you've used.
- Improve ventilation.
- Raise the temperature to 26ºC and reduce relative humidity to below 50 %.
- If your plants have already reached the last phase of the flowering, harvest ASAP.
What is powdery mildew?
Powdery mildew is one of the most common fungi attacking cannabis plants. It is also rather easy to identify because a thin layer of white dust appears on the top part of the leaves. At the beginning you'll see some small circles of dust that little by little spread and become denser.
How to fight powdery mildew
Removing all trace of powdery mildew as soon as it becomes visible is very important. Otherwise, if the fungus finds its way into the bud, the whole crop is ruined because the flowers won't be fit for consumption. Preventive products: in order to prevent the appearance of this fungus, you can use organic products such as horsetail and propolis. You can also use an antagonistic fungus called Trichoderma harzianum which is to be injected in the substrate we're gonna use for growing our cannabis plants. However, if powdery mildew has already settled on your plants…
- Spray water with high levels of pH (8- 8.5). Reapply every 3-4 days.
- Spray a water/milk mix (90% water and 10% milk).
- Spray a mix of water/hydrogen peroxide (a bit).
What is Damping Off?
This disease can be caused by several types of fungi, both seed-borne and soil-borne. It is basically a rotting process that affects seeds and seedlings. This process starts when the environmental conditions are not adequate, particularly due to high humidity levels and poor ventilation. The damping-off is very easy to identify because it tends to decompose the lowest part of the stem until the seedling is unable to support itself and dies. Everything happens very fast, usually, overnight.
How to fight Damping-off
There's nothing we can do once it hits the plants because, as mentioned earlier, it moves very fast and is lethal, and, above all, it attacks plants when they're the most vulnerable. However, what we can do and we MUST do as soon as possible is remove all infected seedlings to prevent the diseases from spreading. We can also prevent its appearance by applying Pythium oligandrum (a parasite that feeds on certain fungi) and by using a sterile soil.