Cannabis pests and diseases

Cannabis pests and diseases

Di: Dra. Weed - Anita Bucci Coltivazione

There are many types of diseases and pests that plague plants. These organisms may attack the flowers, the foliage, stems or roots, which can negatively affect plant growth and development, causing a yield drop. Pathogens that attack the roots are located in the soil, awaiting optimal environmental conditions to spread.

On the contrary, pests that attack plant organs are found over the soil or substrate and can be transported by wind or rain, by other insects and even by ourselves. This is why you should always take a series of precautions before entering the garden or the installation where you are growing your plants. Keep in mind that we can carry anything in the sole of the shoes, clothes and even in our hair! Remember that saying: PREVENTION is better than cure!

Next you will find a description of pests and diseases that can infect our plants so you can learn how to identify them.

Bacteria / Infectious diseases

Bacteria usually affect foliar organs of plants. If we compare them with fungi or viruses we could state that bacteria cause fewer diseases. They reproduce rapidly blocking xylem and phloem tissues, which are the main organs that transport water and nutrients from the roots to different parts of the plant. We can easily identify them because when the bacteria get to colonize the plant tissue, they form angular spots on the edges of the leaf, forming a yellow ring that surrounds the dead tissue.

It is hard to find control products in the market for this type of diseases so we can prevent this from happening by providing a healthy soil and always using natural products as precaution, such as propolis for agricultural use, for example.


Fungi, as we have seen in previous articles, are important organisms but they can also harm our crop.

When these microorganisms parasitize the leaf you can observe necrotic spots. They can be identified under microscope by the spore shape and traits that differ among fungi. Spores are highly volatile but they can be also transferred through water and mechanically.


These microscopic worms can be found in the soil, directly attacking at the roots and blocking the transport of nutrients and water. The plant may look yellowed, wilted or stunted if nematodes are feeding on the roots.

Nematodes prefer high temperatures, they spread mainly through water but they can also be carried in an infested soil. This is why it’s so important to select the best quality when choosing the substrate you are going to use!


These organisms are the smallest and when they attack the plant, it can suffer from growth retardation. Some cause blisters on the leaves and a “mosaic”- like mottling and discoloration, known as mosaic burn. The dreaded hemp streak virus (HSV), or mosaic virus, causes severe damage by delaying and reducing flower production. Other insects and bugs can transmit it but the virus can also be carried by us from one area to another. Symptoms are often confused with those of nutritional deficiencies, so before using any product make sure you correctly identify the issue your plant may be experiencing.


Here is a brief list of the most common pests that usually affect cannabis plants:

 Red spider mites They can pierce the leaf down to its cells with their straw-like mouth parts and suck up the liquefied insides, since they are sucking insects. The first symptoms of infestation are tiny yellow dots on the surface of the leaves and they can propagate fast under the right temperature and humidity conditions. Always check the underside of the leaves since this is where they lay their eggs!
 Micro mites These parasites are tiny and, unfortunately, not visible to the human eye. They also lay their eggs on the underside of leaves, generating saliva with a toxic protein which can cause malformations and growth retardation to the plants.
 Aphids They perforate the leaves and feed on the fluids they contain. There are numerous species of aphids that live in colonies and can reproduce very quickly.
 Caterpillars / budworms We can easily identify this pest if you notice holes or missing pieces in the leaves. Also, you may find some tiny spots that are made by the feces of these insects.
 Thrips These tiny insects are pale-colored in their nymph stage but can still be seen. They are also sucking insects that cause lesions on the leaves that look like silver stains with an irregular shape.
 Whiteflies They are easily detectable since they behave like spiders or mites, eating essential nutrients from plants. Insect trappers, such as yellow adhesive strips, work well to fight them.
 Mealybugs Their feeding is accompanied by a production and secretion of honeydew, a sweet fluid which makes the plant sticky and encourages the growth of sooty mold fungi, attracting other insects that can transmit other diseases. 
 Leaf miner These bugs feed on the inside of leaves, creating a path-like tunneling pattern easily recognizable. This, together with the dirty trace of their deposits, may cause other diseases.
 Crickets and grasshoppers They will eat your plant in one night! Be careful and, if you see any, you already know what to do!
 Downy mildew / powdery mildew This fungal disease is extremely harmful. Infected plants display white powdery spots on the leaves and stems. In the case of downy mildew, leaves become yellowish and flecked with tiny dark stains, producing a softening of the leaf tissue.
 Fusarium This is the most feared fungal infestation by all growers because it can cause great damage to your entire cannabis crop. It originates in the root area and then expands towards the stems and leaves, reaching all parts of the plant.
 Botrytis This mold appears in places with high humidity levels and can spread rapidly.  Fungus affects leaves, forming yellowish-brown patches, but mainly attacks the already formed buds.
 Altenaria Is a fungus that lives in the soil and also requires high temperatures to develop and propagate. Leaves that are infected by alternaria display mottled dark and light green patterns in some areas. 
 Virus Hemp Streak o       mosaico  *(As described previously in the section above).

I hope you find this article useful to protect and maximize your crop yields.

Kannabia Seeds Company sells to its customers a product collection, a souvenir. We cannot and we shall not give growing advice since our product is not intended for this purpose.

Kannabia accept no responsibility for any illegal use made by third parties of information published. The cultivation of cannabis for personal consumption is an activity subject to legal restrictions that vary from state to state. We recommend consultation of the legislation in force in your country of residence to avoid participation in any illegal activity.