Cannabis Plant Diseases: Recognition and Treatment


Cannabis is a flowering plant that has been cultivated for millennia for its use in textiles, medicine, and as a psychoactive substance. As with any crop, cannabis is subject to a variety of diseases that can damage or destroy individual plants or entire crops. The study and practice of identifying, managing, and treating cannabis plant diseases form a significant portion of overall cannabis horticulture. Understanding these diseases, their symptoms, and possible treatments are crucial for growers aiming to cultivate healthy, high-quality cannabis plants.

Common Diseases of the Cannabis Plant

A range of diseases can afflict the cannabis plant. They fall into four main categories: fungal, bacterial, viral, and nutrient disorders.

Fungal Diseases

Fungal diseases are arguably the most common diseases to afflict cannabis plants. Two common fungal diseases are powdery mildew and botrytis, also known as bud rot.

  1. Powdery Mildew: This fungus manifests as white, powdery spots on the leaves and stems of the cannabis plant. Left untreated, it can spread rapidly and damage the plant’s ability to photosynthesize, leading to stunted growth and diminished yield.
  2. Botrytis (Bud Rot): Bud rot is a particularly devastating fungal disease that affects the flowering buds of the cannabis plant. It causes the buds to rot from the inside out, turning them brown and leaving a slimy residue. Botrytis is more common in humid environments and can spread rapidly if not treated promptly.

Bacterial Diseases

Bacterial diseases are less common in cannabis but can still cause significant damage. Two examples are bacterial wilt and leaf septoria.

  1. Bacterial Wilt: This is a soil-borne disease caused by bacteria that attack the plant’s vascular system, blocking water transportation and causing the plant to wilt and eventually die. Infected plants often exhibit wilted, yellow leaves, and a dark, shriveled stem.
  2. Leaf Septoria: Also known as yellow leaf spot, leaf septoria appears as small, yellow spots on the lower leaves of the plant. Over time, these spots may turn brown with a yellow halo, and the leaves may become necrotic and fall off.

Viral Diseases

Viral diseases in cannabis are relatively rare and poorly understood. The most commonly reported viral disease is cannabis cryptic virus, which tends to be asymptomatic but may be associated with slower growth rates and lower yields.

Nutrient Disorders

Nutrient disorders are not diseases in the traditional sense, but they can cause symptoms similar to those of many diseases. Common nutrient disorders include nitrogen deficiency, which causes yellowing leaves, and phosphorus deficiency, which results in dark, bluish-green leaves with a purplish hue.

Diagnosing Cannabis Diseases

Correctly diagnosing a cannabis disease is the first step towards effective treatment. Diagnosis can be challenging, as many diseases have similar symptoms. However, paying close attention to the specific features of the symptoms and considering the plant’s growing conditions can provide vital clues. For example, powdery mildew is likely if a plant has white, powdery spots and is grown in a location with poor air circulation. In contrast, bacterial wilt might be the culprit if a plant suddenly wilts and is grown in heavy, poorly drained soil.

Moreover, diagnostic laboratory services can identify the causal pathogens or nutrient levels in plant tissue samples, but these are often unavailable or impractical for small-scale growers.

Treatment and Prevention of Cannabis Diseases

Once a disease has been diagnosed, the appropriate treatment must be applied. For fungal diseases like powdery mildew and botrytis, fungicides are generally effective. Many growers prefer organic fungicides such as those containing Bacillus subtilis or potassium bicarbonate, but synthetic fungicides may be required for severe infections.

Bacterial diseases are more challenging to treat, as few bactericides are safe and effective for use on cannabis. In many cases, the best strategy is to remove and destroy infected plants to prevent the spread of the disease.

Viral diseases, unfortunately, have no known treatments as of this writing. Infected plants should be removed and destroyed to prevent the spread of the virus.

Nutrient disorders are usually straightforward to treat once correctly diagnosed. The affected plant will typically recover once the missing nutrients are supplied, although it may take some time for symptoms to resolve.

Prevention is always better than cure, especially with cannabis diseases. Good preventative measures include using clean, well-drained soil; ensuring adequate air circulation; monitoring and adjusting nutrient levels; and regularly inspecting plants for early signs of disease.


While the diseases that can affect cannabis plants are numerous and diverse, understanding their symptoms, causes, and treatments is crucial for any successful cannabis grower. With careful observation, accurate diagnosis, and appropriate treatment and preventative measures, most cannabis diseases can be effectively managed to protect and even enhance the yield and quality of this versatile crop.