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The Alternaria fungus infection can severely damage a cannabis grow, which is why it’s essential to understand the conditions that promote its spread to apply effective preventative measures.
What is Alternaria?
Alternaria is a type of microscopic fungus that, despite its tiny size, has a major impact on agriculture. It is responsible for 20% of crop losses, making it one of the most dangerous threats to plants.
However, Alternaria doesn’t just affect plants; it can also harm humans. In fact, studies estimate that it causes allergic reactions in about 15% of the population. Specifically, common symptoms include allergic rhinitis and bronchial asthma, as well as skin-related issues.
Moreover, researchers have so far identified 44 species of this fungus, which is found everywhere and plays a crucial role in the decomposition of organic matter.
Risk factors
Alternaria spores spread easily through the air, soil, and even by attaching to cuttings or seeds. If the right conditions exist for its growth, the fungus can quickly infect and destroy plants. The key factors that increase the risk of infection include:
- High humidity levels.
- Warm temperatures.
- Poor or sterile soil.
- Improper nutrient management.
- Previous nematode infections.
Life cycle of Alternaria Fungus
There are many species of Alternaria, each with unique characteristics, but they all share a similar life cycle. Besides, this fungus produces asexual conidia spores, which cause dark spots on infected leaves.
Conidia are reproductive cells carried by air currents and deposited onto plants. They usually wait for nighttime dew to germinate, at which point they penetrate the leaf tissue to feed and spread rapidly.
Symptoms
Alternaria is difficult to control because it spreads easily through air, water, and infected seeds. Furthermore, the only way to identify it is through the symptoms it causes in plants, as it is impossible to see with the naked eye. As a result, the infection is often already widespread by the time it is detected.
The main warning signs of Alternaria infection include:
Abnormal stem growth
If a plant begins developing unusually long stems, especially right after germination, it may be an early symptom of an Alternaria infection.
Dark spots on leaves
Alternaria fungus creates distinctive spots that are easy to recognize once identified. They appear as dark purple-brown patches with yellow borders, often several centimeters wide, typically forming along the leaf veins.
Wrinkled and yellowing leaves
As the infection spreads through the leaf veins, the leaves turn yellow and begin to wrinkle before eventually falling off.
Necrosis
Plants may develop necrotic areas, meaning dead tissue.
Preventing Alternaria Fungus
As we’ve discussed, the biggest challenge with Alternaria is that by the time it is identified, it may have already spread throughout the entire crop. For this reason, implementing preventative measures is crucial. Below are some key recommendations:
- Use seeds from reputable seed banks.
- Maintain a clean grow space.
- Remove dead leaves and decomposing organic matter.
- Prevent prolonged moisture on plant leaves.
- Water plants early in the morning to allow them to dry before nightfall.
- Water directly into the soil, avoiding wetting the plant.
- Ensure proper plant spacing.
- Maintain good airflow in the grow space.
- Never reuse soil from previous grows.
How to eliminate Alternaria
If your plants are already infected with Alternaria, the best solution is to use fungicides. Ideally, start with natural treatments, and if the problem persists, move on to stronger chemical options. It’s important to avoid applying chemical treatments during flowering, as the flowers absorb active molecules.
The most commonly used natural fungicides include:
Horsetail Extract
This plant contains equisetonin, a saponin that is toxic to fungi. It’s also rich in flavonoids and silicic acid, which help strengthen plant structure and reduce fungal susceptibility. Horsetail is one of the most widely used organic fungicides.
Potassium Soap
Another excellent product for preventing and treating plant pests, it eliminates fungi and insects while enhancing photosynthesis. It’s often combined with other treatments, as it helps leaves absorb solutions more effectively.
Propolis
Produced by bees to protect their hives, propolis has antibacterial and antifungal properties, making it an effective treatment for Alternaria infections. Additionally, it contains vitamins B, C, and E, which support plant health.
There are numerous products available on the market that combine natural ingredients, such as Fungi Boom or Killer Boom, as well as conventional fungicides containing trifloxystrobin, chlorothalonil, triflumizole, and other chemicals to combat highly resistant fungi. The key is to strictly follow the manufacturer’s instructions for proper application.
