The root system is one of the most sensitive and important aspects of cannabis plants. Some of the diseases most dreaded by growers originate underground and can wreak havoc on cannabis crops.

Here are some strategies and tips to avoid these issues.

What is root rot in cannabis cultivation?

Healthy roots in cannabis plants are a guarantee of a successful harvest. However, there are some diseases that develop underground and can attack this specific part of the plant. In addition, certain habits must also be avoided to maintain strong and healthy roots.

“Root rot” refers to infections that affect the roots of cannabis plants. These destroy the absorbent capillaries and prevent the plants from taking up oxygen and nutrients from the soil.

Root rot can be caused by several reasons. It can originate from a poor quality substrate, from dormant fungi or bacteria in the soil like Pythium or Fusarium, or from a poor irrigation regime.

What causes root rot in cannabis plants?

The most common causes are phytopathogenic agents such as bacteria (Agrobacterium, Burkholderia, Clavibacter, etc); nematodes (Tylenchulus, Pratylenchus, Heterodera, etc); or microscopic fungi present in the upper soil layers (such as Fusarium, Pythium, and Rhizoctonia), which are highly abundant in any type of soil.

• Poor soil structure: Soil or substrate layers tend to become compacted under their own weight. This can affect the roots, creating pressure and hindering the plant’s respiration. To prevent this, vermiculite, perlite, or other substrates can be added to improve soil aeration and prevent compaction. These can also help improve the drainage of excess water.
• Poor drainage: If the soil has a poor structure, excess water from watering can accumulate, potentially waterlogging the roots and causing rot. Again, a well-structured soil drains better and avoids these problems. It’s important to remember that excess irrigation should be avoided at all costs.
• Over-watering: The frequency of watering should be just right according to the plant’s needs. If the correct level is exceeded, the soil may overflow and the drains may become clogged, leading to waterlogging issues.
• High temperatures: Fungi are present in the soil. The health of the roots, along with their genetic resistance, allows plants to naturally cope with these bacteria and microorganisms. However, these diseases are more prevalent if the soil temperature rises too high (+24ºC). Heatwaves should be avoided as they can harm not only the roots but the entire plant.

How to identify root rot in cannabis grows?

Cannabis plants give us clues about their health through the parts that we see every day, such as branches and leaves. They also show what’s happening to their roots through these channels. When things aren’t going well below the substrate, you’ll see a series of very obvious and easy-to-identify symptoms on the surface.

• Wilted appearance: Root rot deprives plants of oxygen. As a result, they lose tension: branches become weak, and leaves hang and curl up, developing spots and turning yellow before becoming brown. When growers spot this widespread wilting, they sometimes think that the plants lack water, so they increase the dose. But this can actually worsen the problem, so it’s important to pay attention to the other symptoms as well.
• Darkened roots: Healthy cannabis roots are generally white and shiny. When root rot occurs, they turn brown, or even black if the rot is advanced. This advanced stage is easily recognizable by the color of the roots, their viscosity, and the presence of a bad odor. And this can even lead to the death of the plant.
• Stunted growth: The plant slows down its growth gradually until it stops, as it finds it extremely difficult to access all the essential nutrients.
• Pest infestations: The plant’s immune system weakens, allowing other issues like insect infestations to occur.

How to prevent root rot in cannabis plants?

Curing and eradicating some of these infections that cause root rot in cannabis plants can be very difficult and costly. Therefore, implementing good prevention practices is the best solution to avoid this issue and maintain strong and healthy roots.

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• Proper irrigation practices: This is the most effective and easiest factor to control. A correct watering schedule can avoid most root problems. It’s very important not to water in excess or to waterlog the substrate for too many days. Provide a good amount of water (considering the plant’s growth phase and genetics) at the right frequency (let the soil dry before watering again); and ensure proper drainage. It’s also best not to water with warm water or during the hottest hours of the day.
• Proper drainage: To ensure good drainage during the watering of your cannabis plants, it is advisable to use pots with good drainage holes; as well as perlite, vermiculite, expanded clay, or other systems that improve both soil aeration and drainage.
• Correct temperature: The temperature of your grow is a determining factor for the activation of microorganisms (especially with temperatures above 24ºC). For example, Fusarium appears when the soil reaches between 24ºC and 30ºC. Good ventilation and a cooling system are both essential to avoid all kinds of problems.
• Be cautious when reusing substrate: Leftover or reused substrate might be attractive to reduce costs, but it needs several checks and processes so that it can be used safely. These include pasteurization and the addition of new nutrients and microbial life (such as enzymes, Mycorrhizae, Trichoderma, etc). Remove and dispose of plant debris from your grow and its surroundings to avoid infecting plants in the next growth cycle.
• Maintain hygiene and sterilize: If you’re reusing pots or other tools, it is essential to keep them clean and disinfected, especially when you’re dealing with newly germinated seedlings.
• Avoid over-fertilization: Overdosing or using the wrong nutrient combination can also cause the appearance of substrate fungi that can lead to root rot. Again, Fusarium can emerge in soils that exhibit high potassium and low nitrogen levels.
• Emergency transplant: If it’s clear that the cause of root rot is overwatering (and it’s a severe case), an emergency transplant can be performed, relocating the affected plant to a dry substrate that can absorb the excess water from the root ball. You can also use a root stimulator in the following watering sessions to facilitate the growth of new roots and help the plant overcome stress.

What products should you use to prevent root rot in cannabis cultivation?

There’s a wide range of fertilizers and root system enhancers that facilitate active prevention, meaning their use ensures that the roots grow strong and healthy, and protects them from potential threats like harmful fungi and bacteria.

• GHE Bioponic Mix: An organic supplement, based on beneficial microorganisms such as Mycorrhizae and Trichoderma, that improves soil health and strengthens the roots. It helps boost the plant’s immune system and has a preventive action against harmful fungi in the root mass.
• Prot-Eco Phytoprot Max: A natural treatment against soil fungi and bacteria. It has prebiotic properties to stimulate microbial life, fostering the creation and synthesis of the plant’s natural defenses. This benefits the root system and prevents the appearance of pathogenic fungi like Phytophtora, Pythium, Fusarium, etc.

• Prot-Eco Bio 16 Trifag: A biofungicide that’s effective against a wide range of soil pathogens. Its preventive action against harmful fungi increases root development and improves manganese absorption.
• BioBizz Microbes: A mix of beneficial microbes (including Trichoderma and Mycorrhizae) that enhances soil health and protects the roots. This product promotes the creation of plant hormones, increasing the beneficial activity and effect of microorganisms, thanks to the addition of Trichoderma.

Cell strengthening with silica

Silica thickens the cell walls of cannabis plants, leading to roots that are more resistant to drought and fungal attacks.

• Grotek Pro-Silicate: It increases the plants’ resistance to environmental stress and diseases. With its high silica content, this product strengthens the cell walls and protects plants against soil pathogens. It also provides higher resistance to water stress and strengthens the plants’ natural shields.
• Atami B’Cuzz Silic Boost: It improves cell structure and overall resilience. This is an extra boost of silica that provides greater resistance against both biotic stress (pests, fungi, and diseases) and abiotic stress (climatic, water scarcity, etc).
• Silica Power BAC: A silica additive that strengthens the cell walls. An effective prevention method against parasites and rot, which increases natural resistance to adverse conditions and improves nutrient absorption by avoiding “nutrient lockout.”

What to do when root rot appears in your cannabis plants?

The most challenging aspect is tackling a fungal infection once it’s appeared. Action must be taken quickly, with the help of authorized sources and safe and effective products.

Systemic Products

Systemic products are phytosanitary products that penetrate the plant tissue and then spread out throughout the entire plant. This way, the plant becomes poisonous for pests or infections, even if the application doesn’t cover the entire surface or doesn’t fall directly on the insects.

They’re usually more toxic than regular products, so it’s vital to comply with application times and flush the roots if needed to remove impurities and product residue.

• Lexor 25 Probelte: An effective systemic fungicide for the treatment of fungal diseases in the roots. This product includes preventive, curative, and eradicative actions. It affects the synthesis of the cell membrane of fungi and destroys it. It also prevents the subcutaneous development of fungal mycelium, slowing the development of the symptoms of infection. It reduces the infestation’s virulence and exhibits antisporulant action, meaning the fungi can’t release spores and reproduce, which halts their spread.

Application and Dosage

• Follow the manufacturer’s instructions for proper dosage and application.
• Regularly monitor the plants after treatment to ensure effectiveness.

Conclusion

Root rot in cannabis plants can be a major headache, but it can be prevented by keeping certain factors in mind and using the best products so the plants can develop a strong defensive system and strong and healthy roots.