- You may not yet be familiar with septoria leaf spot, a fungal disease that affects the leaves of cannabis plants. The leaves turn yellow, as if the plant were suffering from a nutrient deficiency, which can be misleading…
- This harmful disease is also known as septoria; it primarily affects the lower branches of the plant and is more common in outdoor crops.
- However, while this condition does not usually result in plant loss, septoria can significantly reduce the total yield of high-quality resinous buds, which ultimately determines the much-anticipated harvest.
- In this article, we explain in detail what Septoria is, how to identify its various symptoms on cannabis plants, what conditions contribute to its development, and, most importantly, what steps to take to eliminate it from your marijuana crop.
- What is septoria?
- What are the symptoms of septoria?
- What conditions contribute to the development of Septoria leaf spot?
- How can you control septoria in cannabis cultivation?
What is septoria?
Septoria leaf spot, also known as leaf septoria, is a fungus in the Mycosphaerellaceae family that frequently affects cannabis plants grown outdoors. It is a type of mold that most commonly occurs in climates with generally high temperatures and high humidity levels typical of that region of the world.
It is a fungal disease that can be caused by more than a thousand different pathogenic fungi. In fact, two specific strains have been clearly identified as the cause of the disease; these are fungal diseases known as Septoria cannabis and Septoria neocannabina.
What are the symptoms of septoria?
Symptoms of septoria leaf spot always first appear on the leaves of the lower branches of the plants, during the growing season or flowering. We then observe the gradual development of circular, brown necrotic spots, which are bordered by yellow lesions on the leaf surface.
These spots may appear dark and have a raised center, resembling a small pimple, but one of their distinctive features is that the vast majority of them have a fairly similar diameter. Thanks to the raised center of each spot, spores can attach to this area like a target, thereby enabling the precise development and reproduction of this fungal rot.
As time passes, the spots dry out and the leaf tissue cracks, leaving a hole resembling the impact of a bullet that has pierced the surface. This is entirely normal, as it perfectly reflects the progression of the disease: gradually, the leaf veins—which are essential for the leaves’ irrigation—become severely damaged, ultimately blocking the flow of vital resources (sap containing water and nutrients).
If the level of fungal infection is high, you will notice the leaves curling, wilting, and dying, and eventually falling to the ground. We will therefore see some defoliation of the lower parts of the cannabis plants. As mentioned above, this type of fungus first attacks the lower leaves; however, it is possible that the leaves at the top of the canopy will also be affected during flowering, and the same applies to the stems and even the cotyledons of each plant.
What conditions contribute to the development of Septoria leaf spot?
Septoria leaf spot typically appears in outdoor crops during hot summer days, particularly following heavy rainfall. Since we cannot control the duration of a rain event, if it is long and intense, it stands to reason that this significant accumulation of water will lead to high humidity in the air. Another distinct cause that could trigger the onset of this fungus is a nitrogen deficiency in the growing medium.
One must be wary of how spores behave over time, as they can remain dormant ( in a state of latency) in the soil or substrate during the winter; once conditions become more favorable in the summer, they will colonize the leaves of their new host to form a new colony, thereby maximizing the spread of these molds.
How can you control septoria in cannabis cultivation?
To eliminate septoria leaf spot from your cannabis crop, you must remove and dispose of all yellow leaves showing advanced symptoms of this fungal disease at a waste disposal facility, in order to isolate the spores as soon as possible and prevent the fungus from persisting in your crops over time. Be careful with leaves lying on the ground or growing medium, because when you water, you could spread spores onto the medium and carry them deep down to the roots.
Be sure to prune the plant’s structure and leaves to significantly improve air circulation within the plant and prevent moisture buildup, which can lead to various fungal diseases such as botrytis, downy mildew, fusarium, alternaria, powdery mildew etc. If your crop is infected with a disease such as septoria, try to maintain a constant humidity level close to 50%.
As you can see, these parasitic fungi can cause significant problems for your favorite crops, and the major issue that can arise when septoria is present is the blockage of vital nutrients to the plants, which occurs through the xylem. As we’ve already mentioned in other articles on these fungal diseases, this mold most often occurs because the plant’s immune defenses are clearly failing, which provides easy access for this type of rot.
For this very reason, it is essential to provide the right amount of water, nutrients, air, and light to prevent this problem and ensure optimal plant growth in our cannabis cultivation. Also keep in mind that this problem can lead to other related issues, as it may facilitate the presence and invasion of a multitude of insect pests.
Although treating plants with a product like neem oil is an excellent solution to this problem for all growers, it is not always a miracle cure capable of eliminating all these pests. One way or another, this will cost us time, and we may lose plants in the process—and thus part of the harvest.
This could even lead to a shortage in your bud supply for the current year, so it’s better to be safe than sorry. Also, be very careful during the flowering stage of your cannabis plants to avoid excessive humidity (above 55–60%), as this increases the risk of fungal infections like botrytis. This fungus is quite common in cannabis cultivation, which is why it could easily make an appearance soon. A stable temperature in an indoor grow setup is also crucial for preventing any mold-related issues.
Be careful when watering your plants, whether indoors or outdoors—try not to soak the entire plant too heavily (leaves, stems, buds), as a significant buildup of water or excessive moisture within the plant’s structure could lead to a high risk of fungal rot and other issues, such as the spread of spores to other parts of the plant.
Consider using a high-quality root stimulator once a week to maintain healthy, vigorous roots with optimal nutrient uptake from the soil. Rest assured, if you want to grow your own seeds, as this fungus does not directly transmit the disease to the seeds.
A good way to prevent many fungal diseases, such as Septoria, is to start by carefully selecting the highest-quality cannabis seed varieties when planning your cannabis grows. To do this, it is necessary to choose varieties that are resistant to the moisture-related issues discussed here, both during growth and especially during flowering, in order to ensure the viability of our abundant production of high-quality cannabis buds.
Using mulch is also an excellent idea when growing cannabis outdoors, as it helps prevent the spread of spores in the soil, thereby protecting it from the spread of rot. At the same time, it acts as an excellent ground insulator to counter high summer temperatures, while also limiting water evaporation.
This ultimately helps protect the soil’s microbial life by effectively limiting water stress. Rotating your crop location from year to year can also help prevent this fungus from becoming permanently established in the soil, thereby avoiding many problems for farmers at the same time.
It is important to apply at least one preventive treatment using a broad-spectrum fungicide at the end of the vegetative stage to prevent the characteristic spots caused by this fungus from appearing on your cannabis plants during flowering, and to avoid more serious problems such as losing some of the resin-rich buds from your harvest. You can also apply a treatment based on neem oil, using a fairly low dosage.
Adding or mixing beneficial fungi (antagonists) into your soil, compost, or growing medium, such as Trichoderma Harzanium for example, or beneficial bacteria such as Bacillus pumilis, is an excellent step to take to combat this fungal infection.
