Leaf Septoria and Cannabis Plants | Growers Choice Seeds

Leaf Septoria in Cannabis Plants: Prevention & Treatment

As much as we’d love to say that growing cannabis plants is effortless, that’s simply not true. You have to put a lot of care, time, and energy into your plants to ensure that they not only grow but that they grow healthily, too. Thus, you have to be aware of potential plant diseases—and this includes leaf septoria.

If you don’t know about leaf septoria in cannabis plants or how to prevent it, don’t worry: Growers Choice Seeds (GCS) is here to help. Below, we’re breaking down the ins and outs of lead septoria in cannabis plants, how to treat it, and even how to prevent it in the future.

What is Leaf Septoria?

First, let’s fully understand what leaf septoria is, particularly within the cannabis plant. If you don’t already know, leaf septoria, also known as yellow leaf spot, is a fungal disease caused by the pathogens Septoria cannabis and Septoria neocannabina characterized by yellow spots on the leaves of cannabis plants. 

This disease specifically targets cannabis plants, among others, making it a concern for both outdoor and greenhouse growers.

The fungus thrives in warm, wet conditions and is particularly prevalent in places with high humidity or during rainy seasons. Leaf septoria affects the foliage of the plant but does not typically affect the buds directly; however, it can significantly impact the overall health and yield of the plant if you don’t manage it properly.

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Signs and Symptoms of Leaf Septoria

As the nickname “yellow leaf spot” implies, one of the biggest signs of leaf septoria is yellow and brown spots on cannabis leaves. Septoria leaf spots tend to have a yellow halo or border, and they also may grow in size if the disease worsens.

Initially, the yellow spots may be small, but they can grow and merge, leading to larger areas of dead tissue (also known as necrosis). The center of the yellow spots might appear to be more necrotic or grayish, sometimes with a dark brown margin. The affected leaves may yellow and wither, and the entire leaf may die off prematurely; this tends to happen to the lower ones first.

In general, you’ll likely notice your cannabis plants appear to be much weaker than before. This reduction in leaf area compromises the plant’s ability to photosynthesize efficiently, leading to stunted growth and a potentially reduced yield. Thus, it’s important to keep an eye out for all of these symptoms of leaf septoria.

How to Treat Leaf Septoria in Cannabis

If you’ve noticed symptoms of leaf septoria in your cannabis plants, don’t panic just yet. There are several immediate actions you can take that will help treat your plants and, hopefully, bring their health back to where it needs to be. First, you’ll want to start by ​​carefully removing leaves that show signs of infection (as well as any dead leaves). Make sure to sanitize your hands and tools after handling infected material to prevent spreading the disease.

Next, you need to Increase air circulation around and within the plant canopy by pruning any dense foliage. Good air circulation helps leaves dry more quickly, and this reduces the humidity that septoria fungi thrive in.

You also want to make sure you avoid overhead watering to prevent water from splashing on the leaves, as this can spread spores. Try watering at the base of the plants early in the day so that any water that does touch leaves will have time to evaporate.

Cannabis Leaf Septoria Prevention

Along with immediate actions, there are plenty of steps you can take to prevent this from happening again in the future—or even happening in the first place. For example, make sure you avoid overcrowding your cannabis plants and space them evenly when planting. This helps leaves dry more quickly, reducing the humidity that fosters fungal growth.

Maintaining plant cleanliness will help prevent leaf septoria, too. We’d suggest regularly removing plant debris from the grow area to eliminate potential sources of fungal spores. Make sure to clean your tools and equipment with a disinfectant to prevent the spreading of the disease. You should also ensure your cannabis plants are receiving appropriate nutrients, as this can help them resist infections.

Another good way to prevent cannabis leaf septoria is by placing mulch around the base of plants to reduce soil splash, as this can carry spores onto lower leaves. Organic mulches can also promote beneficial soil organisms that compete with or predate pathogens. If you’re growing in soil that has previously hosted cannabis or other susceptible crops, rotate with non-host plants for at least a season to help break the cycle of any soil-borne diseases—including leaf septoria.

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The Impact of Leaf Septoria on Cannabis Health and Yield

As we mentioned, leaf septoria affects the leaves of the cannabis plant, not necessarily the buds. However, this doesn’t mean that your plants’ overall health and yields won’t be affected. In fact, it’s quite the opposite.

Since infected leaves lose their ability to photosynthesize efficiently, the plant’s overall capacity to produce energy for growth and flowering is reduced. This loss can stress the plant, as it struggles to absorb enough sunlight to continue its growth and development, especially during the crucial flowering stage. With reduced photosynthesis and premature leaf drop, cannabis plants can become stunted.

They may not reach their full size or develop as many branches, which can directly affect the quantity and size of the buds produced. Stressed and weakened plants may produce buds with lower cannabinoid and terpene profiles, affecting the potency, flavor, and aroma of the cannabis. For cannabis growers, especially those cultivating plants for their flowers, this can significantly reduce the harvest’s value.

Monitoring and Long-Term Management

Unfortunately, cannabis leaf septoria isn’t a one-and-done disease; instead, it’s something you have to continually look out for when growing your marijuana plants. Thus, make sure you inspect your plants regularly for any signs of disease or trouble, as this can give you the opportunity to treat the problems rapidly.

You can also consider using preventive sprays of organic fungicides like neem oil, potassium bicarbonate, or copper-based fungicides. These can be applied as a preventative measure during conditions that favor the development of septoria; however, always follow label instructions and consider the implications for cannabis plants.

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Getting the Most From Your Cannabis Plants With Growers Choice Seeds

As an online seed bank, Growers Choice specializes in providing you with premium marijuana seeds fit for practically any cannabis garden. However, we’re more than just that: we also aim to give you the resources you need to have a successful, healthy grow operation, no matter how big or small. That’s why we wanted to give you the tools you need to combat pesky problems like cannabis leaf septoria or other diseases.

Our online seed bank is full of high-quality seeds that are great for growing all throughout the country. We offer only feminized seeds (no regular seeds), both in photoperiod and autoflowering strains. You can find super popular feminized strains like Granddaddy Purple or more niche options like Charlie Sheen autoflower depending on what appeals to you most—or what best aligns with your cultivation techniques.

The next time you’re getting ready to start your cannabis garden, make sure you’re fully prepared regarding any potential diseases or complications that may arise. Then, head over to our online seed bank and pick out all the high-quality, disease-resistant seeds we have to offer.


What causes leaf septoria on cannabis plants?

Leaf septoria is caused by certain fungi that thrive in warm, wet conditions. This makes cannabis plants particularly susceptible during periods of high humidity, rainy seasons, or in environments where moisture is not adequately managed.

The disease spreads through fungal spores, which can be dispersed by wind, water, infected plant debris, or contaminated tools and equipment. Overcrowded growing conditions and poor air circulation can also easily exacerbate the spread and severity of the infection.

What treatments are available for leaf septoria on cannabis?

There are a few different treatment methods available that you can try on your plants depending on your preferences and resources. Here are some of the best routes you can take to get healthy plants again:

  • Remove Infected Leaves: Prune and destroy infected leaves to reduce the spread of spores.
  • Improve Air Circulation and Reduce Humidity: Space plants appropriately and use fans in indoor settings to improve airflow. Reducing humidity levels can be achieved through proper ventilation and by watering plants at their base to avoid wetting the leaves.
  • Sanitation: Clean and disinfect tools and equipment regularly. Remove plant debris from the growing area to minimize the risk of infection.
  • Fungicides and Biological Controls: While the use of chemical fungicides is usually limited in cannabis due to safety, there are some organic and biological options. These include copper-based fungicides, Bacillus subtilis (a beneficial bacterium), and other microbial products that can help manage fungal diseases.

Can I use neem oil to treat leaf septoria on cannabis plants?

Yes, you can use neem oil as a treatment for leaf septoria on cannabis plants, especially as a preventive measure or at the early stages of infection.

Neem oil works by disrupting the life cycle of pests and fungi, acting as a repellent, and inhibiting feeding and growth. However, it’s important to apply neem oil according to the product instructions and to test it on a small area of the plant first to ensure it doesn’t cause harm.

It is worth noting that this oil is most effective when used before the disease spreads significantly.

What are good disease-resistant strains to grow?

If you’re looking for good disease-resistant cannabis strains to grow, GCS has plenty for you to choose from. You could turn to hybrid options like Cannatonic and Critical Mass CBD, as these strains have been noted for their robust characteristics and disease-resistance nature.

Autoflowering strains, such as God’s Green Crack and Northern Lights, can also exhibit strong resistance to various stresses, including diseases, due to their ruderalis genetics.

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