Our website is intended for adults only (18+)

By using this website, you confirm that you are 18 years or older and agree with our Privacy and Cookie Policy

EUR English

Leaf Septoria – An In-Depth Guide To Yellow Spots On Cannabis Leaves

Last updated: 22 September 2023

yellow spots on leaves

There’s nothing worse than taking a routine look at your plants and spotting anything but beautiful, healthy green leaves. Discovering yellow spots or brown and black spots on leaves can be discouraging, to say the least. Luckily, it’s just a sign from the plant showing you that changes need to be made. If leaves could talk, this is how they’d do it. Leaf septoria shows up initially as yellowing leaves with brown spots. This plant disease is a fungal pathogen that can affect the growth of your marijuana plants. It’s therefore important to know how to prevent as well as effectively treat it if necessary. Here, we’ve put together an in-depth guide into leaf septoria and everything you need to know about this cannabis condition. 

What Is Yellow Leaf Spot?

leaf septoria

Yellow leaf spot, or leaf septoria, is a common disease that affects many types of foliage and plants including cannabis. When left untreated, leaf septoria can stunt the growth of the plant and negatively affect the final size and quality of the harvest.

Leaf septoria is caused by the fungus Septoria lycopersici. This fungus is known for originating on dead foliage and is often found in garden weeds, meaning the spores can be transferred quite easily to common garden equipment or found abundantly in outdoor environments. When transferred to cannabis, leaf septoria causes unnecessary stress and hinders the overall growth of the plant. 

fast flowering cannabis seeds

Tips For Identifying Leaf Septoria

brown spots on cannabis leaves

If you’re looking to avoid disappointing harvests, you’ll want to keep an eye out for the growth-deterring leaf septoria. Fortunately, it’s pretty simple to identify. If your plant is infected, you’ll find yellow leaves with brown spots on the lower areas first. The spots tend to vary in color but usually begin as uniform yellow circles. Inside the circle, there may be a raised bump, which is actually the spore of the fungus. The affected areas will transform from yellow to brown before drying out and withering to death. Once you’ve identified and confirmed that your marijuana leaves are turning yellow with brown spots, a sure sign of leaf septoria, there are a few ways to treat the disease. Let’s cover these treatment options next. 

cannabis plant symptomsREAD NOW

How To Treat Leaf Septoria

rust spots on leaves during flowering

To effectively treat leaf septoria, remember: the condition originates from spores, which makes it easy for them to travel through water, direct contact or wind. So, in addition to treating the disease with one of the methods below, you’ll want to deep clean the entire area along with any tools or materials you’ve been using. The spores are capable of hiding out in winter and re-emerging with the arrival of warmer weather, so it’s important to completely dispose of any of the plant material that’s been affected, too. 

weed growing slowREAD NOW

Here are a few methods you can use to treat yellow spots on weed leaves, aka leaf septoria. 

Remove Infected Leaves

yellow spots on cannabis leaves

As we’ve mentioned, any infected leaf is carrying a spore of the fungus. The first action you need to take when discovering yellow spots on cannabis leaves is therefore to completely remove every one you find. However, do so carefully. You won’t want the spores traveling to other plants if they’re not infected yet. At the same time, you might want to de-leaf or prune any stems to improve nutrient circulation.

potassium deficiencyREAD NOW

Improve Air Flow And Temperature And Eliminate Moisture

brown spots on marijuana leaves

Because leaf septoria thrives in hot and wet conditions, you’ll want to immediately improve your air circulation. In addition, adjust or monitor the temperature and humidity to remain at 20-25C (68-77F) and 50% respectively. Improving your airflow could be as simple as adding a fan or adding ventilation in heat-retaining rooms. De-leafing will also help, as this allows more air to circulate throughout the plant. These measures are obviously more important to implement in indoors rather than outdoor grows.

Avoid Moisture

brown spots on leaves during flowering

What adds to the spread of spores? Excess moisture. Therefore, you’ll want to take a few precautions to avoid any additional moisture pooling up or affecting plants that have leaf septoria. This includes being careful not to spray the plant leaves with water. You may even consider watering less to allow your soil to completely dry out. When you do water, be sure to do so in the morning so that the water can dry out throughout the day in full light or sun

Mediate Your Soil And Remove Weeds

yellow spots on weed leaves

If you’re growing outdoors, you’ll want to mediate your soil to ensure you’ve eradicated leaf septoria spores completely. To do so, rake the area and remove all vegetation or leaves that may have fallen from the plants and weeds in the ground. If you can, let the area dry out as much as possible. Once dry, add a layer of mulch, which will help protect the emergence of the spores again. After your harvest is complete, you may want to move your growing area completely or else replace all the soil. 

best soil for growingREAD NOW

Apply Anti-Fungal Sprays

leaf septoria cannabis

Copper-based fungicides and broad-spectrum fungicides can be effective at eliminating the spread of the leaf septoria fungus. These options can also be used as preventative measures, too. A more natural option that could help treat the spread of leaf septoria is neem oil. Be careful with the application of neem oil, however, as you won’t want it to get on your buds. It can leave an unpleasant taste and smell

How Do I Prevent Leaf Septoria?

To avoid finding yellow spots on weed leaves or preventing the spread of leaf septoria there are a few measures you can implement. First, be sure you monitor your environment for proper air circulation, temperature and humidity levels. This includes avoiding extra moisture, watering in the morning when possible, and allowing for proper drainage. Of course, keeping your plants healthy is just as important. Leaf septoria is less likely to infect healthy plants or strong genetics that are more immune to detrimental diseases. Purchasing your seeds from trusted breeders will also help you from the get-go. Lastly, begin with fresh soil that has plenty of nitrogen to get off on the right foot with the proceeding crop. Adding helpful bacterias or fungi like Bacillus Pumilis and Trichoderma to your soil is an extra supplement that can promote health and prevent disease. 

Finally Armed Against Yellow Leaf Spots

yellowing leaves with brown spots

Coming across yellow spots on leaves isn’t a good sign for any cannabis plant, but fortunately, leaf septoria is both treatable and preventable. As always, it’s important to take preventive measures and monitor your plants for proper nutrient uptake and normalcy in growth. If you’re not already doing so, make sure you’re taking a good look at your plant’s leaves regularly. Doing so can help you discover leaf septoria early and treat the condition before your crop’s end product is affected.

Oops, no comments yet. Be the first one to give your feedback!
Add a comment

How to post a comment

Thank you for leaving a comment for us!

Your feedback will be posted shortly after our moderator checks it.

Please note that we don’t publish reviews that:

  • Are written in ALL CAPS
  • Use aggressive or offensive language
  • Promote other websites (include contact details or links)