Leaf Septoria (Yellow Leaf Spot) On Cannabis Plants

Leaf septoria is a harsh plant disease that regularly affects the foliage of a variety of plants, including cannabis.

If not handled properly, leaf septoria can be devastating to plants, destroying foliage, stunting their growth, and ultimately affecting the size and quality of their yields.

In this article we take a close look at cannabis leaf septoria, what it is, and how to treat/prevent this disease from affecting your cannabis crops.

What is Leaf Septoria?

Leaf septoria, also known as septoria leaf spot or yellow leaf spot, is a plant disease caused by a specific kind of fungus known as Septoria lycopersici.

This fungus usually overwinters on dead foliage or common garden weeds. Fungus spores can also spread onto equipment like garden stakes and netting, before germinating when conditions are right.

Leaf septoria can be an extremely damaging disease, greatly affecting the foliage and growth of a variety of plants, including tomatoes, parsley, and obviously cannabis.

As the name suggests, leaf septoria is characterized by yellow and brown spots forming on both the upper and lower sides of leaves. The spots tend to be circular with dark brown margins and tan or greyish centers. They usually measure between 1.5 to 6.5mm.

Leaf septoria usually affects plants just after they enter the flowering stage and usually forms on lower leaves first. As the disease develops it spreads its way upwards, quickly affecting multiple leaves all across the plant.

Affected leaves will usually turn slightly yellow, then brown, and eventually wither completely. Leaf septoria rarely spreads on to fruit, so it generally won’t affect cannabis flowers.

If left uncontrolled, the disease can destroy a lot of foliage. This ultimately creates a lot of stress for plants and stunts their growth as well as the size of their harvests. Leaf septoria is particularly prevalent in areas affected by extended periods of wet, humid conditions.

How to Treat Leaf Septoria in Cannabis Plants

As with most garden pests and disease, early detection is extremely important when dealing with leaf septoria. Make sure to pay close attention to your plants during extended periods of hot and humid weather, as well as during the early stages of the flowering cycle.

Once you’ve identified the disease, make sure you follow the following steps to control it and stop it from spreading:

1. Remove Infected Foliage

The first step to effectively dealing with leaf septoria is removing infected leaves. If caught early, you can usually prevent the spread of the disease by simply removing all infected lower leaves and burning/destroying them.

However, if the disease has spread to the height of your flowers, you’ll generally want to skip this step. Removing foliage from flowering areas will greatly weaken a plant and reduce the quality of its buds.

2. Improve Air Circulation

Proper air circulation is extremely important for cannabis plants and plays a big role in the management of pests/diseases.

If you’re growing indoors, improving air circulation can be as simple as adding an extra fan into your room and creating some space between your plants. If you’re working outdoors, however, this might be a bit more difficult.

Pruning is also a great way to help create airflow in and among plants. Try trimming down extremely bushy areas of your plants and avoid having leaves touching or laying on top of each other.

If you’re working outdoors, you may want to try elevating your plants slightly so that they catch a bit more wind. Alternatively, also consider running an electric fan on outdoor plants if possible.

3. Avoid Moisture

Moisture is another major player in the spread and germination of fungal spores. Hence, you’ll want to avoid moisture as much as possible.

Avoid overhead watering as this will wet the leaves of your plants and consider watering slightly less regularly in order to give the soil a chance to really dry out. Also water early in the day to allow the soil to dry out during daylight hours.

4. Mulch

Fungal spores often spread into soils where they hang out over the winter until conditions are right for germination.

While you won’t be able to change your growing medium mid-grow, there are some steps you can take to avoid any spores from the ground spreading onto your plants further.

Start by removing any dead foliage and raking the soil to remove any possibly infected vegetation. Next, dry out your soil properly. Finally, apply a thick layer of mulch to the top of your soil then water your plants.

This will help stop the spread of fungal spores from the soil up onto your plants.

5. Remove Weeds

Night shade and horsenettle are common hosts of Septoria lycopersici spores. Hence, make sure you run through your garden and remove any weeds that could possibly host the fungus.

6. Keep Track of Temperature and Humidity

Remember that leaf septoria naturally strikes in hot, wet conditions. Hence, if you’re dealing with an infection, try driving down the humidity and temperature levels in your grow space (where possible).

7. Apply Fungicides or Natural Oils

If you’re dealing with a minor case of leaf septoria, steps 1-6 might be enough to kill the disease and stop it from spreading any further. However, if you’re dealing with a more serious infection you may need to rely on some heavy-handed fungicides.

Broad spectrum fungicides and disease control sprays will usually do the trick. For extra protection, try opting for a copper-based fungicide. Either way, remember to carefully follow the package instructions when using any kind of disease control agent, and avoid getting any of it on your buds.

If you’re after a more natural alternative, we suggest turning to essential or horticultural oils like neem. Neem oil is commonly used to treat all kinds of garden pests and diseases and can easily be applied to your plants using a mister.

Alternatively, consider trying eucalyptus, rosemary, lemon, and cinnamon oils. Either way, remember that these oils have strong aromas and should never go near your buds to avoid contaminating their aroma/flavour.

How to Prevent Leaf Septoria

When it comes to gardening, it is always best to prevent diseases and pests rather than treating them. Hence, follow these tips to prevent a leaf septoria infection in the future:

💼 Rotate your plants: Avoid growing your plants in the same area and grow medium next year. Fungal spores are very good at surviving and may come back to attack your crops again if you grow them in the same areas.
🧹 Regularly clean your grow space, especially when growing indoors.
✨ Create and maintain a good environment: If you’re growing indoors, make sure your grow space is at the right temperature and humidity levels. Also, remember to make sure your plants receive plenty of airflow.
✂️ Prune regularly.

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