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Disease Guide – Leaf Septoria

Yellow Leaf Spot and Cannabis Plants

Marijuana growers must be aware of diseases that can affect their plants and possibly decimate their crops. Cannabis plants are susceptible to a range of unique diseases that can do great harm, from . A good example of a disease every grower must be aware of is yellow leaf spot or leaf septoria.

These fungal pathogens are the result of Septoria neocannabina and S. cannabis, two fungal pathogens that specifically attack marijuana plants. Yellow leaf spot is more common when the weather is warm and wet, and it typically targets marijuana plants grown outdoors. However, cannabis plants that are nitrogen deficient may also suffer from this disease. What does leaf septoria look like, and how should it be treated?

What Does Leaf Septoria Look Like?

First, we recommend that you examine the lower leaves of the plant to see if leaf septoria is an issue. What you are searching for are spots that initially look like small circular lesions. The spots may be white, grayish brown, yellow, or a shade of these colors and typically appear during the flowering stage. Once the problem begins to spread, what appears to be a bump will show up on the leaf, and this bump gets larger as the disease spreads.

Yellow leaf spot primarily damages plant leaves and can sometimes harm the stem as well. While the crop won’t die off completely, the yield will be greatly reduced. The leaves that have been impacted by the leaf septoria become dry at the site where the bump appears. With time, this dry spot will break away, leaving a hole where the fungal pathogen first appeared. The cannabis flowers (buds) themselves aren’t generally affected, but the overall quantity that the grower will harvest will be much lower. The key to minimizing the harm of yellow leaf spot is to catch the problem early and take steps to resolve the issue.

Signs of Leaf Septoria on Cannabis Plants

Cannabis plants show many of the same symptoms when they are infected with yellow leaf spot. These spots often have a darkened border, and every spot on the leaf serves as a receptacle of a spore. Small bumps that resemble pimples are an indication the crop needs attention, and dry leaves that are falling are also a sign of leaf septoria.

Curing Leaf Septoria Once It Appears

The leaves most damaged by the disease turn yellow, dry out completely, and fall off the plant. Be sure to remove these leaves immediately. If they are left over the winter, they serve as a landing spot for spores. This allows them to remain in hiding until the weather turns warm. When it does, they attack the crop and cause damage. The spores are able to travel by water or wind. When they pass something, they are able to cling to it and gain a foothold.

This works when only the lower leaves are affected. In the event the yellow leaf spot has made it up to the flowers, it’s best to leave the foliage in place. When the foliage is removed from the flowering area, the plant is significantly weakened and the quality of the buds is reduced. In other words, it is better to maintain some slightly “sick” leaves than have no leaves left at all from excessive cannabis pruning.

How can yellow leaf spot be prevented?

Soil Preparation

A simple, but wise move is to rotate your crop after every harvest. This means a new location must be selected for the crop. This gives your canibus seeds fresh, balanced, pest-free soil to flourish in.  When this is not possible, remove all leftovers from the current crop, and once they have been removed, till the soil multiple times to make certain nothing remains. This will help to keep yellow leaf spot at bay.

When the soil has been properly tilled, obtain sterilized compost and mix it thoroughly into the soil. This ensures the new crop has plenty of nitrogen to allow it to get off to a good start. If sterilized compost isn’t easily available, make use of fish meal, blood meal, or soybean meal to improve the soil before planting the next crop. By doing so, you can ensure the next crop of bruce banner marijuana seeds plants will have the nitrogen they need to thrive!

Preventing Weeds

Mulch can be of help in preventing spores making their way from the ground to the plant.  Be sure to remove the dead foliage and till the ground, as explained above. Make certain the soil is completely dry before applying a thick mulch layer. Once the mulch is in place, water the plants.

Don’t allow weeds to grow in and around the cannabis plants. Horse nettle and nightshade are both good hosts for the Septoria lycopersici spores. Remain vigilant and remove these weeds as soon as they appear so the fungus won’t have anywhere to hide.

Moisture, Temperature, and Air Circulation

Control moisture when growing marijuana. Cannabis plants should only be watered in the early morning or early evening. The leaves shouldn’t be watered. Focus your efforts on the soil. This helps to ensure the sunlight doesn’t harm the leaves. If any signs of yellow leaf spot are seen, remove the affected leaves and remove them far from the remaining plants. Leaving the leaves in the growing area puts your crop at risk of future problems. The fungal pathogens easily cling to things and travel from place to place.

Indoor growers need to take care. Temperature and humidity conditions play a major role in the success or failure of a crop. Monitor these conditions and make the necessary changes immediately to prevent problems from arising.

Maintain adequate air circulation in the growing area. Install an additional fan in the indoor growing area and design the layout to create extra space between the plants. Cannabis plants grown outdoors must be regularly pruned to allow for airflow. Bushy areas of a plant need to be trimmed and leaves should not touch or lay on top of one another. Another way to increase airflow when growing cannabis plants outdoors is to elevate the plants. This allows more wind to reach each plant. When all else fails, run an electric fan outdoors to help increase airflow around the plants.

Yellow Spot Leaf Treatments

If you remain concerned about yellow leaf spot, don’t hesitate to add a fungicide to the soil before putting in seeds or seedlings. Many natural solutions are available or a grower can choose to make their own. A broad-spectrum fungicide or disease control spray is often enough to eradicate the disease. Certain growers choose to try a copper-based fungicide. Regardless of which product is used, follow the instructions on the package exactly and avoid getting the fungicides or disease control spray on the buds.

Helpful bacteria and good fungi may also be added to the soil when compost isn’t available. Two options available today are Trichoderma and Bacillus Pumilus.

Some growers choose to make use of essential oils to keep disease at bay. Many growers recommend neem oil as it treats a range of garden diseases and pests. However, remember these oils have strong scents. Therefore, they should never be applied near the buds to ensure they don’t contaminate the flavor or aroma. Compost tea may be used to mist the soil or baking soda can be added, as both help to keep leaf septoria spores away.

Compare Seed Providers

Choose a supplier wisely. Those plants with strong genetics tend to be healthier and more protected against diseases and pets. For this reason, all seeds should be obtained from one of the reputable marijuana seed banks in US. Furthermore, if leaf septoria continues to be a problem, ask the supplier for recommendations on preventing this common problem or on which strain to buy to minimize the risk of it.


Finally, cleanliness is of great importance when growing cannabis. Clean the space regularly, as this helps to spot small problems before they become major issues. This is the most important thing to remember when growing marijuana for great results. Indoor growers especially need to make certain their grow area remains clean at all times.

One mistake growers make is they fail to clean and disinfect their tools after dealing with a yellow spot leaf problem. The tools must be cleaned and disinfected with peroxide or rubbing alcohol to remove any pathogens that are present on them. This is true of every tool used, so be sure nothing is overlooked when you clean supplies. In the event the problem returns after treatment, the tools used may be the problem if they haven’t been properly cleaned.

While leaf septoria won’t decimate a cannabis crop, it can do harm. Lower yields are commonly seen with crops, which no grower desires. By remaining vigilant, you can catch this problem early and take steps to prevent additional damage. However, prevention remains the best way to combat yellow leaf spot and numerous other diseases seen with marijuana crops. If you find you still struggle with this disease after following all recommendations, the problem may lie in your cannabis strain. Genetics do play a role in how a strain withstands various diseases so keep this in mind when determining which strain to grow and which provider to buy from. Research before you buy, and you’ll save time and money in the long run. I49 seed bank has your back with our germination guarantee as long as you follow our simple guide!


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