Stop Leaf Septoria (Yellow Leaf Spot) in Its Tracks!
Sometimes called “yellow leaf spot” or “leaf septoria,” this condition is caused by a fungus (or sometimes a bacteria) that attacks cannabis plants and usually appears in warm, wet weather. The symptoms first appear on the bottom leaves of the plant.
The spots may have darkened borders and may have a hard growth in the middle like a little pimple, but the thing that makes the spots the most unique is they are often very uniform, like little circles. Each spot is the receptacle of a spore (ewwww) which look like tiny dark specks in the center of each spot.
Although the spots often appear yellow like in the picture below, they will start turning brown over time. So if you see round brown spots on your cannabis leaves it could also be caused by leaf septoria.
Solution to Leaf Septoria
This fungus spores may stay in the soil over the winter, and attack your plants in the summer. Spores are also easily spread by wind and rain.
- Immediately (and carefully) remove all affected leaves to get rid of as many spores as possible.
- Prune any leafy parts of the plant to improve circulation through the plant
- Avoid getting water on the leaves or laying on top of each other – you want to avoid moisture
- Make sure to keep the ground under your plant clean. Rake away all leaves and vegetation. Adding mulch can also help prevent spores from spreading.
- Keep plants healthy, sicks plants are much more susceptible to leaf septoria than healthy plants
- One way to help prevent this fungus from attacking your plants is to rotate crop sites or move to a new location every year.
- A copper based fungicide or a broad spectrum fungicide may be effective at stopping the fungus from spreading though they are best used as a preventative.
- Depending on exactly what’s causing your leaf spot, Neem Oil may be used to help combat the problem. Neem Oil will leave an unpleasant taste/smell on buds when used to treat flowering plants, so don’t let this stuff get near your buds! You will need a mister (also called a “One-Hand Pressure Sprayer”) to spray all the leaves evenly, since neem oil and water can separate easily. Try spraying just a small part of the plant and see how it reacts first before spraying the whole thing.
Causes of Yellow Leaves (From Most to Least Common)
1.) PH is Too High or Low at the Roots
Whether you’re growing in soil, coco coir or in hydroponics, probably the most common reason to see yellowing and other nutrient deficiencies is the pH near the roots is too high or too low. Cannabis plants have a difficult time absorbing nutrients when the pH is off, resulting in nutrient deficiencies even if the nutrients are actually present near the roots.
- Yellow or other oddly colored leaves
- Spots, stripes or patches
- Burning around the edges of leaves
- In fact, basically any nutrient deficiency can be triggered by incorrect pH!
How Do Growers Get It?
Growers who don’t make sure their pH stays in the right range will often run into nutrient deficiencies, even if they’re starting with a pure source of water and good soil!
- Soil Optimum: 6-7 pH
- Coco / Hydro Optimum: 5.5-6.5 pH
How to Fix
- Use a kit or PH Pen to test the pH of water before you give it to your plants, and adjust if necessary by adding an acid or base to your water
- Learn How to Fix Incorrect pH
These symptoms look like nutrient deficiencies but are actually caused by incorrect pH!
Most water sources contain enough copper (which the plant needs in very small amounts) so copper deficiencies like this one are almost always caused by incorrect root pH
Another common culprit of yellow leaves from incorrect pH is a potassium deficiency. Cannabis plants love lots of potassium, especially in the flowering stage, but nearly all cannabis-friendly nutrient systems contain plenty of potassium. If you’re adding nutrients to the water, this deficiency is almost always the symptom of a pH problem.
This is also a potassium deficiency, even though it looks a little like nutrient burn (too high levels of nutrients). The main clue is the yellow striping on the leaves, which tends to get worse over time until leaves are mostly yellow. Another clue is the brown tips go in further than typical nutrient burn.
Stripes on the leaves (click for close-up) indicates that this is not a Nitrogen deficiency, even though the symptoms are similar. In this case, the symptoms were caused by the pH being way too high.
Poor Watering Practices
It’s much more common to over-water than under-water cannabis plants, and the symptoms are very similar. In either case, the solution is to learn how to water your plants exactly the right amount at the right time!
Symptoms of Poor Watering Practices
- Droopiness (it’s normal for plants to droop a little before the lights go out, but you know the drooping is a problem if it’s already happening at the beginning of their “day”).
- Odd problems and symptoms from poor water practices including yellowing and sometimes other deficiencies.
- Overwatering – leaves seem “fat” and swollen with water. Often you’ll have a feeling you may be overwatering your plant, especially if it’s a small plant in a large container.
- Underwatering – leaves often seem “papery” and thin because they don’t have any water inside them. Chronic underwatering leads to overall yellowing and deficiencies.
How Do Growers Get It?
- Overwatering is most common with young plants since they still have small, weak root systems
- You can hurt plants by giving too much or too little water at a time, and you can also cause persistent droopiness by watering too often or too infrequently
- Bad soil with poor drainage can cause the symptoms of overwatering even if you’re watering the plants perfectly!
- Small plants in big containers are easily over-watered
- Big plants in small containers are easily under-watered
- Growers who spend long periods away from their plants and/or don’t pay attention to their watering needs are much more likely to run into problems with droopiness!