12 Cannabis Diseases and Problems to Watch Out For

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No matter what plants you grow, you will inevitably have to deal with botanical diseases. As you can imagine, cannabis is no exception. Whether you are growing these plants for profit or medicine, you will undoubtedly know about at least some of the diseases of the cannabis listed below.

Hopefully knowing what to look for can help you identify (and potentially treat) them early.

1. Damping-off disease

This can happen to almost any plant, but is more frequent with the cannabis plant. Pythium is a pathogen that thrives in cool, moist soil. It attacks young plants and causes their stems to rot so that they cannot take up any nutrients.

If your seedlings aren’t growing, or if they’re dropping weakly, check their stems below soil level. Look for brown stems that are thinner near the roots than above. This is a sure sign that you are dealing with Pythium.

You cannot save these seedlings, but you can treat the soil and prevent this from happening in the next batch. Use hot garlic water as a fungicide and allow the soil to dry out completely before applying the next batch. Then, use only warm water to moisten the soil. And always, always clean your tools in between uses.

2. Fusarium Wilt

Fusarium wilt is another soil-borne pathogen that tends to overwhelm cannabis plants. It nests in the xylem of the stems, so that they are not able to transfer nutrients through their sap.

As a result, the leaves will curl and wilt, and the stems will become weak. Before you know it, they will be wandering around and dying. At this point, you can simply burn the plants and treat the soil with a fungicide. Then do not plant any cannabis or nightshade plant in that soil for at least three years.

3. Downy Mildew

Humid weather, regardless of cold or hot seasonal temperatures, can cause many different fungal issues. Check the undersides of your plants’ leaves regularly and look for a gray or white fuzz. You may also see yellow spots on the top lead surface.

If you find these, you are dealing with downy mildew.

While it is treatable, it is difficult to get rid of completely, and smoking a leaf with mildew is dangerous, so you must destroy the plants immediately. Keep them away from the compost pile so they don’t contaminate any of your other crops.

Instead, you have to burn them. Just don’t stand face down while burning them – you don’t want to accidentally inhale spores, ash or not. You can also bag and dispose of the plants.

4. Powdery Mildew

12 Cannabis Diseases and Problems to Watch Out For

If you are growing your plants outside and you are dealing with a hot, humid summer, your plants could end up with powdery mildew. You will be able to identify it easily, as it will look like your plants are covered with white velvet.

If you catch it really early you may be able to treat it with a garlic or neem fungicide. If it affects more than 5 to 10% of the plant, you will need to tear them up and burn them or dispose of them.

5. Gray Mold (Botrytis)

This is commonly known as “bud rot”. This will show up if you are growing in moist conditions, or if the plants have been watered frequently from above. What happens is that moisture gets trapped inside the buds and doesn’t evaporate properly.

12 Cannabis Diseases and Problems to Watch Out For

The flower heads may look fine on the outside but when you open them they will be fuzzy and disgusting.

6. Stem Cancer

Check your plants regularly for dark spots near branches. Stem canker is one of those diseases that can attack almost any species but is quite common in cannabis plants.

Like other fungal issues, there is little you can do to treat it. You must destroy the plants before they can pass on the pathogen to others.

7. Mosaic Virus

Maybe you got this virus inside you limp Plants first. Like cucumber and zucchini mosaic, cannabis mosaic virus is quite virulent and virulent. It appears as speckled gray or white lines on the leaves of your plants, such as a glass window or mosaic, hence its name.

Be ruthless because you destroy these plants. This virus is incredibly contagious and will spread throughout your garden if you leave it. As always, fire is the best and only way to purify the virus. You will then need to treat the surrounding area with a fungicide, and do not plant anything edible or medicinal there for 5-7 years.

8. Green Algae

Do you see a slimy green algae crawling on top of your soil? Yes, this happens when you are watering your plants with great enthusiasm, especially during the summer. Algae won’t harm your plants, but you’ll want to allow the soil to dry thoroughly before giving your plants another drink.

You can avoid this problem by never watering your plants when the surface of the soil is still moist to the touch. Let it dry enough that you can only feel the moisture if you put a 1/2 inch finger in it.

9. Root Rot

It is more common in cannabis plants than in marijuana, but can still appear in cannabis plants. Unless you pull and examine their roots, the plants will seem sick for no apparent reason. When you do this, you will find that they are brownish-black in color and melting into mud.

It can be caused by many different pathogens, and cannot be treated. This can be avoided only by watering with a small amount of warm water at soil level. Since this problem only affects individual plants, you won’t have to go on a flowering spree when and if you spot it.


In addition to the diseases mentioned above, your cannabis plants may be suffering from a number of nutritional deficiencies. The symptoms may look similar to those of the diseases, but the treatments are quite different.

10. Boron

12 Cannabis Diseases and Problems to Watch Out For

Do you see distorted, yellow growth at the top of your plants? Are the new growth tips thickened and yellow or brown? Then they may lack boron.

It is not the most popular element in the periodic table, but it is quite important for healthy plants. This is because it is important for the successful absorption of phosphorus and potassium by plants. If boron is low, plants will not be able to absorb essential nutrients.

11. Calcium

12 Cannabis Diseases and Problems to Watch Out For
12 Cannabis Diseases and Problems to Watch Out For 10

Do your plants have brown or bronze spots on their leaves? Then it is possible that they suffer from calcium deficiency. Be aware, however, that these symptoms can also indicate many cannabis pests or diseases.

This can happen if the soil pH is too low, or the water they are being moistened with is soft or filtered. This is usually not an issue of too little calcium in the soil, but not being able to access the calcium of the plant.

To make sure your plants can access the calcium in the soil, make sure you’re watering the right amount and check the pH of the soil.

12. Nitrogen Deficiency

Withered, yellowing leaves are often a big sign of nitrogen deficiency. When cannabis plants have enough nitrogen, the leaves are a brilliant intense green. Conversely, its deficiency is manifested in depressed looking leaves that turn pale and yellow.

Treat this by offering your plants nitrogen-rich compost tea at the root level.

Don’t let these various cannabis diseases stop you from trying to grow your own plants. Eventually, you will face problems no matter what you try to grow. Instead, treat them as part of a troubleshooting guide. Many of these problems can be avoided, while others can be easily rectified if discovered early. With awareness and diligence, your plants should grow well under your care.

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