Diseases on marijuana plants

Diseases on marijuana plants and infections (cannabis diseases) usually create the worst possible issues for your plants. They have a tendency to be much harder to treat than pests. Diseases in your plants will usually come in one of two major categories: fungal or bacterial.

Fungal diseases are often caused by environments that are too damp or humid, or places which lack airflow. Fungal spores float around in the air looking for a suitably damp place to root down and if the environment is right, that suitably damp place might be on your cannabis plant.

Bacterial infections are often sneakier and harder to notice. They are spread by a number of different possible vehicles, ranging from insects and humans to rain and unclean soil or substrate.

Bacteria can sometimes get into a plant and then leave it mostly untouched unless the plant is weakened by external stresses, at which point they can quickly take down the whole plant.

Download my free marijuana Grow bible to know more about diseases on marijuana plants.

Proper treatment of a fungal or bacterial disease requires a knowledge of the potential symptoms, which we’ll list below. As always, the best defense against disease is prevention. Do your best to create an environment which is healthy for plants and inhospitable for fungus and bacterial growth.



Hydroponics systems are water-based, and without proper care, they can become havens for algae. Both cannabis and algae thrive in nutrient-rich water environments, but you really don’t want them to be sharing the same space.

Algae will live on the roots of your plants, and thus deprive your cannabis of the nutrients necessary for the plant to develop properly in a hydroponics system.

Not to beat a dead horse, but your best defense is always preventative. Do your best to minimize the potential for algae growth before it occurs by the taking the proper precautions beforehand. Because algae and cannabis have similar requirements of water and light, it can be difficult to do this.

The easiest way is to make sure that no light reaches the roots of your plants. Use an opaque, dark material to block out the light. If algae begins to develop, clean it out right away.

Read more about Algae on marijuana plants

Bud Rot

Bud rot

Bud rot (also gray mold or botrytis) is one of the most damaging of the possible infections your marijuana plants can face. It eats every part of the plant, not bothering to distinguish between buds and flowers or stalks and stems.

The infection can spread very rapidly, so you want to take precautions to avoid letting gray mold take root in your plant’s environment. The disease prefers a cool but relatively humid environment.

Keeping the temperature in your grow room above 70 degrees Fahrenheit will help, and make sure to monitor the humidity constantly so that it doesn’t get too wet.

To grow healthy marijuana plants despite moisture stress, make sure to get seeds with strong genetics. Usually, they fare well even in harsh environments. I have created multiple grow sets which features all you need in order to grow healthy plants from seed to harvest!

buy all-in-one marijuana grow set

All-in-one grow kit

Another step can be to change clothes or wear protective gear before going into your grow room. The spores can attach themselves to clothing fibers and then release in the grow room if the environment feels appropriate.

If all else fails and your plants develop gray mold, there a few different soaps and sprays you can use to help mitigate the damage and treat the plant. Marijuana Plant Protector is the best solution.

Read more about Bud rot on marijuana plants

Leaf septoria

Leaf septoria on marijuana plants

Leaf Septoria (also known as yellow leaf spot) produces yellow spots on the leaves of your cannabis plants. It’s a fungus which usually pops up on outdoor cannabis plants after they have been exposed to both heat and recent rain.

The yellow spots initially develop on the lowest leaves of the plant and then work their way upwards. In the worst cases of Leaf Septoria, the entire leaf will turn yellow and begin to crumble. Generally, however, the leaves won’t die off, and the plants will survive.

Despite the fact that it isn’t usually lethal, yellow leaf spot can heavily inhibit the growth of the plant and its eventual yield. You can prevent yellow leaf spot by keeping the soil well-aerated and applying a fungicidal compound to your compost.

If you still have trouble with yellow leaf spot, you can apply baking soda as a reactive measure.

Read more about Leaf septoria on marijuana plants

Powdery Mildew

Powdery mildew

Powdery mildew on marijuana is a spore based fungal problem that can affect both outdoor and indoor marijuana gardens. The spores are transmissible through the air, and being carried by wind means it can be fairly difficult to protect against.

It’s also a very sneaky fungus because the spores can lie dormant in the soil until conditions are just right for them to start growth. Usually, this is when the environment is warm and highly humid. 

Also read Symptom checker – Identify marijuana plant problems

Powdery mildew also occurs frequently when the cannabis plants are too close together, and there isn’t enough airflow. An overcrowded grow room unnecessarily risks damage to your plants.

You can recognize powdery mildew by its white color. It will cover the foliage of the plant and inhibit the photosynthesis process.

To make sure you don’t see any issues with nutrients arise in your next grow, I have created a balanced nutrient package, specifically engineered for growing marijuana plants!

buy marijuana fertilizer set

Fertilizer package

  • Give your plants the best chance to live
  • All the nutrients from seedling to harvest
  • Enough nutrients for at least 5 plants
  • Say goodbye to nutrient issues!

If your plants suffer from powdery mildew, there are a number of safe naturally-based sprays you can use (including milk and apple cider vinegar) to help deal with the problem. Mold control also treat powdery mildew. 

Read more about Powdery mildew on marijuana plants



Fusarium on marijuana is another fungal issue. Instead of eating the foliage, however, fusarium damages the root systems of your cannabis plants.

Thankfully, hydroponics systems aren’t affected by fusarium since it requires a soil-based substrate to survive in. Usually fusarium causes wilting in the plant or a more generalized root rot. Like some of the other fungi, fusarium will sometimes lie dormant in the soil for long periods of time, just waiting to strike.

Know how to perfectly time your harvest so you can maximize your yield. Download our free mini harvesting guide.

If fusarium does begin to take hold in the root systems of your plant, there’s very little that you can do to treat it. First of all, it’s very difficult to spot until it’s too late.

Second, although indoor growers can help prevent fusarium by using sterile soil, there’s no way to be sure it isn’t present outside in nature. Read more about Fusarium on marijuana plants

Verticillium wilt

Verticillium wilt

Verticillium wilt on marijuana is fairly similar to  fusarium wilt, except that it is mostly like to appear in soils that are improperly drained or overly full of nutrients.

The first signs of verticillium wilt are drooping and yellowing foliage. The fungus will also cause the stem to turn a dark brown at the base, where it makes contact with the soil. These sorts of fungal diseases are nigh impossible to treat, so it’s of the utmost importance that you practice preventative care.

Try to make sure that your soil or substrate has proper drainage, so that verticillium wilt won’t rear its ugly head. Because there’s really no way to cure or treat verticillium wilt, make sure that you rotate your crop if you have issues with it, otherwise it will just keep coming back.

Read more about Verticillium wilt on marijuana plants.

If you want to protect your plants against any diseases, please take a look at my Plant Protector set, which is made especially to protect marijuana plants!

Marijuana Plant Protector Set

Buy plant protector set

  • Protection against diseases and pests
  • Consists of three 20 ml bottles
  • Enough plant protection for 20 plants
Bud Rot

Root rot

Root rot, also known as Pythium, is a fungus that will live on the roots of your marijuana plants. As you can imagine, this isn’t good for the roots, and if it’s not good for the roots, it’s definitely not good for the plant.

Root rot can occur both indoors and outdoors, and in a wide variety of substrates, including the water of hydroponics systems. Initial symptoms include wilting of the plant, and a change in the color of the foliage to brown or yellow.

Since these symptoms can be caused by a wide variety of issues, you’ll need to check the roots themselves if you want to verify the source.

When a plant is infected by pythium, the roots will begin to change color and eventually the outer layer of the roots will be shed to reveal stringy, weak inner core.

You can help keep your plants root rot free by fastidiously cleaning the hydroponics system and making sure that the substrate drains properly. Remember, preventative care is key!

Read more about Root rot on marijuana plants

Damping Off

Damping off

Damping off of marijuana seedlings isn’t actually a disease, instead it’s the plant responding to the presence of a disease.

You’ll notice when you see damping that the plant seems like it’s wilting— it may resemble overwatering, but really it’s the roots which causing the issue. Damping off usually occurs in cannabis seedlings. The plant itself will develop lesions before actually dying entirely.

Again, preventative care is the only real way to deal with damping off and other fungal disease-related problems. Usually, plants won’t be able to bounce back from damping off, and so it’s up to the grower to prevent it from happening in the first place. Read more about Damping off on marijuana seedlings

Marijuana diseases FAQ

Can Algae Grow on Marijuana Plants?

Hydroponics systems are water-based, and without proper care, they can become havens for algae.

What Causes Bud Rot?

Bud rot (also gray mold or botrytis) is one of the most damaging of the possible infections your marijuana plants can face.

What Causes Fungal Diseases on Cannabis Plants?

Fungal diseases are often caused by environments that are too damp or humid, or places which lack airflow. 

Thanks for reading. Please leave comments or questions below and don’t forget to download my free grow bible

Happy growing!


Avatar for Robert Bergman

Robert Bergman


Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations ... See profile

40 comments on “Diseases on marijuana plants”

  1. hi, I wanted to ask for some advice on my outdoor plants, I have several 5 foot plants that started flowering about 3 weeks ago and well now most of the buds are turning brown and seem to be drying up, I did give them a dose of ‘Maxigrow”. Since I had transplanted them strain into the ground I have been giving them about 10 gallons of water every other day or so when I gave them the “maxi grow” I am wondering if I gave them too much or if it was too early ? they act like they are done flowering already but they have barely begun to get buds, is small early brown buds a sign of nutrient overload,. or is it something else like possibly root rot or bud rot or something else?, I looked and the roots still seem white and leaves are still nice and green? I have trieed to just flush them now strait water for the last 2 weeks but only very top buds are still white. My friend is using the same strains and his plants are still growing now 6-7 feet tall and barely just getting white pistols>> I think I messed up this year is there anything I can do or give them to help now ? thanks

  2. Yo RB, I’m having an issue I’ve never seen before.. In week 3/4 of flower I notice on part of one plant the leaves are wilting as if it’s stressing from under watering. On examining these stems I see that they look severely pinched, about 10cm up from the base, and in some cases split apart, though not soft or wilting like damping off. I isolated the plant, and after ensuring it was not over watered, just gave it water and after 48 hrs part of it seemed ok, though not the stems with the issue. I took those stems off and the remaining plant seems fine, though reduced by about 70 percent! All was fine, then about 2 weeks later, almost over night, another plant had the same symptoms and I lost another 70 percent. Both plants were near the heater, but there are other plants the same distance that are fine. Can’t find solution in any of my books or online. Any ideas?

    • Hey friend, seems like we have a common problem. I have 2 w.w. That are 2 to 3 ft. Tall and then I have 2 more that are 12 to 16 inches. All things are the same. Water, nutes, soil, light, I’m new to autos! But the consistency is something to be desired. If you figure it out? Please let me know. Have a good one hoss.

  3. Can I mail /post you a picture of my backyard container marijuana plant?

    Its leaves are reddish and I don’t see anything in your photos that have this particular hue. I don’t know how to repair it until I hear back…thanks for your time!

  4. Good article, thanks for sharing! I have found that 1tbs baking soda and 1tbs organic dish soap worked like a charm!

  5. Rita,

    It is hard to determine the issues you have with your auto flower WW.

    Auto flower genetics have hybrid tendencies. Best bet for you; Join us at support.ilovegrowingmarijuana.com for more info and friendly support

  6. Hi, I’ve harvested 3 white widow auto so far this year, but all three did weird budding. How long is the budding period once she starts to flower? Next batch of seeds only had 50% germination success, even after soaking, and two of those aren’t growing well. These don’t seem to be consistent where the growing conditions have been the same…

    • I start 4 at a time. Misdemeanor in Ky, I’m having the same problem. 2 are about 2 to 3 ft. Tall. 2 are about 1 ft. All are under same light same soil same amount of light and same amount of nutes and water. Some days a diamond, some days a stone! Good luck wish I could help you! But evidently I need to learn more about inside growing.

  7. After growing in the same manner for several years, a few weeks ago, I noticed a white film seemingly growing on the stems of my plants. This film was about two inches above the rockwool, and did not extend much above this central stem area. When I rubbed the substance, the stalk basically degenerated between my fingers, turning into stalky strings. The stem at this point was brown and dried,I quit rubbing the white film, because the stem was literally dissolving. . Three plants still have some stem. What is this stuff??? I can’t find any thing in any books. Stem subjects always seem to bring up root issues.The roots are fine-when I pull the plant by the base to throw it away, the roots are white and plentiful.

    • rick,

      We need you to join our forum and share a couple pictures. I would have said it is some kind of rot but, you say the roots are fine. There are a couple worms that can move into the stem and eat it from the inside.

      I suggest you go here: support.ilovegrowingmarijuana.com and we can help you out and provide more informed advice. Good Luck

  8. Over 80+ % of North American cannabis plants are systemically infected with either a viral, bacterial, or fungal pathogen. Proven facts!
    Environment and care dictates the devastating expression of these pathogens. Knowing this, there are very few alternatives to a remedy.
    BTW, Fusarium Solani claimed numerous hydro crops of mine personally. Did not know what it was until I cultured it and took it to a lab for results.
    Yes, Fusarium Solani in Hydro, Re-circulating Deep Water Culture all Inert Mediums even!
    I’ve solved all my genomic parasitic issues, even those introduced by vectors.

    Good luck all!

    • Hi John,

      Unfortunately that’s not possible, we only offer the root protector as a set together with the mold control and bug blaster.



  9. I have a problem with my plants . The upper growing shoots are turning a brownish color and it is spreading to healthy plants at a rapid pace . When flowered the lower flowers become completely brown and dried out basically dead . I have never experienced anything like it in 25 + years growing indoors .. What could it possibly be ? It didn’t appear until I noticed a fungal gnat infestation and now that I have it controlled it seems to have gotten worse 🙁 any thoughts ? Need help badly , thank youb

  10. I’m receiving 4 starters from a friend this month, and will utilize your book for guidance. Three will be in a friends garden (Mohawk Valley, OR) while the 4th will be near my home among the blackberries with lots of sun. I’m excited for my first ever grow. Thanks, I’ll keep you posted. -Brian

  11. […] The substrate is important because it sort of acts as a trap for nutrients and important elements. For example, if you are using soil, you need to make sure that it is well aerated. Good circulation among the roots is very important since that is where your plant will be picking up a lot of things to absorb. Roots need oxygen, regardless of the substrate you use, whether you are using traditional soil or newfangled hydroponics equipment. Plus, proper aerification will minimize the risks of disease, mold and fungus on your marijuana plant. […]

  12. The service you have provided me with this far has been outstanding! The ordering process, the delivery, the quality of the products is also outstanding. My femenized seeds are 15 inches tall at 4 weeks from sprout and all 5 plants are healthy and thriving. Thank you for you expertise. I’m looking forward to my end product: meds that relieve knee pain, anxiety and adult ADD. Thank you!

    • Hey Lisa Thanks for sharing. We are glad you enjoyed doing business with us. If you have any question don’t hesitate to contact us.

  13. […] By Robert Bergman, ILoveGrowingMarijuana.com […]

    • the tops of leaves show silvery patches with microscopic shiny black spheres. I also have leaves get speckled all over with brown,, spots, yellow color and turn brittle.. I remove affected leaves but the symptoms will basically overwhelm the plant.

    • Hello I amHello I am wondering how often do I feed and water my seedlings? The feedingThe feeding schedule tells me how much fertilizer to put in the water but it does not tell me How often tohow often to water or how often to fertilize. Unless I justUnless I just missed this information while I was reading. Any advice woAny advice would be great thank you very much!

  14. You water plants in pots when they are almost completely dry. This is a method that takes a bit of practice, but not for long. it won’t be long until you can physically measure when the pot gets too dry.

    Follow nutrient label directions. Or; Go to Bio-Bizz to get recommendations (nutrient calculator) for how to ix your nutrients.

    • I’m using grow bags and it’s really easy to check for water by weight of the plant in the grow bag. That and an index finger 2 knuckles deep works for me!

  15. Hi just wondering if you can help I have just grew 1 plant didn’t get much of it what my problem is I don’t know how often to water I also use bio bizz grow my next three are in veg since I done my closet in reflective floor and walls they seem to be loving it I also give them yeast co2 since the room was finished the new leaves are growing much bigger and wider they seem to love it in there so please please can you help me with a water and feeding program’s scared I wreck these ones to ps one is sativa and the other two are indica there just stunning please help a novice learner thank you in advance x