Alternaria/early blight

I have two plants that appear to have contracted early blight. One is much worse off than the other. I’m looking for some advice on how to move forward.

They are both around 3-4 weeks flower. The one smaller plant has had one lower side completely ravaged I plan on removing all severely affected limbs and any leaves form that side of the plant to try and protect the rest. Then plan on following up with some kind of fungicide treatment possibly potassium bicarbonate, I’d like to try bacillus subtilis as I’d like to stay as organic as possible but I’m having trouble sourcing some where I am.

As for the second and larger plant the damage/infection isn’t nearly as severe it is like to get on top of it as quickly as possible. I’m going to clean up the inside of the bush, spread some branches to promote airflow, remove affected leaves and treat with the same treatment as the other.

A few questions and comments I have for the forum are:

  1. Is this alternaria? I’ve never seen anything like it on cannabis and until now wasn’t even aware it could be affected.

  2. What are my foliage treatment options? I’m in flower so I’d like to stay away from sulphur or copper based fungicides, I’ve heard potassium bicarbonate works on blight for tomatoes but have also read about its potential to burn pistils. I’ve also heard of milk water mixtures working for wpm but not sure it would for this fungal infection.

  3. What are the chances this spreads to the buds and how potentially harmful is it if it does? I always bud wash my outdoor do deal with dust bugs and any mildew spores but everything I’ve read about alternaria basically says to scrap and burn the plant. Would the bud wash kill any harmful spores prior to smoking?

Thanks in advance for any advice I’m pretty gutted about this whole situation, my big plant was probably the best I’ve grown so far until now.

Those rusty looking spots shout Cal mag deficiency to me but I’m a beginner the pros will be here soon @Underthestairs @PurpNGold74 @ThermoNukePanda @MidwestGuy what your guys opinions


Tis mold of some type. Some people use a dilute milk spray as at covers and protects leaves, but I don’t know that it addresses existing mold. I have heard of people using baking soda as well. Sodium bicarbonate is toxic to fungus. I would personally use a dilute spray of hydrogen peroxide.


I’m a little over my head here. You’ve got some good tags. I’m throw in @Covertgrower and @Myfriendis410


Definitely not calmag problem :confused:


Hydrogen peroxide is definitely safe. Stay diligent, but likely you’ll only be managing this situation. It’s outside and a lot of variables here.

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Outside my wheelhouse as well. Solid advise above.

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I’d remove all affected leaves and branches then spray the rest of the plant with h2o2 and water mixed 50x50 every evening for the rest of its life. I’m dealing with bud rot on one of my plants due to poor air circulation. Every couple of days I find new mold damage.

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I’m gonna go ahead and strip and spray is that 50/50 solution using 3% h2o2 or higher?

3% is what I use I soak the crap out of them to make sure I get everything

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