Leaf Spot Fungus (LSF) aka Rust Spot Control?

Need recommendations how to eradicate leaf spot fungus

neem-oil and potassium bicarbonate. Are you in the flowering stage or vegetative?


Well it would be okay up until the first 2 weeks of flowering and not sure about after that. Other suggestions would be to do it right before lights out. I would turn off your grow lights and keep the other lights on and then make sure that they are totally dry prior to lights out. I also recommend that you increase your air flow via fans. 1. Airflow, airflow, airflow = get a fan on plants early and keep the air moving all the time. You can never have enough of air flow
2. Humidity = keep it 40 - 60% max. If you don’t have a humidity measuring device, get one.
3. Soil, hydro, or coco = use some kind of silicon protective supplement like ‘Pro-Tekt’ throughout plant life.
4. *Foliar spray = early, throughout veg (one a week or so), and first two weeks of flower.


Bergman says, "Potassium bicarbonate is an effective defense against powdery mildew, Septoria leaf spot, blight and many other fungal diseases. To apply, mix three tablespoons potassium bicarbonate, three tablespoons oil and one half teaspoon castile soap with one gallon water. Pour mixture into a spray bottle and mist the cannabis leaves. (This also works on most edible plants).

Potassium bicarbonate can be purchased from garden centers, hardware stores and pharmacies, or can be obtained online under various brand names."

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I’m reading Bergman now, we have several other the threads about this going I have like 8-9 fans include three 9 inch high velocity fans,one that I leave in the tent when it’s humid along with the two others that are always in there

I know exactly where this started I have a picture of it. anyway I’m going to my hydro store now this guy has an agriculture degree I’m going to see what he says

On Bergmans site I saw a @latewood had a lot of input with this and I’m going to invite him to this thread

thanks, I’m going to come back and re-read what you said in a little while, I’ve got to bounce right now but thank you very much @durabloom

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Do your leaves look like this

rust, how many of you have had this and been beaten by it? lots i bet!!!
first, rust is a fungi. it is opportunist. it preys on unwell plants. if something is a miss, rust is a sign. rust has been identified to have 7,000 species. it attacks crops of every description. but we’re only interested in one variety arn’t we?
if rust is present early in a grow, you have problems as it’s an indicator something in your room is a miss. usually ventilation. go through your system and double check things are in place and working properly.
rust is an air borne fungi. if given the opportunity, it WILL take hold. it usually does during flower as this is when the plants immune system is at its weakest as its energies are concentrating on re-production, not survival.
depending on what part of the grow you get it, you can cure/minimize it with either chemical or natural remedies.
it enters the leaf via the stomata and then it’s off and running.
fungacides used are generally copper based and include; thriram, manzecob, maneb or zineb at 10 day intervills.
baking soda, 1 tea spoon/ quart of water. spray on.
copper sulphate, read lables.
fungacidal soap sprays;
garlic sprays, 1/2 cup minced garlic, 1 quart of water. let sit 24hrs, strain, spray.
sulphur, one of the best natural sprays. it is low in toxicity.
micro kill, a citric based killer. i use this with great successfff

Hope this helps



It does help thanks will

I’ve just come back from my hydro store I’m going to fight it with baking soda and neem oil and perhaps the garlic spray they had one already made but I might try my own

I also purchased mychorrazide because it says that strong roots and a lot of nutes help to slow it as well

The best news is if all else fails they have a gas-like Fogger product and also there’s a spray of the same product, I think it’s called chlorine dioxide but I’m not sure and I’m hesitant to Google it because I already have men In black following my every step, I don’t need any others.

She said that she’s used it with 100% positive results. I left the pamphlet out in my car so I’ll add the products name/url in later edit @hammer

sulfer burner works best it leaves a film on all plants best run at lights out


How exactly does is work @donaldj, do you know? I’m curious.

it vaporizes sulfur prills the vapour is toxic to most pests but as it settles it leaves a film of sulfur on plants which is toxic to fugi and molds as well as most bugs
It does require you clean up before flower washing leaves etc. but highly effective against molds https://www.youtube.com/watch?v=UcJhUEF9Tas


I have read some thing from an LED supplier not to use sulfer burners if you use LEDs it isnt good for them.
I cant remember why but I will tell you when I remember.
You can just removed the LED while treating.

Hey @Donaldj I put neem oil on this morning looks good so far, I don’t see flower till 9 Eastern but I’m hoping for the best

my question is when do I spray on the baking soda ?

Do I wait, or do I want to spray it right now, because I’m thinking it might wash the neem oil off ?

… is 1 teaspoon per quart the right amount and do I mix with it anything else ?

Here’s a tip for everyone

If you’re ever going to spray anything on your leaves just spray it on one leaf and wait at least 24 hours

I just learned this on YouTube. I went looking for this information after I sprayed baking soda at the recommended dosage on all my plants, unfortunately frying 3 OG Kush plants.

I wish I had known this prior, now you do.
-good luck

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Did the baking soda thing work?

I guess it’s kinda relative ? …it seems to slow things down, but some plants seem more susceptible than others

I’ve learned while making seeds that nothing bad likes the taste of a plant that I’ve sprayed with colloidal silver. So if your problem is bad enough you can spray your nodes at the base of stems 3 times a day for the first two weeks of flower using a good 220ppm colloidal silver and you will get yourself a healthy female that turned herself into a male with no y chromosome. Fem seeds and fem pollen. Flowers still as well. You can spray your walls or mold or anything you don’t like. Bad things hate colloidal silver. Do some google on it…


@durabloom @Hogmaster

Can anyone recommend a good product that uses potassium bicarbonate? Had trouble finding it at the store.

Also, is this meant to prevent further spread of leaf rust, or kill/cure it on the spot?

Lastly…in the meantime I have a sulfur spray I’m going to use…do I need to rinse the leaves off with clean water 24 hours after the application, or can I spray and leave as is? Tnx!!