Easy homemade mold and pest spray

Hello fellow growers - greetings from the lowcountry of SC. I’ve been following the forum for a while now and seen many different OTS product noted for mold and pest prevention, but I’ve been using a simple and cheap homemade mixture.
Mix 1 teaspoon each of potassium bicarbonate, unscented Castile soap and neem oil into a 28-32 ounce spray bottle and fill slowly with hot water. Put cap on, shake and spray plants liberally.
This spray can be used up to day of harvest and is 100% pet safe.
The potassium bicarbonate prevents / kills mold and mold spores and the neem oil prevents all kinds of pests. The Castile soap is just used to emulsify the neem oil and water.
I like making my own because I can go heavy or light on either or both depending on the need.
I have used this same mix in a commercial sprayer to treat infected oaks, maples, pears, crepe myrtles and the wife’s vegetable garden.
I used a hot double strength mix on an aphid infested jajpanese maple and it’s coming back to life.
Happy growing!


The only thing I might say is some folks report that neem oil adds a harshness to the smoke when used on flowering buds. Yes its safe from a health standpoint, but you might find the taste unpleasant.


There is no way on Earth I’d use Neem oil during flower (which is where most mold shows up)

Distilled water and peroxide is the safest means for controlling WPM and mold along with lots of air flow.


Right on - I hear you. During flowering I might cut the need oil in half - or totally out. The potassium bicarbonate is the anti-mold agent and works great.

I also agree and ounce of prevention is worth a pound of cure, but last year I had a beautiful amnesia haze that got eaten up with botrytis (yes, my fault) - however sprayed the crap out of it after cutting bad colas off and was able to save 6 ounces.

As far as flavor - you guys may be right, but growing outdoors in region 4 is tough with all our heat, humidity, daily t-storms and heavy fog mornings in the fall this spray works for me.

I will note if you mix too much potassium bicarbonate or use too often you will some some slight nutrient burn on tips of leaves, so go easy.

Thanks for the insight!

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You’ll see that too with H2O2, depending on how concentrated the mix is. I like it because I can use it daily and really douche down the plant. Outdoors in heat and humidity is tough for sure.

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Just to carry over info from another thread, many growers feel like neem oil can impact flower taste - so if only worry / issue is mold, just leave neem oil out of mix. I was advised to leave in the unscented Castile soap as it helps the potassium bicarbonate “stick” longer and can also help with some insects like aphids.

In fact I know a super high end landscaper that works on the resort sea islands and he tells me all he uses for most pests, funguses and mold on trees and shrubs is a heavy mix of Dawn dish soap and water. Definitely not advisable for cannabis, but interesting.

I am getting ready to harvest autoflower 10th week and I noticed white powdery on a couple of leaves. I used Bergman’s mold blaster yesterday. I don’t know if it worked.

This is my first grow, im not sure what I’m doing. I will try your mixture.

Can you share some thoughts on what to do?

Thanks much!

Remove all affected leaves and buds and toss out.

Maybe move the affected plant in mixed in with others to limit exposure.

Keep plant out of moisture if possible.

It’s also a good idea to defoliate unnecessary shade / fan
leaves to promote good air flow.

Keep an eye on it and repeat spraying as needed. Don’t be afraid to saturate plant including undersides of leaves.

Remove any discolored / damaged / necrosis or otherwise unhealthy leaves and / or buds daily as you are in damage control mode since you know spores are in your garden.

Good luck. Powdery mildew and botrytis (bud rot) are your worst enemies auto your healthy flowers.

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May also want to consider an early harvest; but still be on guard when drying and curing for more symptoms. As long as there is moisture present there is a risk of more outbreaks.

If it were me I might use a heavy potassium bicarbonate and water spray instead of one with other stuff. The potassium bicarbonate shouldn’t impact taste and plants love extra potassium during flowering. A heavy dose may cause some nutrient burn on the leaf tips, but nothing major.

I feel for you. - I battle botrytis every flowering. I ended up losing 2-3 ounces of beautiful amnesia haze last year. Get all cuttings of infected plant removed from area ASAP, but assume everything close has spores on them and pre-treat with Bergman’s spray or another treatment. It wont go away and it will spread like wildfire if unattended.

Thanks much for the advice.

I starting to see small white mold it’s already been in jars that I try to open daily I’m sure it was still too wet to go in but seemed close went I went away for a week any ideas I since taken it all back out to air but afraid to put in sun and probably too late to treat with spray? So close!


Spraying with a mix of water and potassium bicarbonate might not be enough. Looks like it has taken hold pretty well in areas.

I would try and remove all affected areas and then either spraying down liberally after removing bad material.

If you still have colas to dry you can make a solution of 1% potassium bicarbonate and water in a bucket and plain water in another bucket.

Dunk cola in potassium bicarbonate water, then shake out.

Then dunk in plain rinse water and shake again before drying.

Bergman has a good article on it - just go to site map if searching terms doesn’t work.

Good luck - but either way for your healths sake I wouldn’t ingest anything with mold or fungus - bad idea.

Does Bergmans mold control leave a taste on your harvested buds?

I don’t know - I have never used Bergmans.

Bergmans does have neem oil listed as an ingredient, and it is not advisable to use neem oil on flowers.

That being said I make my own blend similar to Bergmans that I used on a flowering amnesia haze. I ended up harvesting early due to bud rot. I dried the colas after cutting out rot and the smoke wasn’t bad at all.

Typically if no pests are present during flowering and you are just worried about mold / rot then just a mix of water, potassium bicarbonate and Castile soap — leave the neem oil out of the mix.

Neem oil certainly can’t improve the smoke of your flowers and I’d only use in dire case of pests like aphids, caterpillars or spider mites only.

Too late I have sprayed my flowering plants twice with the mold control. I’m just wondering if IGLM recommends it, someone must have used it with positive results, but I haven’t heard any favorable comments on its use. I hope I didn’t screw up by using it.

Hey! The only thing about that mold is it’s not typical bud rot. Bud rot is black or grey and just destroys bud in a day. That type of mold shows up when I put wet buds in a curing jar. In my experience it’s localized and does not spread. Just remove the affected buds and keep the humidity low.

I suggest next time to use the humidity control packets that are put in humidors for cigars in you cure jar. They hold the humidity at 60%. They are pretty cheap and work for a long time.

No worries - the only concern using neem oil is that it could change the taste.

Neem oil is non-toxic and shouldn’t hurt your plant, but typically I only use during vegetative stages.

The main concern where I live is botrytis - bud rot.

I use the spray noted above every 2-3 days minus the neem oil and it works good, but can give nutrient burn to leaf tips.

As far as specific use on Bergmans spray, just shoot a question to the growing support folks at ILGM if nothing in the literature on the product gives that info.

But as for me, I only use neem oil in my homemade spray mix during the vegetative stage or if I have pests during flowering.

The potassium bicarbonate and soap mix should be enough to kill mold / fungus spores.

Good luck!

Thanks for help ! I tried to separate the worst after drying more completely I plan to make it into edibles .I have a decarb and infuser.im new to that process as well ,I’ll see how it looks after first heat and go from there I’ll try your dunk and rinse .thanks so much I thought I had lost it all at first .will order silica pouches as well.im in ga. and yes couldn’t find a place with low enough humidity outside to take a chance and used a dehydrator (not we’ll) I’ll count you guys as part of my blessings this first year ! Thanks again !

Thanks cousin_virgil, going to use your brew minus the neem oil, I have 2-3 weeks on one plant and probably 4 weeks for the other which will bring me well into October ,which is wet and colder.

Should I check and adjust ph?