Bacterial and fungal controls for marijuana plants

When you run into trouble with your grow you’ll want to act as fast as possible to prevent bigger problems.

This guide will learn you all about bacterial and fungal issues that may occur with your grow.

Ampelomyces Quis Qualis

These are naturally occurring hyperparasites of powdery mildew. They form colonies on the infection, reducing growth and may eventually kill powdery mildew on cannabis leaves.

Rain perpetuates the life cycle of this beneficial fungus. A formulated powder is available under the brand name AQ-10.

Bacillus pumilus

Bacillus pumilus is a spore-bearing bacterium found in soil. It is resistant to environmental stresses, including UV light.

Bacillus Pumilus on marijuana plant
Bacillus Pumilus

The growth of Bacillus Pumilus on plant roots prevents Fusarium spores from germinating. A commercial product is available by the name of Sonata.

Application boosts the cannabis plants’ immune system, inhibiting fungal germination and growth.

Bacillus subtilis

Bacillus Subtilis is a naturally occurring anti-fungal bacterium found in soils.

It has proven to fight blight, gray mold, and several strains of mildew, yet has no adverse effects on the environment or humans.

For this reason, it has been approved as a fungicide and bactericide for use in organic farming. Bacillus Subtilis compounds prevent pathogens from colonizing crops.

This biological fungicide can be procured online under several brand names.

Two strains are available; one for foliage applications (QST 713) and one to be used as a soil amendment at the time of planting (GB03 or MBI600). 

plant protector

Buy Marijuana Plant Protector

  • Protect your plants from diseases
  • Consists of three 20 ml bottles
  • Enough plant protection for up to 20 plants
  • Suitable for soil, hydroponic and all

Barley straw rafts and pellets

Barley straw rafts are used in hydroponic cannabis systems to inhibit the growth of algae. Barley straw does not kill existing algae but does prevent the growth of new algae cells.

While barley straw has not been approved by the EPA for use in public waters, it is available for purchase by homeowners for hydroponics and private ponds.


The use of copper as a fungicide has been practiced for centuries. The most popular use today is in the form of Bordeaux Mixture, which combines copper sulfate with lime.

The purpose of adding lime to copper sulfate is to reduce the damaging effect copper sulfate can have on marijuana plants. It is an added benefit that Bordeaux Mixture is also effective in controlling bacteria.

Copper deficiency in marijuana plant
Copper deficiency

As such, it is a good combatant for plant diseases caused by fungi and bacteria such as powdery mildew, downy mildew, leaf spots and fire blight.

Bordeaux Mixture is a good option for controlling these diseases on outdoor grown marijuana plants, as it withstands rains, enabling its effect to remain on the foliage.

However, it should only be applied before the flowering stage. Use a diluted solution on young plants to prevent burning of the tender leaves.

Also avoid applying in temperatures over eighty-five degrees to avoid the leaves yellowing and dropping off the plants. Follow label directions before using.

Gliocladium – beneficial fungus

Gliocladium is a species of parasitic fungus living in the soil. It produces volatile organic compounds which are toxic to other fungi and bacteria.

Gliocladium protects Mary Jane from gray mold by suppressing spore production. It is best applied as a soil drench and is available under several brand names.

Hydrogen peroxide

This common product found in drug stores and supermarkets, at 3% concentration, is a natural treatment for algae, gray mold, Pythium and powdery mildew.

Using hydrogen peroxide on your marijuana plants will not bring them harm. Peroxide helps aerate the soil by adding oxygen and is both anti-fungal and anti-bacterial.

Cannabis plants can be fed a mixture of hydrogen peroxide and water as a fertilizer and disease deterrent, resulting in healthy plants.

Hydrogen Peroxide for marijuana plants
Hydrogen Peroxide

It can be misted on the leaves and/or applied directly to the soil. An easy way to apply is to fill a clean fertilizer spray bottle that attaches to a garden hose and feed as you would, say Miracle-Gro.

The bottle will have gallon markings on it. Fill the bottle with peroxide. When you turn on the hose, it will automatically dilute.

If feeding sick plants, add one cup 3% hydrogen peroxide per gallon of water.

Pour into a spray bottle and spritz the leaves, making sure to cover completely. For general feeding, add one-half cup to a gallon of water.

Hydrogen peroxide can also be added to the water in hydroponic environments.

It can be used to sprout seeds by adding it to the water they soak in before planting; they will sprout quicker and grow stronger.

Follow the general application recipe for the peroxide to water ratio if used to soak seeds.

Download my free marijuana grow guide for more tips on growing and protecting your plants.


Just as milk is essential to a healthy human diet by building the immune system and providing good bacteria to ward off infection, it works in much the same way for plants, including marijuana.

Milk is a natural germicide and may boost plants’ immune systems in much the same way it does humans. It is a formidable treatment for powdery mildew.

Applying weekly sprays of one part milk to nine parts water significantly reduces the presence of powdery mildew and will prevent it from forming if the plants are not currently affected.

When rinsing empty milk bottles prior to putting in the recycle bin, pour the diluted milk around your plants rather than pour it down the drain. Your plants will love it!

Milk also acts as a disinfectant. Dip your gardening tools in milk, rather than bleach, when sterilizing between uses.

Neem Oil

Neem oil is extracted from the nut of the neem tree, native to India.

The insecticidal component of neem oil is azadirachtin which when applied, stops insects from feeding and developing.

Neem Oil for cannabis plants
Neem Oil

Neem oil is an effective defense against antsaphidsfungus gnatsleaf minersmealy bugs, scale, thripswhite flies and root weevils.

Other components in neem oil have fungicidal properties combating gray mold, root rotSeptoria and powdery mildew.

The beauty of using neem oil in the cannabis garden is its low toxicity factor for humans, animals and the beneficial bugs you want to keep around.

Neem oil is so safe for humans it is an ingredient in many household items such as toothpaste, shampoo and cosmetics.

It is considered an organic control, will not harm the environment and can be found at local lawn and garden centers.

Neem oil can be applied as a foliar spray, soil drench and is safe to use in hydroponic systems. In the latter, apply one teaspoon per quart of water.

The oil will be taken up by the root system and distributed throughout, protecting the plant from attack.

As a foliar spray, test an inconspicuous area of the marijuana plant before applying to the entire plant. Wait twenty-four hours to see if it is well tolerated.

Once confirmed, spray the leaves lightly. This should be done weekly until there is no longer evidence of pests or disease.

Do not apply in extreme temperatures or during the day. Apply at night to allow the leaves to absorb the oil.

Marijuana Plant Protector

Buy Cannabis Nutrients

  • Fertilizer
  • Plant protector
  • Grow kits
  • Guaranteed shipping

pH Up and pH down

Maintaining the proper pH level of your cannabis garden, whether soil-grown or hydroponically, is vital to deterring the growth of disease-bearing fungi.

Highly acidic environments lend themselves to the fungi species that can be detrimental to your growing efforts.

pH Up and pH Down is used in hydroponic situations to adjust the alkaline and acidity levels. Tap water typically is at the 8.0 level due to the high alkaline content.

The optimum pH level for hydroponically grown plants is 5.5 – 6.5. Acids are used to lower the pH level, while alkalis are used to raise the level. Be sure to use a product labeled for hydroponic use or you can damage the crop.

Potassium bicarbonate

Potassium bicarbonate is a water-soluble compound often used to neutralize acidic soil in crops. It is now under consideration as an organic fungicide.

Potassium bicarbonate is a synthetic compound resultant of a combination of potassium carbonate, carbon dioxide and water and is found naturally in virtually all life forms.

Potassium Bicarbonate on marijuana plants
Potassium bicarbonate

It is most seen in crystal form or as a soft, powdery substance.

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.


Pseudomonas is a genus of bacteria found in water and plant seeds. The application of this strain became widely used in the 1980s as a way to prevent the growth of crop pathogens.

It is applied to the soil or seeds, in agriculture. It is believed the introduction of pseudomonas to the soil or seeds, induces systemic resistance of the emerging plant to pathogens.

The application is available by several manufacturers to control many fungal and bacterial diseases. Pseudomonas refers to a variety of species, so check labels for the particular fix you need.

Quaternary amines

This is a broad term referring to a class of compounds which act as disinfectants.

Its use should be confined to cleaning gardening tools and work surfaces, but should not be applied to consumable plants.

Sterilizing equipment and surfaces with quaternary amines will help guard against the spread of fungal pathogens to your cannabis or other plants. Check the internet for suppliers.

Silica and silicate salts

When silica is added to the soil, it provides a strengthening agent for plant cells; it facilitates thicker cell walls, which results in stronger stems.

The availability of silica to a plant’s roots provides a protective barrier, dissuading fungal reach into the inner workings of the plant’s ability to uptake nutrients.

Silica and Silicate Salts for growing marijuana
Silica and Silicate Salts

The plant becomes more capable of surviving stress once clad with the armor silica provides.

In addition, enhancing the soil with silica-containing materials help to keep it aerated, allowing free flow of oxygen. This is good news for Mary Jane and her counterparts!

Hydroponic environments can also benefit from the addition of soluble silicon added to the water solution.

The roots become stronger and healthier, resulting in increased yields. The addition of silica in either growing situation has proven to reduce the occurrence of powdery mildew.

Several forms of silica are available for soil or water growing media:

  • Syna-Gro Po-Tekt, a potassium silicate solution, can be used in the soil, hydroponic systems and as a foliar spray.
  • Pyrophyllite clay, and aluminum silicate in powder form, can be applied as a dust or foliar spray.
  • Silica stone is used in hydroponic systems and can be re-used after a thorough cleaning.
  • Greensand can be added to the soil to enhance the benefits of silica.
  • Vermiculite and perlite is available at garden centers. Mix it into the soil. Many potting soils come with the amendments already added.
  • Diatomaceous earth contains the shells of marine microorganisms. This amendment also serves as a control for soft organisms such as slugs, as the tiny shells pierce their skin causing dehydration through the loss of body fluids.


Colloidal silver has long been used as a defense against algae in swimming pools and hydroponic systems.

It serves to guard against plant attacking pathogens such as bacteria, viruses and fungi.

Pathogens are literally suffocated to death by the tiny metal ions attaching to their respiratory systems. It is a completely safe control, as humans, plants and animals will not be harmed.

It can be used in the germination process, as a soil soak or foliar application. In fact, colloidal silver has been known to strengthen many food-bearing plants, including their immune systems.

Marijuana plants will not be harmed in the least, as there is no such thing as overdose with colloidal silver.

Sodium bicarbonate

Commonly know as good old baking soda, this inexpensive medium has many uses, including homemade treatments for ailing gardens.

By utilizing baking soda in the garden, the cannabis farmer can prevent and/or control many fungal diseases. Baking soda also has the benefit of adding to the good health of your crop.

Powdery mildew will stunt the growth of your plants and eventually lead to their demise if not caught and corrected.

To make a foliar spray, combine one teaspoon baking soda with four cups water and one half teaspoon liquid dish detergent or, preferably, castile soap.

Spray the affected plants once every two weeks until the infection has dissipated. You don’t want to overwater due to the higher sodium levels than are in potassium bicarbonate.

Streptomyces griseoviridis – beneficial bacteria

That’s a mouthful, huh? This particular bacterium is available commercially and is used to prevent root rot, stem rot, wilt and various fungal diseases such as Fusarium, gray mold and Pythium.

Mycostop, RootGuard and Microgrow are a few products available to the cannabis gardener.


Fungi cannot make their own food therefore they depend on your beloved Mary Jane (and other foliage) for food.

Consider them the vampires of the plant world. When they appear there should be one goal in mind: attack and retreat!

Do you want to learn more about harvesting and protecting your plants from diseases? Download our Harvest Guide.

Sulfur can lower the pH level of highly alkaline soils and is also used as a treatment for powdery mildew, gray mold and Septoria.

If using as a foliar spray, test it on a few branches and wait a couple of days before applying, as sulfur can cause leaf damage if not applied properly.

Sprinkle sulfur dust on the infected plants, but follow directions carefully. Sulfur can be applied as a dust or foliar spray.

Sulfur in both liquid and powder form is available at most garden centers.

Trichoderma – beneficial fungi

Trichoderma is present in all soils and has been developed as a biocontrol against fungal diseases due to its opportunistic lifestyle.

It is parasitic in nature, forming on the roots and feeding on other fungi. Trichoderma has also been known to deter foliar fungal diseases.

Recent studies have shown that due to the parasitic nature, Trichoderma actually promotes healthy root growth. Check the internet for approved available commercial products.

UVC light

UVC lights are non-chemical fungal controls for the hydroponic or indoor growing system.

They can be placed in the air ventilation system to help eliminate algae, mold and mildew spores from penetrating the indoor garden.

UVC Light for growing marijuana
UVC Light

It is important to mention that if you have added beneficial microbes to your hydroponic cannabis system, they will also be eradicated, so you may want to think twice when considering this form of control. UVC lights can be purchased at hydroponic supply houses and online.

Grow the highest-yielding marijuana with our High Yield Mix pack.


In the growing trend towards green living and green gardening, many household items have once again come to light with available uses other than the apparent.

As a fungicide, add one tablespoon white distilled vinegar and one-quart water to a spray bottle. Spray your plants to kill powdery mildew.

Make sure you use a diluted vinegar solution. Vinegar alone is a great weed killer but is non-selective. Vinegar in its full strength will kill all vegetation it hits.

That about covers the dangers you can’t see until they have reared their ugly faces. Let’s now move on to controls for pests and other vermin.

FAQs about bacterial and fungal control

Does neem oil kill fungus on marijuana?

Regular application of neem oil can suppress a number of pathogens that can affect cannabis. but yes it can kill fungus on marijuana plants

Can UVC lights help in pest control for growing marijuana indoors?

UVC lights are non-chemical fungal controls for the hydroponic or indoor growing system. They can be placed in the air ventilation system to help eliminate algae, mold, and mildew spores from penetrating the indoor garden.

Is it safe to spray vinegar on marijuana plants?

Yes, it is completely safe to spray vinegar on your marijuana plants. As a fungicide, add one tablespoon white distilled vinegar and one-quart water to a spray bottle. Spray your plants to kill powdery mildew. Make sure you use a diluted vinegar solution

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


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

24 comments on “Bacterial and fungal controls for marijuana plants”

  1. Great information, great website. Having a problem with brown mold on my buds. Humid and hot here in Southern Illinois. Looked at the pages on bacterial and fungal control. Not exactly sure if mold fits into these remedies. Can you illuminate a bit on this, please? Thanks

  2. I used one teaspoon of apple cider vinegar mixed with half gallon of water and sprayed my plants. Did i kill them?

  3. Will spraying the root protector solution made by you on soil kill pythium. My first seedling died and I think it was due to damping off but I made the mistake of planting the seed in the same medium, and I can only hope it wasnt the damping off disease that killed my seedling, but I looked at your solution and see that it prevents pythium or makes the seedling resistant. My question is will it help if i sprayed it on the soil on top of my seed before it pops up and will it still be effective? Id hate to think my efforts will be in vain if the soil is indeed contaminated with this pathogen.

  4. Oh i should add i am almost 7 weeks into flower. The baking soda solution turned a lot of the a the stigmas a nice reddish brown. The resin glands are all still clear. Am not sure if i should harvest these plants now or wait for the resin glands to mature a bit more.

    • Ed,

      What is the point of harvesting unfinished Cannabis? Let it finish.

      The reason you burnt your plants is because the PH of baking soda is very alkaline. adding 14 tablespoons probably made a solution that was above 10 PH

  5. I used Serenade on some of my MM plants maybe 4 days ago because of a powdery mildew problem. I spayed them to drench but the next day or two it looked like it did nothing.. I had never used A baking soda/water solution before. So i read what Jorge Cervantes has written in his Cannabis Encyclopedia. He says to “spray with a saturation mix of baking soda and water to kill surface contamination to keep the disease in check”. “A saturation of baking soda spray dries to a fine powder on the leaf;the baking soda changes the surface PH of the leaf to 7.0 and powdery mildew cannot grow”. I also use the full grand master grow level of Advanced Nutrients line. So i have beneficial bacteria in my systems I also added another product from Botanicare called Hydroguard to my reservoir. Well i wish now i had come here first before spraying my saturation mix of baking soda/water on one of my 6 plant grows. The plants where very wet but where all healthy when i got done yesterday.They did not look so great this morning. Lots of dead foliage. I just got done picking off a lot of dead vegetation. I guess my saturation mix was way to strong to spray on my plants. Also i wish Jorge Cervantes had specified how much baking soda to add to the gallon of water. I had 14 tablespoons in solution and the water still was not saturated. I guess i put way to much baking soda in it

  6. So does that make silver toxic to humans if smoked? Via the same microparticles found in the plant (if treated with colloidal silver). I would think that would be an important to know to the grower.

  7. life time grower . inside pulled last crop . leavs cuping r curling up not takn water. now sprouts stemks purple n lower leashons, verry flustrated . hav spinal problms trird lumbar graft. cant smk dammit / injest and up anal stops leakage best street pot sucks.mor seeds coming thanks,

    • Lesions as in skin cankers?.sounds like a special kinda fusarium that fucked my babies up.Aka Stem Blight which was so hard to get rid of the branches get brittle it was a night mare .if u use alcohol or peroxide you’ll be able to wipe the cankers and purple off and if it does then it is Fusarium Stem Blight for sure

  8. Don’t spray colloidal silver on your plants!!!!
    It’s used to turn plants in to hermies for the creation of feminised seeds, so unless you want male flowers DO NOT use Colloidal Silver.

  9. […] The problem with this infection is that, since it travels underground and starts at your plant’s root system before hitting the rest of the plant, it is extremely difficult to detect until it’s too late. You will probably start paying attention when your plant’s leaves start wilting and turning yellow with brown edges. If you examine the roots, you will be able to notice the Pythium. Otherwise, however, the symptoms will just be like any other fungal damage. […]

    • I’m a newborn 1st time grower has anyone used diatomaceous earth? I’ve had gnats and sprayed with buddi all rounder, now I wondering if the diatomaceous earth will kill any eggs in top soil. Tx for any help it will be most appreciated.

  10. Colloidal Silver does NOT directly work against viruses. All curative agents have what is known as a mode of action, or MOA. We must understand the MOA, in order to comprehend whether a treatment will have any impact. Colloidal silver has an MOA that has been known for decades, yet recently Google has been geared to bury it with only articles stating “the MOA is being explored and we think it is ….(followed by disinformation)” and the obvious purpose of deception is most likely tied into the current Ebola fear campaigns.
    This is how colloidal silver really works (its MOA), following an example: Colloidal silver is to bacteria what cyanide is for all red blooded organisms. In red blooded organisms, cyanide binds with hemoglobin thereby effectively replacing oxygen, which makes it impossible for blood to carry oxygen. Given enough cyanide, oxygen starvation via cyanide bonded hemoglobin, and the result is death (often in minutes)
    Colloidal silver does the same for bacteria, it binds with the oxygen carriers in bacteria permanently, causing bacteria to quickly die from oxygen starvation. This is the MOA for colloidal silver, which has been clearly known practically forever.
    Viruses do not have a metabolic process that requires an oxygen carrier, therefore colloidal silver is will however clean up secondary bacterial infections that usually move in after a viral attack. My knowledge stems from studies on human health, but this particular bit of info should cross pollinate with plants since the basic fundamental components of bacterias and viruses that affect both species are relatively similar..cheers, and happy growing..

    • So, it might not be a good idea to use it if ising any bacillus product to kill fungi, as it would kill (or inhibit) all bacteria, including beneficial ones.

  11. dont you think”neem oil” deserves to be on your list as a great general fungicide that can be applied as a foliar spray or root drench for prevention and cure,peace jas