Let's talk about powdery mildew

Let’s have a conversation about powdery mildew! What advice do you have for growers dealing with this stuff? Have any suggestions for treatment and prevention?



I am making the assumption you are growing in a greenhouse. If you are not we need to talk other strategies.

Control the humidity. So that it is not a problem. Propet airflow really helps.

The second issue with fungal diseases in glasshouse production is looking at growth medium and nutrition. Most of the big problems that are not solved with environmental control, are generally linked back to a nutritional question.

The VPD advocates and I agree with there research also plays a big role. The issue I have is with no practical experience with VPD control profilings in glasshouse production.

Post infection you have a number of choices

Organic, I have found backing soda and a non detergent dish soap. Useful. Not perfect. If your state allow organic oils. Like the old sun oil. You can do baking soda, sun oil and a non detergent dish soap. The dish soap works makes the water wetter. The sun oil makes this work much better. This may be the only time you want the humidity high when you spray. The longer the solution stays in contact with the powdery mildew the better. The exact recipe is dependent on the pH of your water and it’s buffering capacity.

If you are in a state that allows organic uses of copper Cu8 this great product for many greenhouse crops for powdery mildew control. It is a bit funny to work with. If you want more information just ask.

Inorganic products are also available. You will have to see what is legal in your state.

For most foliage fungus you have to pay real attention to humidity especially at transition times of day. Automatic control systems really help.

This means at when you can lower humidity by bring in outside air and heat it, I spend the money on heat. On this line I like Acme Jet fan

I also like other types of fans for growrooms.


When I’m visiting a grow facility with powdery mildew issues my perspective is focused on getting the problem under control and then prevention. Extreme Microbial Technology (EMT) brings to the market the latest & greatest in PCO technology. Our Microbial air scrubbers act as a fire hose when bringing a mold bloom to its downfall (with out being toxic to your employees). We have real world success stories along with university studies that validate what we can do to improve a grow facility. The other tools we utilize help us quantify the scope of the mold problem and reduce the guess work when determining a course of action. EMT can play a pivitol roll in solving a facilities problem and sizing up the system to combat the problem. We can demonstrate that that what we do works, in real time, with our BAMS (Bio Aerosol Monitoring System) unit. We really do have a cutting edge quiver of solutions for the cannabis industry as it relates to mold and pathogens.



Who did you work with at Kansas State?


Hi, brand new here and this caught my attention as I was just helping someone with PM and bug outbreaks.
PM can be a nightmare and never allow the plant to reach it potential. You can spray evey oil, soap, chemical pesticide and the PM wil come back during flower then your up a creek.
I would start will sulphur. As in elemental sulphur. Do your homework on it and be open to using it in foliar spray, water in, top, dress.
Next add and mix Silica with it but not from Potassiumm Silicate. Silica from Silicon Dioxide. Endo Mycorrizia work with Silica for super strong wood and silica will build a barrier over the leafs own natural cuticle as a extra barrier.
3rd use microbes a fungi called Streptomyces lydicus. It protects against root decay and will colonize on planta leaves and tissue and act like Dyson.
Fight PM systemic, on contact, and with microbes.
And eveything I mentioned is organic. I have sprayed on hot summer days at noon, or at night and beat Downy Mildew under the leaves with PM on top of the leaves on my softwood Summer Squash and it’s safe for cannabis.


You can make huge strides by swapping out genetics. Some strains and cuts I’ve had are particularly susceptible. Obviously, humidity - VPD - temperature - airflow - plant health - cleanliness all need to be dialed in. There are regional considerations that play a factor as well, in Colorado I rarely had pm but here on the east coast it’s been persistent.

Zerotol cures at 37ml/gal.

Milstop 5.6g/gal + Neemoil 5ml/gal + NuFilm 1-2ml/gal (tank mix)
Heavy 16 Foliar 75ml/gal
Cease 38ml/gal

There was a thread that I can’t seem to find now, but someone was talking about raising the temp (x) degrees for (x) amount of time each day. Has anyone tried that?

The extraction guys I’ve spoke to told me not to burn sulphur because it messes up their product and I don’t remember the explanation, can anyone chime in on that?



I like sulfur, we just used to sublimed it. Had less luck with using sulfur in any spray form.

We where early using yeast as a colonizer. We has mixed reults at first and then got pretty good at it. We took the idea from hot house strawberry growers. We had 5 good years of test data. Every time we added foliar nematodes for thrips prevention we added the yeast to the spray. We found that low pressure application of both the yeast and nematodes worked great. The trick with local yeasts is in the first rounds of collection, and getting reliable at identifying it. Later we started saving the local yeast by season and freeze drying samples. I wonder if Kansas state plant pathology has published any of the work we did with them?

I would might worry using Streptomyces spp. as a controller the ascomycite stage looks to close to other members of the family. I would want to make sure that what ever foliar fungal bio controls do not cause false positive for other tests. I know some growers who have played with Penicillin spp. And had some mixed results in Renuculus. Worth look at to. Streptomyces fruiting stalk and that fat section of the micylum looks, like aspergillosis.


Dr. James Marsden when he was there.


The basic recipe for local plant yeast collection.
Pre setup or get to know your local yeast.

Make a potato dextrose agar. (See web for recipe) enough for 100 disposable Petrie dishes. (Amazon scientific).
100 #10 fine cotton swabs sterile individually packed. Don’t try Qtips the fibers are to long.
Wax pencil or sharpie to number dishes.
Chill your agar Dishes. Two coolers red used, green for go. I duct tape, my clip board to cooler lid of red. Put your child dishes in the go cooler.

I like to collect yeast in the morning just when it light enough to work.

Swab the plant with cotton swab. Z swipe the p dish. Put in red cooler, record data.

When done put dishes in warm location 8 to 12 hours.

Use microscope and glass slides to find yeasts.

step two full boar yeast collection

I like a to uses a potato dextrose agar, plus 1 to 5 % plant extract.

This step I want 200 dishes.

This step can be a bit tricky.
I want a natural plant extract. Distilled water is my carrier.
I use 100 grams fresh plant material.
I wash is a 2% H2O2 bath for five minutes. (This May require playing with) the trick is the least amount of damage to the plant material) I am basically trying to pasteurize the plant material. Some plants my need there ends flamed to keep as little H2O2 from getting into the final product. I found a salad spinner works really well for this. Plus paper towels.

in mortar and pestle or the smallest food processor plus 1000 grams H20. To make a 10% plant and water solution.

You can check the brix of the plant solution, or a diabetic test kit to find the amount of free sugar. Ajust dextrose agar for free sugar of plant extract.

Create dishes and chill

Collect 100 dishes of yeast as above.

Incubate dish for 8 hours

Find 10 yeast colonies from your dishes and do hot wire transfer to clean plant agar dishes. Uses tight z swipe on plates.

24 hour incubation at growing temp of greenhouse minus a couple degrees C (bucket chemistry at its best)

Repeat hot transfer of colonize for a five days.


Build up of yeast.

Dextrose agar soup. See web for recipe. Plus plant extract use the same ratio as above.

Hot wire transfer yeast soup.

48 hours for incubation.



I calculate 5% solution. Yeast soup.

Dramm type sprayer. Using a super fine spray. Apply every two to four weeks.


Yeast dominance in the environment changes by the season. So I like four cultures of yeast to represent my natural yeast populations.

My business partner wanted 12. We settled on four.

Good luck.


He the food safety god. Didn’t chipotle hire way from the University.

So, back to your product.

I can see using pathogen reduction during the seasons we are tight, but I want to see data for greenhouses, preferably over a year of data.

I can see for a tight environment like warehouse production this could be a great solution.

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