The first published study I want to look at came out in 2020 and it compared many of the most common methods of Powdery Mildew remediation against each other in one big side-by-side trial.
This is a bit like the Tour de France, or maybe the Olympics of powdery mildew killing.
Evaluation of disease management approaches for powdery mildew on Cannabis sativa L.
In this study, they compared different commercially available treatments for efficacy against the fungus in ways I’ve never seen tested before.
The 9 contenders in this arena of gladiators were many of the old favorites, but also a few new faces that haven’t been around so long.
When you look at the graphs below, notice that the higher you get above zero, the worse the treatment worked, so pay attention to those that go below the “Disease Rating” of 5.
The one product named Luna is a strong man made chemical fungicide that is approved for use on many food crops but not on cannabis. By adding it to this test they gave us somewhat of a baseline to compare the other products against. The Luna product was only sprayed one time at the beginning of the trial whereas the others were applied weekly.
The Results!
The clear winners are Neem, MilStop and Regalia.
I was not surprised to see Neem and MilStop performing right up there with the best. However, the performance of Regalia is a bit of a surprise to me even though I knew it boosts immunity, I still had no idea it could compete so evenly with Neem and MilStop.
Among the biological products, Bacillus subtilis (Rhapsody and Cease) came in as the strong winner of the three species looked at in the study.
The non-traditional contender Orthosilicic acid (Silamol and others) put in a very solid performance that only followed slightly behind the top three.
Drop down each tab to read more
MilStop from BioWorks Inc. is an EPA-registered, potassium bicarbonate based, broad-spectrum foliar fungicide for curative control of powdery mildew and preventative control of many other foliar diseases.
Curative control of powdery mildews:
A potassium bicarbonate-based, foliar fungicide that kills powdery mildew on contact by pulling water from spores and their growing strands. It also inhibits enzymes involved in fungal cell wall penetration by altering the pH on the leaf surface.
Can be used in combination with other foliar disease control solutions
Fully dissolves in water; dries quick and clean
Neem is one of the oldest and most loved farm problem solvers known to man. Neem kills or repels insects, mites and fungus so well that many years ago it became the go-to product for pretty much anything that bothers your plants, and the fact that it doesn’t kill beneficials and has never been shown to be harmful to people just rounds out Mother Natures perfect creation.
This study proves once again, that Neem is the king of organic IPM tools.
Which Neem product should you buy??
There are many plain cold pressed options available and they all work the same. These standard versions of Neem require the addition of an emulsifier and they can be pretty hard on your sprayer if you don’t clean it carefully after use.
The only real “stand-outs” among commercial Neem product offerings are Rango and TerraNeem EC from Terramera. Both products contain built in emulsifiers and are OMRI rated. Rango is a micronized solution that performs quite a bit better than normal Neem because the droplets are so tiny they can penetrate inside small creatures very easily.
Neem products can safely be combined with most other IPM products – except Sulfur.
1x weekly applications are a great baseline preventive IPM strategy for times when you don’t have any problems, but I’ve also applied 3x per week to knock down a heavy infestation of PM or Aphids.
I also like to combine Rango with either Pyrethrin or Azadirachtin for an even stronger slapdown on a bug population.
I honestly can’t recommend these products enough.
Procidic is a broad-spectrum foliar spray (bactericide and fungicide) that eliminates pathogenic fungi and bacteria using Citric Acid as an active ingredient. This exceptional organic product works on contact, but is also absorbed and rapidly becomes systemic in the plant where it stimulates the production of phytoalexins (a plant’s natural defense against microbial attacks), which inhibits the future growth of fungi and bacteria.
Benefits of Procidic:
- Can be used in all stages of plant growth
- Controls the most common fungal and bacterial diseases in plants
- Now OMRI Listed and WSDA certified for use in organic production
- No re-entry waiting period (0-hour REI) and can be used up until the day of harvest (0-day PHI).
- Highly flexible – can be mixed with foliar feed or other IPM products.
Controls: Powdery Mildew, Aerial Fusarium, Altenaria sp, Anthracnose Pseudomonas, Downy Mildew, Erwinia sp, Fusarium Wilt, Botrytis cinerea, Phytopthora sp, Pseudomonas, Verticillium sp and many others.
This biofungicide ignites the natural defenses of a plant to protect it from a variety of foliar and soil-borne fungal and bacterial diseases. Its active ingredient is the extract of Giant Knotweed (Reynoutria sachalinensis), which stimulates plant vigor and growth by significantly increasing chlorophyll concentration in the plants. The extract also stimulates the plant’s ability to develop resistance to plant pathogens (systemic induced resistance). This resistance builds plant health as opposed to attacking the disease directly.
REGALIA should be applied early on, as a preventive application instead of a curative treatment. This will provide protection for sprouting leaf tissue, flowers, above ground fruit and vegetables. Applying REGALIA to an actively growing plant will keep the plant protected from certain plant diseases, particularly those that affect plants in early development.
This product can also be applied as a soil drench where it stimulates resistance to soil pathogen when it comes in contact with the roots.
Effective against:
- Powdery mildew
- Botrytis
- Pythium
- Verticillium wilt
- Alternaria fruit rot
- Anthracnose
- Black spot
- Crown rot
- Phytophthora
- Rhizoctonia
- Wilsonomyces carpophilus (shot hole disease)
No chemical residue.
2 tbsp./gal. of water
(containing Bacillus subtilis strain QST 713)
Active Ingredients
- Hydrogen Peroxide H2O2
- Peroxyacetic acid CH3CO3H
OMRI Listed
ZeroTol 2.0 controls the following pathogens…
Algae, Alternaria, Anthracnose, Aphanomyces, Bacterial spots and rots, Botrytis (grey mold), Downy mildew, Erwinia, Fusarium (root rot), Leaf spot, Phytophthora (blights, rots), Plasmopara, Powdery mildew, Pseudomonas, Pythium, Rhizoctonia, Rust, Scab, Smut, Thielaviopsis, Uncinula (powdery mildew), Xanthomonas, Wilts and blights, Ralstonia solanacearum (brown rot, bacterial wilt), Sclerotinia sclerotiorum (white mold), Tobacco mosaic
This product has the benefit of breaking down into harmless chemicals, hydrogen peroxide (H2O2), and Vinegar (CH3COOH) which will almost completely evaporate within a matter of hours. Note that the formula for both ingredients is mostly Hydrogen and Oxygen with a small amount of carbon left over after evaporation – definitely nothing to worry about.
ZeroTol 2.0 is rated for use on cannabis up to day of harvest and even in post harvest decontamination.
ZeroTol 2.0 is a broad spectrum Algaecide / Bactericide / Fungicide
Provides immediate on-contact activity with no harmful residues making it ideal for use in integrated management programs to combat pesticide resistance up to the day of harvest.
Orthosilicic acid
The efficacy of UV-C light to manage powdery mildew was also examined by daily exposure of leaves using a handheld device from CleanLight Pro UV-C https://usacleanlightdirect.com/cleanlight-pro
The susceptibility of 12 strains (genotypes) of cannabis to disease development was assessed to determine their resistance to powdery mildew.
Now that you’ve got a great list of products, let’s look at how to go about using them on your farm.
Prevention
Setting yourself up for success starts before you fail.
If you take the proper steps to prevent powdery mildew, it is possible to go through most of your time without ever seeing it in your farm.
Here’s how it’s done.
Environmental Control
All fungus species are adapted to live within a very small range of optimal conditions and anything outside that range makes them scarce.
So what does Powdery Mildew need to find before it will set up camp in your farm?
Temps in the range from 60 – 70 F, or 18 – 21 C.
Relative humidity in the range of 60% or more.
Low air circulation
Low light conditions
- Night temps in the low 60’s F with relative humidity 93-99%
- Day temps in the 80’s F with relative humidity 40-70%
Remediation
Once you spot a couple little fuzzy spots on a leaf, what are you gonna do about it?
CleanLight Pro UV-C
https://usacleanlightdirect.com/cleanlight-pro
This product is a big light with a protective cover which directs the harmful light away from the human user. This is a mildly dangerous thing to do but if you wear the proper goggles, and don’t allow any exposed skin, this product is HIGHLY effective. The fact that there is no chemical involved is a plus for many growers in highly regulated areas. The drawback is that the light must come in direct contact with the mildew so you have to move the light fixture through the plants quite a lot and very slowly.
Early in the crop cycle, Milstop, Neem and Regalia are equally highly effective even when applied only once per week and I’ve personally used Neem 3x per week with even better results. These three products are not exclusive of each other so in the real world you can rotate by spraying one of these three products every other day for a period of two weeks.
Late in the crop cycle there is even more desire to keep any sort of chemical out of the flowers. ZeroTol was moderately successful at 1x per week in this test but you can easily up that dose to 3x per week for a very thorough kill rate.
Defoliation. In early plant growth stages you can remove roughly 20% of the leaves without harming yield. Late in the season (end of week 6 and beyond) you can remove 70-90% of the leaves to control mildew and also to make it far more likely that your other treatments (listed above) will actually reach all infected places on the plant.
If you’re looking for some professional help with IPM problems, reach out to my friend Matthew Gates at Zenthanol.com