I posted a bunch in the past about PM but since this is a sticky I stuck some of the stuff together in this one post. There is some good stuff here.
I really like using silicon ALL the time, from day one add a bit to the resevoirs and maybe you can avoid catching it in the first place. Its really easy, cheap, and is a nutrient anyways.
The challenge is killing the asexual spores called conidia. These are the white "mildew" that is seen. PM also has sexual spores that it releases when it gets cold and it thinks winter is approaching. I think these are called cleistotheca and are little brown sap looking things on leaves that look like thrip turds. The conidia I read can live up to 21 days, the Cleistotheca live months. I think if you have mildew it is better to up the cold nights so that u only have conidia to fight against. These conida are asexual spores that need to live on another plant. They are obligate parasites. In nature they might get blown by the wind into atmosphere when conditions good and land far away and start to grow. In a room they might land on walls or any surface like edges of tables, under tables etc. I have yet to find out if conidia or cleistos can rest in medium and grow onto root for example. But so the spores are on the walls. How to kill them? You can turn off everything for 3 weeks which hopefully the spores will have died. But u do not want to have everything down that long so how can we accelerate this shut down? I think the variables and products might include Sulfur Burners, Ozone Gnerators, high temps and maybe other stuff too.
I just read a book called Hemp Diseases and Pests by MacPArtland, Clarke and Watson. It is very comprehensive and one guy is a college professor. Serious people should but it, it costs ~175 but worth it. On page 11 they mention PM. There are TWO species that infect cannabis; Sphaerotheca macularis and Leveillula taurica. Knowing these two names means interested people can research google these names and get lots of SPECIFIC information. One tidbit of interest is that the relative humidity for each for germination is different. L taurica conidia can germinate with 0% RH and optimal growth is 25C (77F). In contrast, S. macularis conidia germinate best at 100%RH with optimal growth at 15-20C (59-68). So perhaps the experience and advice that one might have could depend on the species you r experienced with and that is hard to know. L taurica likes it warm and dry whereas S macularis likes cool and wet. I supose there are some conditions that are bad for both. S macularis infects hops which is similar to cannabis.
Here is a brutal story; Hops used to be grown around New York, about 70 years ago PM infected the field and annihilated them. Not sure which strain, perhaps s macularis. The whole hops industry shut down and all hops growing moved to Washington state where this PM strain did not exist until about 2002 when it started showing up Outdoors, throught the last 100 years, PM often is so hartd to fight the whole industry will just move when possible. Now all the hops is fumigated and grown like grapes with lots of sulfur. The entire wine grape industry in USA uses Fumigants like Supher. Without them there would literally be no wine industry!
Pro-Tekt Silicon might be able to help against PM
Fighting this Borg is tough. I read some articles by greehouse people about silicon being used to toughen up plants. Dyna Gro makes it and lots of people use it, i think more for heat tolerance but it might be good for PM. Barricade also is Silicon. It will not eradicate it, it might control or mitigate it. It might makes leaf cells thinker. Below is an article from a recent legit journal. Any thoughts? Anybody use this? I recommend using it proactively as a normal fertilizer element BEFORE getting exposed to PM. Then u may never get PM!
Abstract Foliar and root applications of different silicon (Si)-based formulations were evaluated for their effects in reducing powdery mildew and promoting growth of wheat plants. X-ray microanalyses of treated plants revealed that root applications resulted in consistent deposition of Si in the leaves. In terms of powdery mildew control, root applications at 1.7 mM Si gave consistently the best results, reducing disease severity by as much as 80%, regardless of the product used. Although less effective than root applications, foliar treatments with both Si and nutrient salt solutions led to a significant reduction of powdery mildew on wheat plants. This suggests a direct effect of the products on powdery mildew rather than one mediated by the plant as in the case of root amendments. In our experiments, Si amendment, either through the roots or the leaves, did not increase plant growth. These results lead to the conclusion that Si is primarily, if not exclusively, absorbed by the root system and that such absorption by the roots is necessary for an optimal prophylactic effect.
I came up with a concept of infection that I will delineate now so that we can have a baseline for what infection is.
Level 0 (zero) infection: is actually NO infection. There are absolutely NO PM fungal bodies, mycellium, hyphae living anywhere in the system. This is primarily in a greenhouse or closed environment.
Level 1 infection: Low level infection. Under control. Rarely see patches but they do not really progress. Control might be natural immunity, resistance, neem oil, serenade. This is the natural state outdoors where spores might land on plants and not progress or might only get bad if weather changes. This is the state that many growers are in. They say they do not have mildew but really have a latent infection. If they give away clone that look ok the giftee gets PM. If they change the temp/humidity/environment then it shows up leading these people to say PM is always there and only conditions prevent it.
Level 2 infection: Full blown infection. Everything is being annihilated by PM. Trillions of spores. Might be using sulfur burner every week or two here to keep down infection, but stop and soon - WHAM.
I will try to use this nomenclature from here on sincce I think many people are in level 1 infection and think they are in level 0. An analogy is Herpes. Some people have cold sores all the time (level 2), many people have occasional outbreaks or even almost never (level 1), while some people do not have it and this can be proved by a negative antibody test (level 0).
I like to be at Level 0. Level 2 is unacceptable. Level 1 is an interesting place. Might plants that are really treated wtih proper control regimen and fresh vegeative plants revert to level 1????
The person I spoke with today said that Serenade applied weekly to level 1 plants might eradicate PM. The way that I have gone from Level 1 or 2 to level 0 is by shutting down as I mention above.
Link to article on greenhouse L taurica
Of note is that in peppers here they take 21 days to grow and seem to have spores on underside of leaves.
Link to S macularis on hops