Powdery Mold! A few questions...

I posted this in another thread, and instead of hijacking the other....

Here's a weird one: My 2 grow rooms(one veg/one flower) were very infested with PM. I took Water/Baking Soda and Milk and mixed in a sprayer( about a gallon ), and sprayed the living piss out of everything!! I have some in Flower wk-6 that had it on the leaves and sugar leaves, but not stems, so I soaked all of 'em. I can't find any more spots, but now everything is white from the heavy bicarb(baking soda).

Should I spray the white dust left from yesterday's treatment off with water?

The weird part is: both of my rooms stay at about 11% humidity and I've used clones from one source from the get-go. Nothing that would make me even begin to think about any type of mold or mildew! So, where in the world did this come from. I live in Maine and it's still well-below freezing at night and there's still a couple feet of snow on the ground, in my yard. Any ideas?


Is there anything else I can do to help save my buds(which look and smell just fine, at this time), besides spraying/wiping them down until harvest?

PM likes it cold and wet.
Check temps and humidity, especially in night cycle.

Increase grow room heat .
Add fans.
Thin lower or unneeded foliage ( air flow ).
Don't mix milk with baking soda ( you can suffocate leaves )
Personally I would wash that crap off, raise the heat , thin it out and increase fans.

PM is everywhere...and I mean everywhere,.it's only when the plant is stressed does to it show up. Too low humidity is stress.

Foilar spraying during flower just makes it worse. If you must continue just blow dry them with fans and return to room. ( Speaking of which...clean..clean..)

First of all, I misnamed this thread. It should read "Powdery Mildew", not mold.


I have 2 humidity meters in thew rooms and had them attached to the wall. They both read 11% humidity. The temps are above 70 F, and actually more like 75-78 in light cycle.

I put the meters on the floors and the humidity has gone up to 12% in 8 hours. Temp is same.
I'll check again during the lights-out cycle tonight. This is Maine, so...

I saw this product:https://www.hydroponics.net/i/101011

and this video:
I plan to clean the rooms, defoliate as much as possible, and I'm in the market for a couple more fans(right now, I have 1 oscillating fan, about waist height in veg room and three fans(1 stationary & 2 oscillating) in flower room that are low positioned).

Also, I have been doing the spraying/defoliating within the rooms and I sprayed that stuff all over the floors and walls, as I assume an alkaline environment works to stop the spread of spores, but does not kill them.

Sleepybud said:

They both read 11% humidity. The temps are above 70 F, and actually more like 75-78 in light cycle.

Click to expand...

It's a common misconception that it's high humidity that leads to infection of PM. PM does not need water to be able to infect. It's more common to get infected in hot an dry environments and not cold and wet like a previous poster claimed. The germination of the spores however does require high humidity, to be able to spread and show up as fast as it can, but infection itself not a result of high humidity. In fact, as long as the leaves are wet, like in the rain or when sprayed very often, the plants don't get infected (also opposed to popular believe)... they can get bud rot instead but that's besides the point... This late in flowering there's not much you can do. Don't feed high N. If you still have healthy fans you could try some neem oil.

11% humidity is obviously during light on, your problem is possibly caused by condensation from the day/night temp fluctuations.

A very common cause for spreading PM is insufficient ventilation, recirculating air instead of blowing it outside.

Also, I have a humidity meter on the wall too, and one amongst the plants. The difference can be quite large especially when the light (my hps) hits it directly. If that 11% would be correct your plants are not doing much either, that dry will cause the stomata close to reduce transpiration to prevent drying out. If the meters are in the light directly, cover them with something, put them in the shade.

I just checked up-close with a scope and I can see residue left from the baking soda solution, but isn't that a good thing? I mean, the leaves are looking up and not drooping. Isn't an alkaline environment what I'm looking for?

It is quite dry..

Last night before lights out, with my humidity/temp gauges on the floor in the shade: Humidity- 16%, Temp- 68

Early this morning, before lights on:
Humidity- 19%, Temp- 65

I sprayed everything with water to rinse off the caked-on baking soda.

I removed everything from the rooms, bleached floors and walls, and increased fans.

Presently, everything looks good. Plants look happy! I see spots where the mildew was, but see no active mildew at this time. I've got my bleach/water spray bottle ready if it rears it's ugly head again!

It seems the super-alkaline solution was a good idea.

Sleepybud said:

Last night before lights out, with my humidity/temp gauges on the floor in the shade: Humidity- 16%, Temp- 68

Early this morning, before lights on:
Humidity- 19%, Temp- 65

I sprayed everything with water to rinse off the caked-on baking soda.

I removed everything from the rooms, bleached floors and walls, and increased fans.

Presently, everything looks good. Plants look happy! I see spots where the mildew was, but see no active mildew at this time. I've got my bleach/water spray bottle ready if it rears it's ugly head again!

It seems the super-alkaline solution was a good idea.

Click to expand...

This is a good start but if anything you need to raise your humidity, too low and your plants will essentially suffocate. As Sativied pointed out, there is an internet myth that claims high humidity causes it, that's a total myth and gets passed on by those who have never experienced PM. Air flow will definitely help, the more the better. Light defoliation, and by this I don't mean stripping all your leaves off, I mean very selective where there are multiple leaves on top of each other/touching, that's the prime breeding place for PM. The most likely place it started from was either a clone you brought into the room that already had PM, or where I originally got it, bringing in outside air. If you're brining in outside air and your area has PM, filter it with a good carbon filter or it will continue to infest your room.

All that said, I have PM in my area (outside) which destroys certain bush types every year. It's everywhere. It's impossible to control or eliminate the source, so all you can do is manage it in this scenario. This time of year (spring, cool temps but everything thawing out) is the worst. In order to manage it longer term:
1) Identify the source of PM. This can help reduce the chance of brining it into the room
2) Get yourself a good HEPA filter/air cleaner, doesn't eliminate it but definitely helps and reduces the chance of it getting started on your plants
3) Maintain normal ranges for humidity, too low is as bad as too high (e.g. 35-50% is good)
4) Clean well in between runs including (diluted) bleaching of all surfaces

If you find it to be persistent (most times if you have it it's because it's rampant OUTSIDE in your area):
5) Use that baking soda mixture (+a couple of drops of dish soap, a few drops of olive oil) you mentioned but no milk unless it's raw milk, in that case either use one or the other, not both combined. Don't overdo the baking soda 1/4 tspn per litre of water is sufficient (1 heaping tspn per US gallon) or it will burn the shit out of your pistils in flowering
6) Spray religiously every 2 weeks, throughout veg and flower. It works great, but it wears off within 10-14 days. Either spray in the room, then dry up any over-spray/dripping, turn your light off before spraying, crank all fans to highest setting and allow it to dry for a couple of hours before you turn your lights back on. Or spray outside the room with dim lighting and dry before putting back into the room.
7) Look for strains/phenos that are more resistant to PM/Mould. Sativas or sat-leaning strains tend to be more resistant ime, particularly those with high levels of limonene but I've found a couple of Indica or indica-dom's that have PM resistance. I've found even certain phenos of the same strain to be resistant and a "sister" right next to it with signs of PM. Any signs of PM and I cull immediately and try another strain or pheno. If the strain/pheno is subject to getting PM, there is no way to manage it, just cull it and move on.

Learn to identify it early as once it hits where it's obvious/noticeable it's probably not something you want to smoke. Do one of those peroxide baths after harvest to clean them, then make hash or oil out of it. It's a pain in the ass but like anything else, it can be managed. Good luck.

Thanks for the response!

Clean Clean Clean Your Bleach and water will do the trick PM can get on your shoes, hands clothing, go into your room clean and don't let anyone in there either. I have heard a buddy used this and got rid of there Problem with PM, It will also work with Spider mites. 1tbs of Dawn 1Tbs of canola Oil and right before you spray them add 1Tbs or Rubbing Alcohol to 1 gallon of water spray under leafs and outer till dripping. It should take care of your PM and SM if you have them too. GL Hope you get er gone. Happy Grow

Thanks again to all the great responses!

You gents have opened my eyes to more! I seem to never stop learning about this. Complacency has no place in a garden! I've really got to pay, even closer attention!

I've changed things here and will keep my eyes peeled. I have forest right outside of my back door, so it seems that if there's something that grows outside(good or bad), it'll find its way into my house, hitching a ride either on me or my dog. I did store things in my room, as it there before it was a grow-room, but everything is cleared out and bleached.

Right now, it looks a bit dusty still from the baking soda, and I rinsed the buds again(with water and fans-a-crankin') and besides some of the dead spots on some leaves, they look fine! Hoping I caught it before it was too bad!

SB