Powdery mildew or something else?

Hi everyone. So I’ve had this white stuff appear that I’m concerned is powdery mildew. Here’s why I’m not SURE it’s powdery mildew:

  1. I have three autoflowers: northern lights, amnesia haze, and blueberry OG. All three of them are about 9 weeks old and are RIGHT next to each other (I only staggered them a little the day before yesterday and before that their leaves were touching). The northern lights is the only one NOT flowering yet. Even though the three were right next to each other/touching, the amnesia haze is the only plant showing symptoms.

  2. the pattern of the potential mildew is strange. Rather than it looking like it’s starting to grow in places, it looks more like something dripped, dried, and left a residue. Meaning there was a fat drop of some type of moisture that then dripped onto some leaves below (look at the pictures and let me know if you see what I mean). Additionally, they used to get foliar feedings of calmag and neem oil for pests. But since they’ve been flowering, I haven’t foliar fed them anything so it’s been weeks. I don’t know if this is just old, old residue from those times that never fully cleaned off and maybe collected other stuff in the process?

  3. I am most definitely suffering from glassy winged sharpshooters. These annoying little buggers eat my beautiful plants and will then secrete and spew out this moisture that then leaves a white residue on the leaves (which kind of looks like powdery mildew). From time to time, I’ll check the plants and find these random drips of “water” in random places on the plants. I’ve also seen them shaking off the “water” off of themselves, and it’s a surprising amount, so there are sometimes fat drops and smaller drops scattered about. I’ve wondered if this might be leavings from them. However, I’ve only seen the sharpshooters on my autoflowers I think once, maybe twice (though that doesn’t mean they don’t go there). I’m constantly finding them on my photoperiods. Since I don’t see them on the autos as often, I’m not 100% confident this white stuff is from them.

So what does anyone think? Is this powdery mildew? Sharpshooter secretions? Something else? It looks like a super thick layer of frost but I don’t know if the frost that shows up during flowering gets to be this thick. What does anyone think it is and what should I do?

Here are the specifics and some pictures:

Strain: amnesia haze

Type: autoflower

Climate: outdoor

Grow medium: fox farm Ocean Forest soil in 5 gal pots—small percentage of worm castings

pH: they’re due for another check but last I checked was around 6

Nutrient strength: not sure but I’ve been using ILGM’s Flowertime Fertilizer and Plant Booster once a week as directed (yesterday the ones that are flowering got flowertime and their second dosage of plant booster)

Light type: natural sunlight

Temperature: it’s been in the high 80s-90s this past week

Humidity: can’t speak for always, but it’s been humid here in Southern California. At the time of typing this it’s supposedly 93F with 31% humidity

Ventilation: natural air

I can take more pictures if needed. Thank you for any and all help!


@AAA @Myfriendis410

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Well, seems you have reasons it could not be powdery mildew, so it’s hard to say.

Whatever it is, straight H202 sprayed on it will kill/remove it.

Thats my best advice.


Thank you for responding! Is it still ok to spray on my plants even though they’re flowering?

Looks like something dripped on it. But easy to treat regardless: put some 3% peroxide in a spray bottle straight and spray the spot. It will likely clean it off and if it is WPM then it will nuke it. Won’t hurt the plant a bit.


Yes, alcohol is the one you can’t use on a flowering plant, melts the trichs.


Powdery mildew for sure I had to beat it back also. I would highly advise to spray the entire plant. It takes nothing for this stuff to spread


Spray JUST peroxide? Not a peroxide/water mixture?

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Straight peroxide works fine. 50/50 works too. Just dilute it with distilled water so it doesn’t lose efficacy.


Soooo I sprayed my plants with 3% H2O2 on the potential powdery mildew spots. At this point, I’m pretty confident that it’s from the glassy-winged sharpshooters and isn’t WPM, but the white spots didn’t go away and now the leaves are looking seriously damaged with all of these brown spots. Does anyone know what’s going on and what I should do? (Note: the yellow leaf was starting to yellow already but it’s the way it yellowed and all that)

Did you spray during day light? It’ll easily burn the plant. The drops act as magnifying glasses.

Hey there! Nope, definitely did not. I sprayed it at sundown. Unless it pooled and collected there into the next day? But it’s been pretty warm so I guess I’d be surprised if it did that. Is that what sunburns look like?

I’ve had spots like that after spraying with h2o2. Even after sunset.
New growth should be fine.

The lower yellowing leaves aren’t too big a deal.

Hi everyone. Another question….I know, right?? Is this powdery mildew?