No, Neem Oil doesn't affect funguses. It's a pesticide.

I too have that dastardly fungus on my squash plants. I've had good luck with spraying an organic spray that has copper in it. Don't recall the brand. My local Southern States Farm Supply had loads of it.

I read how folks have had good luck with spraying 1 part milk to 9 parts water. That doesn't seem to work for me.

Each weekend I cut the really infected leaves away. Good news is my squash plants replace the cut away leaves very quickly with healthy ones.

That fungus will definitely kill the plant. Keep after it.

Good luck!

Erin

I have good luck with milk, but I use it at 1:3, 1:4. Some squash varieties handle powdery mildew better than others. My favorite new squash seems really susceptible. I'm guessing it would do well in a drought.

Bellatrix

Last weekend I noticed mildew on the leaves of my squash plant also. I have a product called green light and it contains neem oil. I used this on the squash and the mildew went away. Since powdery mildew is a kind of fungus, and the product claims to be not only an insecticide but also a fungicide and miticide, I suppose it is an appropriate treatment. Don't know if this applies only to the green light product (it does contain other organic ingredients) or all neem. Seems to have worked for me, though.

Neem oil is not a ONE SHOT cure for PM. You have to keep spraying. I am using a product, made by OMR(?) that hs 73% neem and the rest not revealed. I mix 2 TBLS per galloon.
It gets rid of PM, where sprayed. But then PM appears on other leaves. You have to keep doing it as long as and as often as necessary. Because it is a natural oil, it has no side effects on the plants. Just keep spraying wherever and whenever you find PM. 5 days wait is too long.

There is a chemical sprayer called "Immunex" wich claimed to boost plants immune sytem and fight PM. But it comes as diluted spray and it is expensive.
The milk formula, I have heard should be One part milk and three parts chlorine free water plus a tespoon of baking power per half a gallon. I would give a try. Supposedly the bacterial action of milk and baking soda kills powder mildew.

Neem is not a fungicide. It does not affect fungus in any way.

What neem does is coat the leaves (and the fungus on it). Healthy leaves that are coated are protected against fungus and fungus already present on the leaves gets coated so it cannot breathe or get wet and it cannot reproduce, so it eventually dies.

Neem can be used to prevent mildew from getting established and it can also be used to prevent it from spreading and to eventually "choke" it.

I am getting good results using neem oil in a potassium soap carrier (Enviro Neem) at a rate of 0.5%, mixed with a bit of liquid seaweed emulsion. I'm using this on peas & calendula (it's cool season here Downunder) however I would not say that it eradicates the PM.

I think viktoria is on the money about the mechanism of how this works (plus the seaweed is supposed to alter the pH on the leaf surface to make it less hospitable to the fungus).

But as cyrus_gardener says, you have to keep spraying because IME the PM does tend to keep cropping up in new places, especially while environmental conditions are favourable or the plants are stressed/getting toward the end of their life. Once PM appears the neem spray is more of a controlling or delaying tactic than a complete "cure".

Neem oil is recommended for a number of fungal disorders. It has very good fungicidal properties, both in prevention and curative . I strongly recommend it for PM and for black spot, as those are the only things that I have occasional problems with. It's also recommended for some blights, downy mildew, alternaria, and rust diseases.

Be sure to get the right kind of neem. And know that any fungicidal product should be used in conjunction with the kind of horticultural practices that prevent a disease outbreak in the first place, or that mitigate a problem when it occurs.

For those who keep saying Neem is not a fungicide...do some Googling cause it is: "A broad spectrum insecticide, miticide and fungicide."

I used Rodales info and made a garlic spray. It didn't work. I tried milk last year. It didn't work. I just neem oil this morning. We shall see.

I've read sodium barcarbonate works well too. The plants' leaves are acidic and the SB makes it more alkaline so they can't thrive.

Good Luck. I have the prob. too!

Here is a link that might be useful: Neem Oil Info

I found some good information here. I would offer this thought up about neem oil use for prevention of powdery mildew, think of it more of a fungistat then fungicide. But neem oil is both. Powdery mildew is almost impossible to rid from garden crops as spore floats and is not killed unless treated with good Fungicide and contacts all spores. One spore left, and the rest of the story is just maintaining mildew from taking over garden crop. Hydrogen Peroxide 3% also works in pinch if you need something safe to knock back the mildew from good growing tips or fruit that might be near foliage that is infected. Mix 2-4 tablespoons per pint.

I dont have any squash plants. My gardenia however had the beginnings of powdery mildew. I sprayed it with a small water bottle with a few tablespoons of neem and it was gone on contact. I'm very pleased.

1. I had a bad infestation of PM and aphids. A good drenching of diluted cold pressed neem oil and soap took care of it immediately!!! Funny thing is, I first sprayed a ready to use store bought product (Garden Safe) the day before and it didn't do a thing on PM or aphids. The cold pressed concentrated neem did the trick. I mixed it with some natural soap and water.

Powdery mildew is one of the few fungi that grows better when it's dry rather than damp. Hose the leaves off in the morning.

Neem is an excellent fungicide so feel free to ignore comments by those who just don't know much about its attributes :-) But like the vast majority of any commercial fungicides, it is not curative but only preventative. You need to spray before you see any symptoms. Spraying after the PM becomes obvious will only help to control the spread to any unaffected foliage but it will not 'clean up' what is already present.

And the above comment about spraying or hosing down the foliage is on point. PM spores are unable to live in a moist environment or when wet.

btw, the product 'Rose Defense' (by Green LIght) was forumated specifically to help control a number of rose fungal issues - PM, rust and black spot - and is clarified hydrophobic extract of neem oil. This was my first intro to neem oil many years ago and I can testify to its effectiveness.