Does Neem Oil Cure Powdery Mildew?

alrightypewriter(9b)July 29, 2009

Some of my squash leaves have powdery mildew. It's not so bad that the entire leaf is white but there are definitely white spots here and there. How serious is powdery mildew and can Neem Oil cure it rather than just prevent it?

I have been spraying Neem once a week for bugs so I was surprised by the powdery mildew. It's mostly on the lower leaves that are shaded.

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anney(Georgia 8)

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

    Bookmark   July 29, 2009 at 6:00PM
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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!


    Bookmark   July 29, 2009 at 8:12PM
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bella_trix(z6b SE PA)

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.


    Bookmark   July 29, 2009 at 8:21PM
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lolear(5b - Chicago)

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.

    Bookmark   July 29, 2009 at 8:43PM
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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.

    Bookmark   July 29, 2009 at 8:54PM
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Neem oil works great. I had a problem with black spots with my roses. It was covered in mildew and aphids. I drenched the thing in neem oil spray a couple of times and it's doing great now. The first person is wrong. It is a fungicide AND a pesticide.

    Bookmark   May 26, 2010 at 10:17PM
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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.

    Bookmark   July 16, 2010 at 2:56PM
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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".

    Bookmark   July 16, 2010 at 10:08PM
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rhizo_1 (North AL) zone 7

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.

    Bookmark   July 17, 2010 at 12:33AM
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For those who keep saying Neem is not a 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

    Bookmark   August 7, 2010 at 10:08AM
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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.

    Bookmark   January 17, 2011 at 7:30PM
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