White powdery mildew on squash leaves

[Rachel W]

It started with my yellow straightneck squash but I didn't know it was mildew at the time. It looked like a white liquid had dried all along the outer edge of the leaves. A week later, there are little white solid circles all over the same leaves. That squash is in the most shaded part of my garden. My spaghetti squash is in the sunniest part of my garden and about 50 feet from the yellow swish. It is now starting to get the white circles on some of the leaves as well.
Today I went to the store to get Neem oil as I had read that it worked remarkably well on this mildew. Despite calling the store first and being told they had it in stock, there were no bottles when I arrived. They said they would have more on Thursday.
Has anyone had experience with using Neem oil to get rid of mildew? Did it work? Are there any other tricks? My main focus is to be organic.
I also read that it could kill bees. If I put it on at night will the bee killing effects wear off by the time it dries up in the morning? I have counted 6 different types of bees in my garden pollinating.
Please help me stay organic!
Thanks,
Rachel

[habitat_gardener]

I've been meaning to do something about the powdery mildew on my squash leaves, so I looked at this source, which is usually reliable.
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7406.html

But I also recalled that someone at one of the community gardens was using milk to stop mildew, and I used the Cornell Formula for mildew on roses some years ago, so I googled.

This (actually more of a press release for GreenCure) says baking soda isn't a good idea
http://ncalternativecropsandorganics...xample-of.html
so if I were buying a product, this is probably what I'd try.

And since I don't use cow's milk, I looked for alternatives. One source said lactobacillus was the active ingredient. So I may try some soy yogurt, diluted to 10 percent.

Other alternatives include seaweed spray (a capful per gallon of water) or compost tea spray, both of which help activate the plant's own defenses more than they act against the mildew, as far as I know.

In any case, all of these work better at prevention than cure, or at least in the very early stages.

[LDx4]

Rachel,

I use Neem oil to prevent powdery mildew on my squash. I had lots of problems with PM in previous years, but last year and this year I've had really no problems since spraying with the Neem oil. The key is to get on a regular, weekly spray schedule, whether you see any PM evidence or not. If you can spray early in the morning, that's better, but if dusk is the only time you can do it, that would be ok. And, it doesn't seem to affect the bees around here at all - there are plenty of them around during the day to pollinate the blossoms. I can get Neem at Walmart or any of the big box stores like Lowes or Home Depot. I've also ordered it online from Amazon.

Note - once the PM is on the squash leaves, the Neem won't cure it, it only prevents it. Just cut off the leaves with the mildew and throw them away.

Lyn

[Rachel W]

Almost every single leaf has it on my yellow straightneck squash plants. Not as many on my spaghetti squash though. Howe do squash in the wild survive without getting this?!!

[RayR]

Originally Posted by Rachel W

Almost every single leaf has it on my yellow straightneck squash plants. Not as many on my spaghetti squash though. Howe do squash in the wild survive without getting this?!!

Probably because soils in the wild generally have better biological makeup than cultivated soils, therefore the plants have better resistance to common pathogens.

Here's some good information on Powdery Mildew and some controls, not comprehensive by any means, but there are some interesting ones

How to Beat Powdery Mildew

[b54red]

The diluted bleach spray works but like any thing else that stops mildew it has to be used regularly. Once leaves are well infected the bleach spray will wither them up but will not harm healthy growth or insects.

Bill

[Baja_Traveler]

I had it really bad on my squash plants this year. I sprayed undiluted white vinegar on the leaves with a hand mister and cured it up right away. Something about changing the pH drastically kills the mildew, but doesn't seem to hurt the plant any. I had to spray once every two weeks to keep it from coming back, if I forgot to, I started seeing the white haze again. Nice thing is that white vinegar is cheap and easy to find...

[Smithma]

I started seeing the same thing om my cantaloupe plants today on a couple of leaves, think I'll try the vinegar spray after it stops raining.

[bcday]

Vinegar is used by many organic gardeners as a weed killer. I strongly suggest trying it on just one or two leaves of a plant you want to keep, and waiting a day or two to see the effect before you spray the entire plant.

[RayR]

Originally Posted by bcday

Vinegar is used by many organic gardeners as a weed killer. I strongly suggest trying it on just one or two leaves of a plant you want to keep, and waiting a day or two to see the effect before you spray the entire plant.

That's good advise, 5% vinegar is not strong enough to kill most plants but for some types of plants straight 5% vinegar can be phytotoxic. It may be harmless to Curcubit leaves, but may well burn others.

[Wi-sunflower]

I just read that link Ray posted and wonder about some of it's advice. Mainly the "heat treatment" part. We had several DAYS in the 90s and that's when the Mildew actually got a big foothold on my current zucchini planting. Along with high humidity and a couple of rains, my planting may be toast now. At least that's what hubby thinks. I haven't seen it for a couple of days so I can't say if there is hope if I spray something later today.

Carol

[RayR]

Whatever you use as a control, you'll need to reapply every few days to assure good coverage of the leaves (upper and lower surfaces), and stems. it's amazing how much you miss during the first spraying.
I used Organocide 3 in 1 on my zucchini and yellow squash plants this year. That fish oil/sesame oil combo was very effective on PM.

[Wi-sunflower]

Well I don't think my plants are as bad as DH thought. We still have plenty of new growth that isn't covered with PM. So DH will be going out later with some chemical we have on hand that should help. He will also add some horticultural oil as that's also good against PM as it smothers the spores. That's also why late in the day so the plants aren't in the sun too long before dark.

I hate to give up on the zucchini just yet as it's been selling well the last couple of weeks. Since we don't have much winter squash this year, we need something that's doing well to make up the income.

Carol

[Mark0820]

I'm glad I saw this thread. I get PM on my melons every year (starts around early / mid August). I will be using Neem Oil next year, and will start the applications in the Spring. It sure would be nice not to have to deal with PM.