You might want to try 3 in 1 water and milk with a drop of dish soap

If it's mildew, it sure looks like powdery. Symptoms are very different from downy mildew. Probably wouldn't see both types of mildew together anyway since they thrive under different conditions. Downy requires wet (rain, dew, etc) and prefers cool conditions. Powdery grows best with hot conditions and high humidity, but not wetness. Also, initial symptoms of downy would likely be mostly on the undersides of leaves, normally a whitish-grey/whitish wooly growth. Lesions on uppersid eof leaves dont look like powder. Dave

I don't get "3-in-1" sprays. If you're treating one thing, you don't want to be treating the others. It reeks of laziness, of gardeners looking for a single "miracle cure" for all that ails them. Overtreating plants can cause problems rather than fixing them. What good is a pesticide doing on your powdery mildew? Apart from killing your predators?

As for powdery mildew: there are two really mild treatments for it, both peer-reviewed. One is a ~20% milk spray. The other is a 0.5%-1% baking soda spray. Some people add a little dish soap to help it adhere and coat better. Both of these are contact killers -- they kill the fungus and spores instantly wherever they hit, but only wherever they hit. You don't need to reapply after rain, but you do need to reapply weekly.

There are also a wide variety of commercial fungicides that can treat it.

It's not a deadly disease, but it is persistent and will sap energy from your plants by making them have to keep regrowing new leaves.

Oh, and as for the reason your 3-in-1 wasn't working: the fungicide it uses is sulfur. Sulfur can prevent but not treat powdery mildew; it only kills spores.

Update:

Thanks to Dave and Wally for the responses.

I took some of leaves to a horticulturist who doesn't for sure know what the cuke issues are (maybe mites or a variety of other things, but partially powdery mildew). He said the squash was definitely powdery mildew. I
got yet another organic product, Serendade, which I have heard good things about. Hopefully this will help. I couldn't find any empirical info about baking soda and milk and wanted to nip this in the bud quickly without experiementing. I am certainly open to more info about that remedy from those who have actually used it and had results...

btw to the other poster, the label on Safer 3 in 1 says it's organic, controls powdery mildew and insect pests
such as aphids, whiteflies, etc., all of which I had. It does not kill beneficial insects. I don't consider
it 'lazy' to research and use products that will deal with multiple issues.

It is really bad in NC this year for the stuff...one of the worst I've seen in a while.

I have used the baking soda, water, and a little liquid soap on my squash and cucumbers, and has worked very well. As someone mentioned, you should reapply every week.

Not sure of how you are watering the plants, but with my plants I have learned that watering in the evening increases powdery mildew a lot. So try to stick to watering early in the morning if possible. The best watering method is using soaker hoses or some other watering method that is not overhead watering. The biggest thing is to avoid getting the leaves wet as much as possible.

Good luck with your squash and cukes,

Tee

The link has a recipe for the baking soda spray along with a few others.

Here is a link that might be useful: 12 remedies for the garden

Thanks Tee! I used the Serendade on the foliage this evening, and hope it helps with the PM. But I watered last evening! I did use the soaker hose though. Good tip to water in the morning in the future.

Lost one of the squash today to SVB....it was so fast I could barely believe it! There is one stalk left on the plant (when I last looked, anyway), and I discarded the rest. It's so sad to lose a plant when one has such a small garden... :(

He said the squash was definitely powdery mildew. I
got yet another organic product, Serendade, which I have heard good things about.

Haven't seen as much research or anecdotal evidence on it, so I'd be interested in hearing your results with it.

Hopefully this will help. I couldn't find any empirical info about baking soda and milk

Do you want peer-reviewed or anecdotal? As mentioned, I've run into ample peer-reviewed, and can give you links for that if you want. I can also attest to it myself. I used to get it every year, horrible infection, until I started using the baking soda spray.

btw to the other poster, the label on Safer 3 in 1 says it's organic, controls powdery mildew and insect pests
such as aphids, whiteflies, etc., all of which I had.

1) "Organic" does not mean good, and "Synthetic" does not mean bad. Rotenone is produced from the roots and stems of lancepods, and not only will kill your ladybugs and bees, like most broad-spectrums, but it's also suspected of contributing to Parkinsons. By contrast, acetamiprid -- a synthetic -- is by all standards far safer to people (although is still broad-spectrum).

2) There are actually two completely different types of Safer 3-in-1. There's the bottle version and the concentrate version. The bottle version is sulfur and soap. The concentrate is sulfur and neem. Neem is a broad-spectrum; it *will* kill your beneficials. Soap varies; it'll kill ladybug larvae but not adults, and won't hurt parasitic wasps and lacewings.

The baking soda without the milk would probably work (and does for me) just as well. It's something you need to apply every 5-7 days, though, and still isn't some magic bullet.

You don't want to use a heavy concentration of it (as mentioned above) because it'll burn through a leaf if mixed in too heavy a concentrations.

Enough people use a baking soda/water (sometimes detergent or milk, too) that the right mixture/amount you can make your own educated guess.

I should mention that you really should add an horticulture oil or detergent with the baking soda for best control, but generally I am working with 2-3 plants at most that are susceptible to PM. I can spot treat them very quickly between regular spraying.

...and for anything climbing or in the wind a lot (some cukes/melons/etc) you might want to add some horticultural oil or detergent to help it "stick" a bit. That helps a lot where the wind and gravity will play with how it sits on the leaves.

The oil is a lot more effective than a detergent, but it all comes down to how vigilant you want to be...time/effort vs. cost.