I've had a terrible time here in L.A.- zone 10- with powdery mildew - this time it got my squash, cucumbers, tomatoes and bush beans; now it's working on my pumpkins. I have tried a bunch of things - milk, baking soda and a little detergent, etc.- but they seem not to work. Realize I probably water too late in the day and put manure on at the wrong time...but still! Most sites states that "treating the soil" is not useful, but one site says to cover with clear plastic and let it sit for 4-6 weeks - longer if it's rainy. Seems like a long time to wait - but I'd do anything to fix this problem! Can anyone help? Another thing - I'm from the South and can't help but notice how much better plants like melons, okra, summer squashes do there. I'd attribute this to it nearly always dropping down to the 50's and 60's at night, instead of staying hot. Am I the only one that thinks this?

@gardengal48 (PNW Z8/9) I have made a lot of progress with this hedge, from its prior sorry state. Compost as a mulch made big changes, and then I discovered they were short on water so I added a manual drip line and do a weekly drench outside of the normal irrigation schedule. These changes resulted in fewer leaves showing signs of fungal infection, and dramatically increased growth of new leaves. Everything was going well, and as usual, a new disease pops up to replace the original one. Long-term, I agree the plants need replacing. So we have planted some Pittosporums underneath them, and as those reach maturity and fill in the hedge, we will selectively start removing Pittosporums. So it's a process and the endpoint will hopefully be the removal of the problematic Photinias. As usual, I appreciate your deep experience and opinions on these issues. I have a call into my arborist, and I guess we will use big gun fungicides. Will this be requiring repeated spraying to clear? In the short term, does it make any sense to spray water on the affected leaves?

That does look like powdery mildew. It’s also usually one of the easiest issues to get rid of. One of the best steps is to be diligent about clean orchard management every year. If you’re going the organic route, wettable sulfur can be used for powdery mildew. Many fungicides used for brown rot control are effective against powdery mildew as well. If the infestation isn’t too bad, you can clean off the fruit, and still eat it. I’ve cleaned my fruit with vinegar to get rid of the powdery mildew and then left it on the tree to ripen.Copper fungicide can also be sprayed on every part of your fruit tree, including the fruit. Nectarines, in my part of the country are one of the harder fruits to grow. Regular rotational fungicide management is a must for us. Below is a solid list of fungicides that work for the issue you have. Good luck! https://ipm.ucanr.edu/agriculture/nectarine/powdery-mildew/

duplicate post.. answers here: https://www.houzz.com/discussions/6376913/mini-rose-bush-powdery-mildew#n=4