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/

I sometimes try to throw the cornmeal under that plant but it all lands in one clump. Organic fertilizer hates being in a clump, so when you drop it down through the middle of the plant there is a Plinko effect which randomizes the droppage through the leaves. Cornmeal is one of the ingredients in many organic fertilizers. When the beneficial microbes in the soil decompose it, in about 3 weeks the end result is plant food. That is why organic fertilizer is said to be slow release. Actually it is slow decomp followed by very fast uptake by the plants.

Hi, lindalana The Veronicas are next to some Asters so I didn’t know if I was risking it spreading, but I usually don’t have a big problem with PM. Sometimes I’ve cut down phlox that have it, and other times I never get to them, and the snow knocks them down. Usually, they come back just fine. I planted with Biotone, which is about giving the roots nutrients, so hopefully, they come back healthy in spring. How fun to have a new puppy, but too bad it's allergic to dandelions. I like to let mine flower for any early pollinators that are out and about. I have soil/water with a high pH so also have a problem with calcium availability. I hope your soil test helps you figure it out for your gardens.

I have liquid copper for spraying but never got around to using it. What I use today is Orchard Spray which is sulfur for disease/fungus and pyrethrin for bugs. I mix one tablespoon per gallon and spray all my plants - usually less than 2 gallons in total. Pick off your worst infected leaves (if rhizomatous, you can use them for propagation as long as they have more healthy looking sections than infected parts). I spray in place because 1) I have too many (hundreds of plants) to remove to another area and 2) it is in the basement. Persistence is the key in getting mildew under control. Here are some of my begonias from the 16th of this month. I have sprayed 3 times this winter and see no more signs of mildew.