I don't have indisputable results yet, let me be clear about that up front. But I am seeing some differences between my asters that underwent the milk solution/dormant oil experiment (full details in this link). Click on any photo for a closer look.
Here is the smooth blue aster (Symphyotrichum laevis) sprayed with the dormant oil solution. Unfortunately, it still has these brown spots that are spreading to newer leaves. However, this doesn't appear to be powdery mildew, so I guess that's a positive, but this plant is definitely struggling. It's also still a snack for the local rabbit, which is apparently enjoying the soapy vinaigrette.
Here is the aster sprayed with the milk solution. The white cast is dried milk, not mildew. So far the discolorations on the lowers leaves haven't spread to more foliage.
Since neither of these plants are dealing with an out-and-out mildew infection, it's impossible for me to say definitively whether milk or the dormant oil is the better fungicide. But the milk solution does seem to be keeping the plant healthier than the oil, at this point. I must admit, however, that the control aster is doing the best of all:
Results are even less clear with the monardas. Here's one:
And the other:
Can you tell a difference? I couldn't either! (For the record the first one had the milk and the second had the dormant oil.) Neither has powdery mildew or any other noticeable fungal infection, so that's great! I guess both solutions are working equally in that regard. But both of these monardas are being chewed relentlessly by insects, and neither solution is helping that problem. I suppose that's why "dormant oil" is meant to be applied when a plant is dormant!
Here's a look at one of the control monardas. As you can see, it looks just like the others.
I will probably apply another round of my solutions this week because we've had more cool rainy weather (what a shock!). I'll keep you posted on more developments, and I hope everyone has a great weekend!