I poked around the tree today looking for whiteflies, none around. And the castings didn't strike me as round, but I wasn't looking for that so I'll look again. You guys have me hoping it's this easy... I'm kind of suspecting glassy winged sharpshooter, as I came across a photo on the UC pest site, and realized that I've noticed (something very much like) them lately on an adjacent pomegranate. The sharpshooters also leave a white residue but I'm not sure it's a match to the heavy webby dust all over my tree. I'll look for their eggs and the scars the eggs leave on the leaves, tomorrow. If they are sharpshooters it seems like targeting them with wasps is recommended. Hmm that might make it time to call the arborist for a visit. Here is a link that might be useful: UC Davis Glassy-winged Sharpshooter

There have been numerous postings of success treating powdery mildew with milk. Mix up a spray of 3 tablespoons milk (any kind) to one cup of water and spray the plant throughly. I haven't tried this so would be interested in hearing if you have good results. Also, rather than repotting your fern do the following. Using a large serrated knife cut a deep circular core out of the center of the fern. Fill the remaining hole with fresh potting soil. This method works well on potted ferns including Rabbit's foot and Boston ferns. It may be necessary to do this twice a year.

One thing that should be understood about powdery mildew - once you see the symptoms present on the plant, it is typically too late to treat. Most fungicides available to the general public are preventatives, not curatives. At best, all you will achieve is to prevent the disease from spreading to new growth or unaffected foliage. The conditions on the already affected foliage will remain the same. In other words, you can't undo powdery mildew. On a deciduous shrub like a hydrangea that will drop its leaves soon, I wouldn't bother to treat at all. It's not worth the effort and it won't accomplish anything. Powdery mildew is primarily cosmetic in its damage - an otherwise healthy hardy shrub, tree or perennial will not succumb to something as innocuous as PM. Second, chemical fungicides are some of the most toxic of pesticides (I cringe when I read of someone using Orthonex or something similar). There are natural or low toxicity controls that are equally effective, provided they are applied early enough before the disease takes hold and is visible. These include the Cornell formula (baking soda and water), diluted milk and Neem oil. All season hort oil is also a reasonable choice. And none of these have the potential to damage the environment and the gardener as do the chemical fungicides. Finally, powdery mildew can often be controlled simply by correctly managing the cultural conditions under which the plant is growing. Watering late in the day should be avoided, provide good air circulation and sufficient sunlight and keep fallen leaves or other debris picked up. If grown in a container, never allow the container to dry out but keep the soil evenly moist but not excessively wet.

I was hoping to get some feedback from other people who have "David" to see how it performs for them. Rhizo, 10% infection would be pretty darned good if this were July or August, but here in PA May is not even powdery mildew season. Phlox normally does not get hit til near the end of summer, even the non-resistant varieties. My plant has severe enough infection to have total dieback on the bottom of the plant, and in the midsection of the plant the leaves are spotted. Only the very top is free, but we have 4 full months left to go. When I go online and read studies of powdery mildew, generally you don't see the studies make claims about resistance of plants or effectiveness of control products until late in the year; they are usually ALL fairly resistant/effective this early on in this climate. I spoke to the woman at the nursery and she was visibly surprised that I had that problem with that plant. She suggested trying to move it, but it doesn't have any place else it could go where it would be happy. When I pulled off the infected leaves at the bottom, it made the plant top-heavy which caused it to open up a bit as the stems all lean outward. That should help, but I am disappointed. My mother does not treat her phlox. She has some old unnamed garden phlox that is not meant to be resistant, her plants are huge and full and the earliest in the year they ever get a speck of mildew is mid-to-late summer. In a very bad year she might have dieback, but in many years they hardly get any and never once has she had it in the spring.