Here are some pictures of the mold and the browning edges.

If it is on the back of the leaf it may be indumentum. That is a highly desired characteristic that helps prevent insect damage. It is a brown fuzz but should only be on the back. It is normal on some varieties, especially ones that are Yak hybrids. Other possibilities are: * Sooty mold growth on stems and petioles is a symptom of Azalea Bark Scale, Eriococcus azalea, and Cottony Azalea Scale, Pulvinaria floccifera. These small sucking insects feed on the bark and exude a sticky substance that turns the stems black. A scale infestation is indicated by sooty mold on leaves, yellowing of leaves, and twig dieback. This scale is most obvious from May through June when white egg sacs may be found in twig forks. Heavy infestations over several seasons may kill plants. Overwintering immature scales (nymphs) are about 2 mm long, gray, and are usually found in twig forks. This scale primarily attacks azalea and rhododendron, but has also been found on andromeda, maple, arborvitae, willow, poplar, and hackberry. Azaleas can tolerate low populations of this scale without injury, and if there are no yellowing leaves, no treatment is necessary. Beneficial predators and parasites will usually provide adequate control of light scale infestations. Examine egg sacs for holes which indicates control by parasites, and look for predators such as ladybird beetles. To control heavy infestations, spray dormant plants with a late oil spray to kill developing nymphs on twigs. If necessary a 2% summer rate of horticultural oil may be applied in July after all of the eggs have hatched. * If a leaf has brown areas with white spots, it probably has a local fungal infection of Pestalotia rhododendri. This is seldom controlled with fungicides and is best mitigated by good sanitation and avoiding excessive moisture. * Grayish areas on a leaf may be caused by frost damage. If the plant variety is too tender or the plant has not hardened off and is hit by an early frost, this may occur. Application of fertilizer after mid-June my stimulate tender growth that is frost susceptible. * Wind and cold damage is indicated when the edges of the leaves become distorted and turn brown. This occurs frequently in plants that may be in a colder climate than recommended or in a location with severe exposure. Provide protection from winter winds and winter sun. Note, boron poisoning or fertilizer burn will create the same symptoms except uniformly over the plant rather than just on areas exposed to the sun and wind. * Powdery Mildew (Microsphaera azaleae) usually result in a grayish white, powdery coating or fuzzy white growth on upper or lower surfaces. This is more prevalent on deciduous azaleas and sometimes it affects the lower surface more. Entire leaves can be covered. In late summer and fall, small black specks may be found in the white areas. Powdery mildew is more severe on shaded plants. It is favored by the high humidity found in crowded plantings and damp locations. The disease is more severe during periods of cool, moist weather. These fungi produce spores on the surface of the infected leaves which are spread by wind currents to surrounding leaf tissue. These fungi overwinter in the bud scales for initiation of infection next season. Here is a link that might be useful: Rhododendron and Azalea Troubleshooting

Cathy, thanks for sharing what happened with your milkweed. I wrote the above before your reply was posted. Which milkweeds are native to your region? Swamp? I can't scroll up to see if you mentioned Common since I'm on the preview page. I grow what's native here, A. fascicularis, but possibly climate change has moved faster then the native milkweeds have adapted? Has your climate changed? My milkweed was so bad looking almost all spring and early summer. It had red and black splotches along with white powdery mildew, some white flies, even the Asian citrus psyllid (invasive species) came over to sample it-maybe it liked the whitefly debris. I killed most milkweed bugs and aphids manually. The black mold/mildew then came along--summer through November. Also insect damage and curled leaves. There were a few small, odd looking blisters on a green leaf, rarely though. What a battle. Thanks for sharing what you went through, that was really a lot of work and dedication! Maybe if left, the native MW's would adapt? I wonder, but don't know.Taking out 100 plants! what a job! And all those other types you tried :o( I know that as a kid, summers here were dry and hot, and now summers seem shorter and not hot like they used to be. Used to be that July 4th's were HOT evenings, but for the last 10-15 years, I usually wear a sweater watching fireworks, the young kids wanted a blanket 2 years ago! Very strange. I used to wish it would be in the mid 70's all year, but now I wish for the "old days". I wonder if getting ahold of some A.fascicularis seeds from a milder zone within it's large native area (most of Ca.) would make any difference. That would be good to know if the native milkweed varies genetically within it's native range. Maybe invasive insect species have weakened it and it hasn't adapted. Sorry you had to go through all that trouble!

I agree with everything tony c m said. I would clip off the affected leaves and pick off what I can on the insect with my fingers on the rest of the tree and spray everything I can on that tree. You did not mention if your tree is in a pot or in ground. If it is in the pot then spray the pot too and keep it away from other plants. Repeat this a couple more times within a week or ten days and you should see good results. I use Safer Brand Garden safe insect soap. It is non toxic and made of seaweed extract. Get the concentrate so it will be cheaper in the long run. The bottle is like Aqua color and the cap is Purple. Had this problem a few times with new trees but seems to not return after the first Winter here in Michigan. Good luck