Persephone wrote:

The soil in this area is adobe (basic), but the people before me
mulched regularly, as have I, so I suspectthat over many decades of
modification the PH has become either acidic, or at least neutral. I
should have it tested some time just out of curiousity, though I don't
usually have problems like this.

Neutral won't work. It must be acidic. A pH of 5 to 6.5 is necessary.

I already have some Miracle-Gro; it probably won't kill the plant
to get a moderate application.

Miracle-Gro does more harm than good. It is a soluble nitrogen
fertilizer. Your plant is stressed and feeding it nitrogen is not a
wise move. The iron and sulfur are the right approach. Usually in
alkaline soil such as yours the only easy way to grow azaleas is in a
raised bed. Then the alkalinity of the surrounding soil doesn't affect
the azaleas. The raised bed only needs to be 8" to 12" high. Then use
a good acidic garden soil. If you want to raise acid loving plants like
azaleas, you will have to meet them half way by providing acidic soil.
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