Dick E. wrote:

I'm in San Diego County, inland.
On a hillside of clay I have a lovely, fairly elderly, pyrocantha. It
has lovely white blooms on it right now..
And - on some of the outlying bushes there is a white 'fluffy' sticky
white mold or mildew. Tiny fibres result and grow from a white sort of
haze which covers certain leaves and stems. It definitely changes the
color and health of the plant, and I left alone it will kill the
branch.

If there's any way I can avoid spraying a toxic substance (to the birds
who feed 10 feet away), Please advise. My dear, ambitious wife wants
me to take a pail of water and ammonia and wash the affected parts of
the plant, maybe with a brush! Shall I?

Lack of air circulation? Tried thinning the crown?