Lorraine, I'm in the same boat. I live in San Diego and have a dwarf Santa Rosa plum tree that I've had at least 4 years. This is the first year that I've had a significant amount of blossoms set fruit (although last year I moved the tree from a pot to in the ground a bit late in the year, losing almost all of my blossoms). Some of the lower ones are yellowing and will probably fall off. I've got my fingers crossed for this year.

Thanks akaMaineGrower for the comment and suggestions. I'm going out in a little bit to check on the life of the branches, but I wanted to run a comment past you that the rep from my County Extension service told me. Like you, I would believe that lack of light would cause issues like this, but apparently, getting sun can be the issue. She sent me part of an article by someone named Walter Reeves which stated that lichen usually colonizes on plants who are already sick in some way. From this ailment, they tend to thin out, thus allowing sun on branches that then encourage the lichen, primarily the algae portion of what I call the "ugly sandwich". Once the algae takes hold, the fungus isn't usually far behind. But again, these plants are more than a decade old, not in high moisture areas, and most are super full. They don't have "holes" in growth that would explain Mr. Reeves' comment. Ok, now I'm off to go check on the branches to see what life they have left in them! Watch, knowing my luck with this Psycho Lichen, they'll be healthy branches! :) Thanks again! Elizabeth

Dwarf isn't a factor in pollination success. If variety and bloom timing are right a dwarf will pollinate a full size tree as well as anything else.

the one with oragne flowers appears to be a variety of - perhaps - misletoe; but the flowers in CA are white. This is probably a form of parasitic plant common to your area.