Could you post a picture of the actual wounds from which sap oozes? Is citrus gummosis common in AZ? I am not suggesting that it is gummosis but it is something to investigate.

The pictures look like some sort of residue from a borer. My garden was infested with borers last summer and that is how the plants looked. I think gummosis is amber colored and lays flat on the limb. I bet if you removed the gummy stuff, you will find a perfect hole underneath.

Thanks for the comments! I'm quite new to growing citrus and know many of the flowers don't turn into fruit and even the fruit that begins to grow in Feb/March will fall off by May, however I cannot recall the fruit turning black before falling off. The color is what is concerning me a bit.

I did knock away the amber colored sap in two places. One showed a vertical scar and the other is in the picture below with an open wound.

I will look into gummosis and hopefully find ways to treat it. Thanks!

I am nearly certain you don't have gummosis; as for the young fruit, it normally falls when it is yellow; but if you leave it, it will turn black. All ahead full steam. If you have problems with borers, I would recommend ISD (Imidacloprid Soil Drench). The Imidacloprid enters the plant as a systemic, killing anything that bites or sucks on the leaves/stems; but not killing the beneficials.

I had this same issue appear in a Page Mandarin tree over the last several years. The tree was productive, but it kept getting worse and I finally gave up on the tree. The holes were not round, but more rather looked like narrow slits. I live in Las Vegas so I wonder if it is something in our area? I never saw it on any other of my trees.

I cannot dismiss early stage gummosis by looking at the picture above. I think a local expert should look at the tree. If this appeared on my roses I would say it is the work of a sawfly but on citrus? In the meantime I would isolate the tree if potted, treat the wounds and the soil with copper and if more of it appeared I would cut off the affected canes making sure the wood exposed looks nice and healthy. To investigate further ones needs to look at the state of the foot below the soil so a little digging may be in order. The fungal disease called 'Citrus gummosis' starts at the root and foot but there are also other types of gummosis.

Also take a look at this, paying attention to 'citrus gummosis' and 'Rio Grande gummosis'

https://cals.arizona.edu/extension/ornamentalhort/plantprotect/citrusdisease.pdf

Same story as our Vegas friend. I have a 5 year old Page mandarin in the ground that is doing the exact same thing. It is the only citrus out of 20 other citrus varieties in the ground that has this problem. I'm in Phoenix, AZ and this problem only happens in the hot Summer for me. It may not be a disease. I'm guessing Page bark is less sun/heat tolerant.