The damage is to clusters of berries, clusters that form a kind of balled area of dark -- grey/black. It reminds me of honey-dew, but I'm thinking it isn't honey-dew because the darkened areas are confined to clusters of berries. It reminds me of a fungus because if I look close enough, there will be some white between a berry or more in the cluster.

This tree is the private residence of a beautiful singing Mocking Bird and his mate.

Just after noticing the damage (yesterday) I decided to prune all the damaged fruit and the Mrs. Mockingbird shouted me out of there.

Please help.

I have 4 mature weeping yaupons and just went to check for what you described.
Truly,fully berried in late fall, all I could spot were 4 individual berries left now in spring. The birds,especially robins, usually have eaten all berries over the winter. Fortunately nothing in the way of damage.
If you have a healthy yard and lots of native spiders, they tend to keep insects in control (except for bagworms).

You might want to google using the correct spelling..yaupon.