This looks like it might be an over/under watering issue. The soil the plant is actuall growing in is beneath that layer of surface rocks. Remove the rocks (permanently) to look at the underlying soil. If it is soggy, you might want to review your watering.
BTW, you probably already know this, but, "Sweet plum" Sagretia Theezans is not a plum species. It is a subtropical plant. You can't treat it like temperate climate plum (prunus species) as freezing temperatures will kill it.
justin where are you as well, and is this plant grown outside, or inside??? Also, do you see ants on the plant? Often times these will get bugs... ants are usually a sign, cause they are feeding on the bugs. Often these type of plants will get scale, which will turn the leaves yellow at first, and will eventually kill the plant.
so, if it is not the watering, check for bugs, and be sure to look underneath the leaves...