Do your trees have Pinks Disease? It’s particularly prevalent in high humidity areas.
Annette McFarlane: Take a close look at this image. Initially you may mistake it for lichen (there are some small lichen surrounding it). In fact, it is pinks disease (Erythricium salmonicolor). It attacks a number of different native and exotic trees in areas of high rainfall. Stems are eventually ringbarked and die. Prune all infected limbs; increase air circulation; spray with copper; followup with a good nutritional program including foliage applications of seaweed and liquid silica and potash. Tangelo trees appear particularly susceptible.