Citrus rust mites (yellow wedge shaped arhtropods) can cause visual damage to the rind of the fruit by turning it dark brown to black. The internal quality is still fine to eat so this should not affect home orchards.

Citrus rust mites can cause symptoms such as browning or darkening of round oranges. These pests are very small, deep yellow and wedge shaped. You will need a 20X hand lens to see them, as they are not visible to the naked eye.

A generation may be completed in one to 32 weeks. Rust mites feed on the outside exposed surface of fruit 1/2 inch or larger. The feeding destroys rind cells and causes browning on mature oranges and blackening on green fruit.

Most damage occurs in early spring to early summer, although damage is possible throughout the year in groves not treated for other pests. The mites have no specific predators, but other mite predators will feed on them. In early spring, check leaves for mites and check fruit after it reaches 1/2 inch in size.

Residents can use ultra-fine oil as per label directions now through mid-August as per label directions to help control these pest populations. Do not apply later than this time as you can hinder fruit maturity. Refer to the Home Citrus Production Guide for a complete spray schedule.

Home Citrus Production Guide link:

http://www.lsuagcenter.com/en/lawn_garden/home_gardening/fruits_nuts/
Louisiana+Home+Citrus+Production.htm

Citrus website:

http://www.lsuagcenter.com/en/crops_livestock/crops/citrus/