Question
I peeled a perfect looking naval orange to find an area of about an inch that was completely black, next to the inside of the skin, about an inch from the navel portion.  We have never seen this inside an orange and are curious as to what this could be.  It looks like the orange itself, only black.  I took a picture with my cell phone if you would like to see it.  I looked through more than 30 pages of "citrus pests" and didn't see anything like this.  (I placed my home email address here as I am not sure if emails are filtered at work).

Answer
Hi Mary

Alternaria fruit rot primarily affects lemons and navel oranges, but it can occur in other citrus fruit. A fungus that only attacks citrus fruit causes this disease. Alternaria fruit rot often affects the inside of the fruit, making it inedible.

Alternaria fruit rot is best controlled in citrus fruit by providing plenty of water through irrigation. Avoiding drought stress is key to preventing alternaria fruit rot. Another way to avoid alternaria fruit rot is by providing your citrus trees with proper amounts of fertilizer. Black spot is best prevented by keeping infected citrus out of black spot free areas. Keeping your grove or garden free from infected plant debris is essential in controlling fungal diseases.

Being a fungal disease I would suggest Atomic Grow, which is organic, which raises the brix or sugar content in the tree.  It will  make your tree healthy so bugs go somewhere else, make fruit sweeter, bring in more pollinators for better fruit take and the best of all will save your tree.  kathy