Look at the link and tell me if that is it. You probably have citrus canker. There is no cure and it does not effect the tast of the fruit.

Here is a link that might be useful: citrus canker

Or citrus rust mite?

The Florida forum also guessed these two. I'm not sure how to tell the difference between rust and canker. The leaves seem to be untouched, so I am hopeful it is rust. The fruit themselves aren't losing color and the tree seems healthy otherwise. Is there any easy way to distinguish between these two infections?

They'll help you determine which it is.

Then let us know what you learn.

By the way, the rust mite is a tiny critter, too small to see with the naked eye.

But citrus canker is a nasty disease that all of us hope that's not what your tree has!

You can relax -- no sign of canker there. There may be a bit of rust mite damage, but the main problem you've got there is melanose, caused by Diaporthe citri. It's a fungus disease with large, heavy spores that don't easily blow in the wind, but which tend to rain down in droplets of water from higher in the tree, from dead tissue. Your photo shows a classic example -- fruit in near the trunk, where lots of dripping has occurred from above. In a home orchard, an easy way to prevent it is to remove all dead wood regularly. Copper-based fungicidal sprays in the late spring and early summer will also be preventive.

Malcolm M. Manners, Ph.D.
John and Ruth Tyndall Professor of Citrus Science
Florida Southern College
111 Lake Hollingsworth DR
Lakeland FL 33801

Hello Malcolm, its great to have someone with your credentials on here to help us newbie backyard citrus growers.

maybe you can help diagnose this problem and help me find a good treatment for my leaf miner thats almost completely taken over my Temple Orange, variegated lemon and working its way onto my grapefruits. ive already tried neem oil and a sesame oil based organic insecticide, neither of which made a noticeable difference.

leaf on my Flame Grapefruit
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Sanbokan Lemon
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Duncan Grapefruit
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Leaf miner damage to my Temple Orange
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The leaf photo is too out of focus really to tell, but if I had to guess, I'd say early greasy spot (Mycosphaerella citri). Also, the jagged edges seem to indicate some sort of insect feeding -- perhaps one of the several species of citrus weevil.

The first fruit photo -- don't know the exact cause, but it looks more like some sort of physical damage than a pathogen. But the later photos are almost certainly bird-pecking damage. As to why birds chose to do that -- who knows? Were there some nice juicy insects there at one time that they decided to eat?

i have a problem with leaf miner and Myllocerus undatus Marshall (little white weevil with gray spots)

Neem doesnt evrn seem to effect them, i spray it directly on them. what do you suggest, preferably organic?

Dr. Manners:

Thanks! So I guess I will cut any dead wood now, spray them with something for the rust, and keep an eye on them next April in case they need a pesticide. I'm afraid this will become a perennial problem in rainy years because these trees, which may have had full sun when first planted, are now in shade most of the day. They don't try off after a rainy evening. I'm going to turn off the sprinkler to this section of the yard, maybe that will help too?

barbers,
You said "...spray them with something for the rust..."

Please understand that the potential problem -- and notice that Malcolm said he saw little of that -- is rust mite rather than the fungus disease called rust. Very different things.