Well, kathyga_z7, I was going to suggest things like a moisture problem (too much or too little), planted too deep, sunscald and some iron chlorosis but the leaves/shrub in the photo are too far away so I will give you some general comments with ways to identify these problems.

Make sure that the shrub has not sunk in the planting hole that you dug three years ago. If the root ball is planted too deep or has sunk too deep, the roots may have difficulty getting oxygen now. The plant should be approximately 1" above the surrounding soil. If planted even with the soil, well, that is still "ok"; I would only be concerned if planted deeper.

If the soil has too little water, the edges of the leaves begin to brown out inwards. Too much water can also cause root rot (roots are brown and spongy instead of white); symptoms of root rot resemble those of lack of soil moisture because the roots cannot absorb enough water.

Too much water or soil that drains poorly can change the pH in the area that is not draining well (even in the acidic heaven of Georgia), causing some iron chlorosis. Unfortunately, I could not tell if the leaf veins of the yellow leaves had dark green veins in the pictures; if they do then you have some iron chlorosis. If you wish, you can get a soil test kit to do a quick and dirty approximation of the soil's acidity near the bush. You can get them from places like Lowe's, HD and local nurseries. Then add some soil Sulphur or iron-chelated liquids products from your local nurseries once the soil drains well.

Try manually checking the soil moisture by hand for a week or so in order to get soil moisture under control and rule it out. Insert a finger into the soil to a depth of 4" and water the soil only when it feels almost dry or dry. Mark on a calendar when you water. Then set your drip irrigation or sprinkler to water about 1g on the same frequency. Ditto if watering manually. If your temperatures change by 10-15 degrees and stay there, re-check manually. If you get about an inch of rain or more, consider not watering if the soil feels moist at a depth of 4". Then maintain about 3" of any type of acidic mulch up to or past the drip line.

Then we are in the month of May.... In May-June some camellias shed their oldest leaves. Yellow leaves fall off randomly throughout the bush.

Camellias have very shallow roots so, as a safety precaution, limit garden work where roots may grow. Also, do not plant camellias near trees or shrubs with shallow roots... where the two start to fight for water. For that matter, do not plant shrubs of any type too close to each other in order to minimize fungal infections and maximize air flow around the plants!

Lastly, insects can also cause yellowing of the upper leaf surface (Camellia scale, Tea Scale, Peony Scale and Wax Scale). However, you checked this out and ruled out the possibility.

Does that help you, kathyga_z7?
Luis

Yes Luis that helps.
thanks so much for your in depth answer. I think it may be the chlorosis. I am also posting some close ups I just took of the leaves. It also appears upon closer inspection that I am getting dieback at the tips.

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Does this look like iron chlorosis to you? that would be my best guess. If you agree do I need to test the soil or can I safely just add something to fix this problem? I am trying to minimize my use of serious chemicals as I drain to a creek, so what can I safely add? Or is this one too far gone to save? If so what do I do to my soil first before I replace it?