This afternoon an Agricultural Inspector from the California Department of Food and Agriculture inspected all of our citrus trees. She was combing the neighborhood looking for the Asian Citrus Psyllid, which is new to our area and can carry Huanglongbing (HLB) Disease or "citrus greening". I did not realize that HLB is now found in Orange County and Mexico, so both north and south of us. She was looking for the psyllid, which is a tiny critter about the size of an aphid, and for signs of HLB, including mottled leaves. One of our trees, the newer Gold Nugget Mandarin, caught her attention. It does have mottled leaves this spring. I'd figured this was cholorsis, partially from our wet winter. She sampled 20 leaves off the tree to bring back for testing. They only notify people if the results are concerning for HLB. So we shall see. Here is a link to their website for more information and recommendations.
