Normally its a root area/soil problem. Too much water or soggy soil. Possibly too cold. possibly a root diseases. pictures would probably help.

Maybe not enough water. What are your watering practices? What is the planting medium? Where are the trees (outside, inside)? (I have mine outside, water every day in this heat and they are still dry every day!). Your posting does not give us enough info to solve your problem.

Yes, we need more detail...

You could even have bugs...Please tell us how the roots look, the mix, and any cultural habits you have to share.
Is it outside?

Mike

Things I'm doing or might be doing wrong(correct me if I'm wrong):

_I haven't transplanted in over a year
_Still in a 6 inch pot
_It's in a Northern facing window indoors
_Window is open even on days when temperatures fall down to the lower 50s
_Haven't fertilized since the late winter of this year
_I haven't misted this plant in forever
_Humidity is low

Things I believe I'm doing right(correct me if I'm wrong):

_I let the soil dry between waterings
_It's getting sunlight(though possibly not enough)
_The heat mimics a tropical climate indoors during the summer where it's hotter during the summer months, cooler during the winter months never falling below 66

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Yes, I am disgusted by the neglect these plants are receiving from me. But please keep in mind, most of the neglect is a result of the scale outbreak I've been dealing with. So, for example, I haven't transplanted any of my plants recently because I had to throw out my soil, I had to throw out a LOT of pots, I had to trash some of my plants that had scale because not a single treatment did anything to the problem, if anything made it worse. So, the treatment resulted in loads of neglect, and what upsets me even worse is some of the forms of neglect is going to remain unchanged as I try and recover. Yes, I'm FINALLY recovering because I haven't seen scale recently.

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As for the photos, I will post them tomorrow at some point.

Scale, and other pests and diseases, more often than not attack trees that are under nutrient or water stress.

Here are the photos.

This is a full shot of my Tangerine:
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From a distance, it looks healthy, doesn't it?

This is the first leaf that fell off while snapping photos:
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This is the Second newly fallen leaf:
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This is one of 2 new areas of growth:
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Despite the premature defoliation, my tangerine tree still has 2 areas of new growth. But based on what happened to my lemon, I know this doesn't mean anything.

This is the other new area of growth:
{{gwi:615451}}

Sorry for the pictures being so crappy. I still don't have a better camera, and I wish I did. I hope the pictures are at least clear enough to be of good help.