I am new to growing citrus and I think I've got a sickly plant. I live in San Francisco, and my trees are in a nice, sunny spot in front of my bay window.

I have a Meiwa kumquat that I got from Home Depot, it is about 2 feet tall. I've had it for about 3 months and it seemed to be doing fine, and all of a sudden about two weeks ago, it started dropping lots of leaves daily. It is in the same soil with the same fertilizer as it has been since I first got it and replanted it (just a mix of potting soil and MiracleGro citrus soil, and some MiracleGro citrus fertilizer...I know, nothing fancy, but my Meyer lemons seem to like it ok). The kumquat also put out lots of flower buds recently, but they only last for about a day before wilting.

A few days ago I noticed that the leaves at the end of the branches (new growth) have brownish patches on them, these leaves drop a few days after the patches appear. I also noticed some tiny white spots on the leaves and on the branches -- I can blow them away so at first I thought it was just dust...but they are only on new growth, and yesterday I noticed the same white spots on my Meyer lemon tree, which is an adjacent pot. Is this a fungal infection? How should I treat it?

Any help is greatly appreciated!