SuperThrive's expensive and there's no clear consensus on whether or not it even does anything. I'd rather try something else. Trunks still green under the bark but it looks like it might be loosing some of the newer branches.

Ok..I am going to make a bold statement, not on what I believe, but what I have seen.. Count the too much sun or not enough out.....I have property in the Carribeans, where I have citrus growing under trees that are greener than the ones in the sun all day. The leaves are always yellowy on the ones in the all day hot sun, but produce lots of fruit and flowers. The ones under the trees, produce lot of green leaves, and less fruit and blossom. 1. I would first check the soil and make sure your roots are evenly moist, not wet or dry. If the soil is cruddy, then amend it for the roots sake. It has to be well draining and not compact, or it will affect root function causing all these problems. While your at it, take a gander at the roots. They should be whitish.. 2. I would then check the next most important thing you can do to keep a healthy tree, your PH. If your PH is not on the acid side, no matter how much you fertilze your tree, it will not take up nutrients properly. 3. Next, check for bugs. If it is being attacked, the leaves will fail, turn yellow and drop. Almost always though, the most common casue of problems for citrus is unhappy roots or the wrong PH. Usually the "soil" which causes your roots to fail and not to their job.... As for the sun, too much or to little, I have many that are perfectly healthy here and on the islands that are very healthy in either or. My problems along with my friends in Florida have always been root related due to poor watering habits, or poor soil, or root rot. Attack these three first, then make your next move. Forget the fertilzer for now. Please, make sure your roots look good and are doing their job first, before applying fertilzer. They could become toxic instead of beneficial such as happened to mine in the past. Roots should look white and soil should be well draining..:-) Once you have done this and all is ok, we can come here and suggest some great fertilizing methods for ya..ok It's not to late. Hope this helps you rid one problem at a time. Mike..:-)

With just this limited photo, definitely spider mites. That speckling on the leaf is a classic sign of spider mites along with the webbing. I would continue treating as you are planning on doing. And yes, definitely you should be fertilizing, you can search and see how container growers fetilize (usually with Dyna Gro Foliage Pro with every watering), and make sure that your soil is not too dense. You may need to re-pot using more porous potting mix, but cannot tell as we don't have a full photo of your tree and a photo of your soil to tell you for sure. And of course as much light as possible. Preferably a south window. Patty S.

According to the "book" and what I've read thornless don't yield as much. Whether it's enough to matter to the average homeowner I don't know. Also IME Persian Limes (especially) & Key Limes are very underrated for their cold hardiness. TRUE Lemons are over rated. I have about 20 citrus trees in the ground and my Tahitian lime is one of the hardiest & most cold hardy here in zone 9B. The only citrus trees I have ever lost to low temps were a full sized Harvey Lemon and a mid sized Varney Navel tree back in our record 2010 freeze here when he got down to about 20. Nothing else even got burned. I have seen a lot of nurseries saying Tahitian limes are cold sensitive and I have not found that to be the case. Lemons I have.