I am getting great growth right now on most of my trees. It really started to kick in about 6 weeks ago. Over the last few weeks the increased heat and sun exposure seems to be killing off a lot the growth for the trees getting the most sun exposure. Should I move these trees to a more shaded area? I'm a little disheartened by this.

I'm surprised that you have a heat issue at this time of year here,, if you have seedlings that are doing a heat stress now,, just wait another two months. I would speculate that there's some other issue besides heat/sun.

All seedlings we grow here use Anti-Stress 550 at a rate of 20 to 1 for the summers

Mark, if your containers are setting the the direct rays of the sun, you need to check the temperature of the tree's root zone. If you don't have a soil thermometer,get one. A soil thermometer is a essential tool for every container citrus grower. With black or dark colored containers, the sun can raise the root's temperature to 120+ in 1/2 hour's time. At such temperatures, the root are easily killed. A couple years ago I did a root zone heat test for containers setting in the sun. The temperature at one inch inside a black, or dark colored container's wall, reached 111F in just 5 minutes. One half of my containers are painted white, and the other half are black. During the winter, the black side is turned toward the sun to heat the medium, and during the spring and summer the white side is facing the sun to help cool the medium. You can also use objects like a aluminum foil wrap, or place your container inside a larger light colored container (pot in a pot). - Millet (1,021-)

Yes, the containers are exposed to direct sun on these trees. They are in Terra Cotta. Can you explain why the new growth dies first? I know new growth typically dies back during transplant shock, I just don't remember why.

New leaves transpire (loose water) at a MUCH faster rate than do the older mature leaves, therefore new leaves are the first to become dessicated. - Millet (1,021-)

Millet hit the nail on the head
Here in AZ things are a bit more extreme with temps and humidity, we regularly hit 115 at 4%
That kills roots in a heartbeat!
Terra pots will loose moister in our summers faster, container heat test here can reach 160 without a problem, in the nursery here I've wrapped rows of 15 gallon containers with bales of straw ,, that worked real well until the cost of straw wentt to high (so the straw ended up in the tub grinder... lol) I also used R rated exterior foam ,, the same foam they use to barrier homes for stucco,, I'm in the process of converting the entire growing fields to pot-n-pot systems, a huge undertaking in cost and labor.

All in all,, its a challenge,, but the results are worth the effort.

*If* I remember correctly??????, at soil temperatures above 96F, water absorption by citrus roots becomes greatly reduced, and at some point stops. Mark, if you only have a few trees, you can dig a hole to fit the size of the containers, and set your tree in the hole, which will easily keep the root zone cool, just watch for roots growing into the ground. When you water the tree, you will have to remove the tree from the hole to prevent flooding. Good luck. - Millet (1,021-)

I have 15 trees, but that is a good idea. Now the Rootmaker grounder makes more sense to me. I'm getting in over my head. Maybe I can buy some cheap fence or hedge type product to shield the pots.

Just an idea. You could cover the pots with alunmin foil to reflect the sun, or paint the pots white.

So at what soil temp will the roots start to die? 120F?

Same deal with heat here in Fresno, CA. I've recorded soil temps above 150 near the edge of black nursery containers. Of course, the south side of my house gets to 130 ambient temps on 100+ days.

The cache pot idea works VERY well, in winter AND summer from both extremes. However, if you don't have the cash or time and if it's temporary, use almost ANYTHING.

I've protected containers from sun just leaning white cardboard in front of them. As long as it's tall enough to cover the entire container plus soil area it helps tremendously. This protects them from radiant heat transfer.

The cache pot (pot in larger pot with large chunks of bark) insulates to also protect against ambient heat (conductive) as the bark can stay cool and wet from daily watering.