First of all I would check the Ph of your soil. If the Ph is incorrect it can lock up the nutrients. This will prevent the tree from using them. Citrus like a Ph of 5.5 to 7.0
Andi

Patty, if veins are pronounced dark green and inside is yellow, if it were my tree I'd treat w/iron.
To be honest I don't care for the spikes..I prefer either liquid or granuals, something that's going to fertilize the entire rootball..when you use spikes/stick it usually works on the one area.
I have read this in several plant books. (not only for citrus but other types of plants.)
Did you stake the plant in one spot or break up in different locations? Toni

Hi Patty,

This link might help. It shows the various effects of all types of mineral deficiencies...

http://www.flyingdragoncitrusnursery.com/deficiency/index.htm

Here is a link that might be useful: Deficiency Images and Explanations

citrusboy:
Thanks for uploading the link. I save it for future ref. That is very helpful and good to the point.

Thanks!

According to the link, it's definitely iron.

I'll check the pH.

If the pH is high, can I apply sulfur and maybe work it into the top few inches of soil? Or is there a better treatment?

Elemental Sulfur can harm the tree is used improperly and is slow acting. You can use an acid such as sulfuric to accomplish the same in a shorter amount of time but the same risks apply. I would only use a small amount of acid added to the irrigation water.

When you check your soil pH you should also check the pH of the irrigation water. The more accurate testers and rather expensive but you can have a lab test your samples a lot cheaper. They would have better equipment and accurate results. Its also possible to use a topical application of iron sprayed on the canopy of the tree. The latter is a quick bandaid approach and will not give lasting results.
Andi

If your soil pH is too high, you could try iron sulfate--two birds with one stone...

HTH.