I just noiticed the same thing with one of my tipu's today. I have it planted in my grass and I am wondering if it is not getting enough water? If you find out anything please let me know.

Interesting. Your tipu is in a lawn area, so I am assuming that it is getting a shallow watering several times a week as you water your lawn. Are you also giving it a deep watering every so often to promote deep roots?
How long has your tipu tree been planted? What do you think is happening? I have deep watered my Tipu tree (which is in a desert area)since my first post. It dropped more leaves, and then a couple days later looked a little better but not good.
As you can see there has not been any help from others yet regarding our questions yet. I was hoping that a regular on this site "AZTRELVR" would respond. That person always seems to have great info and fixes. Let me know if you have heard and/or done anything to help the Tipu problem. Good luck.

I did exactly what you mentioned and deep watered it and I have a little new growth but nothing earth shattering.

Yellowing leaves (chlorosis) could be an indication of overwatering, underwatering, nutrient deficiencies and normal leaf shedding. Yellowing on new leaves indicates a iron deficienty. If your yellow leaves are older it indicates an nitrogen deficiency. With this commonly you will see green veins with yellow tissue in-between.

Before you grab the fertilizer bag know that soggy or cold soils can prevent the absorbtion of nitrogen, and especially iron, from the soil. So first make sure you are watering correctly (deeply) and not too often. Tipu trees are in the legume family and they are able to 'make' their own nitrogen. Great news - you don't need to add nitrogen fertilizer to these trees (or mesquites, palo verdes, acacias, etc.) If you determine you have an iron deficiency, use 'chelated' or water soluble iron fertilizer.

How big are your emitters? If they are one gallon per hour, your tree is getting 8 gallons every two weeks. This may not be enough for a tree of that size. If it were mine, I would change the emitters to 4gph and leave it on the same schedule. It's always better to really soak the root zone and then let it dry a bit before watering again.

If your new growth looks good, I wouldn't be too concerned. Many trees shed their older leaves just before, or as, new growth appears. I've included a link to the U of A's publication on nutrient deficiencies which has great pictures and recommendations.

Let me know what happens.

Here is a link that might be useful: Iron Deficiency