where do you live?

Is the tree in a pot or the ground?

In any event, I suspect a root problem. How wet/moist/dry is the stuff it's growing in?

MarkRPeterson,
Try this link.

Good grief. A nice list of diagnoses (horrors) for established trees. If OP's tree was obtained from a garden center, it should be from certified stock and, thus, arrive "clean."

OP's plant has been in the ground (?) for two weeks. The problem is cultural.

Hi Jean,
We live in Southern California--Ventura County. The trees are in the ground and the soil is clay. Watering is every other day for 15 minutes--lawn sprinklers. Any ideas or advice?

Thanks!!!

This early after planting, it's important to keep the rootball evenly moist. Doing so often requires that the water be applied directly to that area. Every other day for 15 minutes may be accomplishing that, or it may be keeping the soil too wet. The only way to know for certain is to stick a finger, or a trowel, in the soil, then look/feel.

Avocados require excellent drainage. Because of that, the frequent recommendation is to mound up the soil in the planting area to at least 8 inches, then plant the tree in the center of the mound. In that way, one can avoid excess water at the crown of the tree. Soggy soil is the all too frequent reason for root rot in avocados.

Unfortunately, no treatment is available to stop root rot once it begins.

I suggest you contact your county's Extension Service office. More than likely they can offer specific suggestions for an avocado in a home garden.

Locate contact info for the Ventura County's office using this map:
http://www.csrees.usda.gov/Extension/

Jean,
who gardened for 30-some years in Long Beach, CA

Here is a link that might be useful: locate your county's Extension Service office