Please help. We live in Scottsdale Arizona and have three Orange trees in our backyard. Two smaller ones on either side of one older large one. They have all been doing well for the last few years, but the large one seemed to be showing signs of stress (not as much fruit etc.) In the last 2 months the leaves on the large one have begun to turn yellow and are dropping en mass. I will rake one day and the grass is covered with leaves the next day. It has very few fruit and did not produce many flowers this year. The other trees appear to be very healthy and are full of healthy looking fruit. We are very concerned, and don't want to loose the tree. Any help would be appreciated. :cry:

You will need to supply more information regarding the trees. Water, soil, temperature, and fertilizer information are most important. Pictures of the tree would help, include close-up of the leaves to help identify deficiencies, if you don't have pictures, describe the pattern of yellow on the leaves--when they drop does the petiole stay or drop with the leaf.

Skeet

It might be possible that the unseen roots might have been eaten by some underground pests or could be suffering from diseases or excessive fertilizers and the like. Most likely it would be root diseases or underground pests.

I'll just add that based on what we know so far it sounds like it
may be a severe scale insect problem. Let's find out. The leaves
that fell, where were they falling from in relation to the tree?
Were the leaves mostly falling from the interior of the tree first,
then the shaded areas in the canopy and then falling from the newer
growth near the outer portions of the tree? Does the top portion
of the tree look denuded as though it has been defoliated with a
black colored hue or cast to the leafless, exposed wood? Do you
see any young twig die back in the canopy and older wood die back
in the interior of the tree? The reason I asked those questions to
get us started was that there was a large tree in the UBC BG Citrus
forum from Arizona a while back that was covered with black scale
at one time. All we see left of the tree is mid to lower growth but
the top of the tree has almost been completely denuded with no
leaves showing with a pall, grayish black coloration to the wood.
A severe scale insect problem that has been on the tree for some
time will indeed cause a noticeable change in the number of
blossoms you will see and those blossoms that do set fruit will
have a higher degree of May and June drop than in previous years.
By the time the tree gets to Winter we may only be able to count
the number of fruit left on the tree in some cases. Also, the fruit
appear to be smaller in size than normal. We can go either way,
either we get a lot of small sized fruit or we get significantly less
fruit that also remains small in size. One thing for sure what your
tree is going through does not seem normal for this time of year.
We expect some leaf drop, mostly older leaves from interior and
shaded leaves to fall but they should have already done so if you
have had any cooling nighttime temperatures, more so after a frost
or two. Otherwise we may be looking at over watering, perhaps a
soil compaction problem, over fertilizing, even a gopher could
have caused this until we know more or better yet see some photos
of the tree and a photo or two of the trees that seem okay just to
serve as a reference point to establish what this tree looks like
compared to the trees that are not losing as many leaves as this
one is and has been losing. I am curious to see what the green
leaves look like on this tree and if there is any discoloration
areas that we can see on the fruit that are still on the tree.

Jim