Dieback of Mature Fan Tex Ash

Q. I was cleaning up the leaves from my Fan-Tex Ash tree and noticed that there was sap leaking from 4 different limbs of the tree.  Attached are some pictures.  The tree is about 18 years old.  Although the first picture shows a small number of leaves remaining, the tree has always has had a nice canopy of leaves including this past year.   The tree is in rock much, but it receives nutrients (24-8-16) from an in-line liquid fertilization system.

Readers Fan Tex ash tree

I did some on-line research and the sap could be caused by stress (not enough water) or some type of borer.  The tree receives about 30 gallons of water each time it is watered.  In the winter it is watered once a week, spring and fall twice a week, and in the summer 3 times a week.  Is it common for this tree to have borers or is this problem likely caused by insufficient water?

A. The amount of water it is receiving sounds about right or possibly a little bit on the light side. It is definitely not being over watered. Your frequency of application also sounds about right seasonally. If this tree is surrounded by rock mulch then the amount of water applied may not be enough.

Look at New Growth

Look at how much new growth occurs every year. At eighteen years of age the tree is in youthful maturity. The tree should be growing at least 8 to 12 inches minimum every year of new growth. If new growth is less than 8 inches every year then there is a problem.

You are right in several things. It could be damage from borers. It could also be from stress such as a lack of water.

Ash Decline Disease

Fan Tex ash is an Arizona ash. Arizona ash has a problem with ash decline disease. For this reason, I no longer recommend planting any of the Arizona ash trees including Fan Tex. The tops of the trees could have developed ash decline even though this look is not typical of ash decline. 

Ash decline usually hits one or two branches at a time and causes dieback and slow growth and leaves scorching. It is also possible it has sooty canker disease. Borers are usually associated with sunburn of limbs lower in the canopy. If this tree were topped with a chainsaw it is possible that any of these three possibilities could be a problem.

Dieback of ash due to Ash Decline

A severe case of ash decline on Modesto ash

If this is ash decline disease, the tree is a goner and it will continue to slowly decline in coming years. I would recommend that it would be removed. If this is borers or sooty canker disease then some pruning might help it recover. If you decide to keep this tree, I would have a qualified arborist selectively remove the damaged parts of this tree. Certified arborists know how to prune trees and improve their ornamental value.

Fertilizer Injector

It is nice to know that these trees are getting part of what they need through an injection system that deliverables mineral fertilizers.

Rock Mulch

This is only a partial solution to successfully growing ornamental trees in desert soils. If these soils are covered in rock mulch then the soil is probably low in organic content. The organic content can be very important to ornamental trees growing in desert soils. Rock mulch causes desert soils to slowly become less and less organic over the years. Mineral fertilizers will not solve this problem. Either covering the soil with woodchip mulch that decomposes or continually adding compost to the soil will work. As this soil becomes more “mineralized” over time the tree may continually decline.

If the soil is covered in rock mulch, add compost to the top of the soil and water it in. You would do this once a year for the next three or four years but it is a slow soil improvement process. This is all hinged on whether you have rock mulch or not. The faster option is to make vertical holes with post hole diggers throughout the root area of the tree and backfill these vertical holes with compost. This gets the compost mixed into the soil much faster and produces faster results.

If this turns out to be borers than applications of systemic insecticides may be her only solution to the problem. In any case, someone needs to make a decision about what the problem is which determines the course of action.