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Tuesday, September 9, 2014

Why Does My Ash Tree Have Dying Limbs?

Q. I have two, twenty-year-old ash trees that appear to be dying. I have attached pictures. The smaller tree is a Modesto Ash and it started losing limbs about a year ago. The bark is now separating and it looks like an old stump with a few sprouts. The other is a Rayburn Ash. It just began having limbs die this summer but is accelerating. I am also noticing ash trees all over our neighborhood in the same condition. What is happening and what can I do to save these beauties?

A. I'm sorry to hear about your ash trees. This is a fairly common problem with ash trees in our desert Southwest. I have been dealing with this problem, mostly on Modesto Ash, for about 30 years. I no longer encourage people to plant ash trees in our climate.
Plant samples have been sent to several plant pathology laboratories over the years and no one has been able to find a disease problem.
We have been calling it ash tree decline but we do not know why it is happening. Fertilizer applications and increasing the water does not seem to help.
Modesto ash with limb dieback
The trees seem to dieback from a lack of water to some of the limbs but no one is certain why. At this point all I can tell you is to remove them when they get to the point when they become a problem to public safety or they just look bad.
The one in the side yard could have suffered from a lack of water from the picture. Modesto Ash in particular would benefit from wood mulch applied to the surface and given liberal amounts of water.
Check for borers underneath the bark that pulls away from the trunk. I suspect the trees may have been stressed either from the decline or water. This is a prime target for boring insects trying to finish off the tree.Once trees are heavily stressed there is not much you can do to prevent a borer attack to the tree. They will infest the tree and finish it off.

1 comment:

  1. Dear Bob,

    I am an Extension Agent in Yavapai County, AZ and have been following this disease for several years. I recently met with Dr. Jean Stutz and she and I discussed this disease. Her feelings were to avoid planting the Modesto and other susceptible ash trees. In my experience, poor soils, poor planting, inadequate irrigation, and physical wounding from sunscald and improper staking are usually observed on failing trees. In a couple of instances, trees have recovered following improved irrigation and mulching. You are probably aware of the papers by Bricker and Stutz (Journal of Arboriculture 30(3): May 2004, pgs 193-199 and Journal of Arboriculture 31(5): September 2005, pgs 257-262). This phytoplasma is elusive (the papers describe sampling trees with symptoms without finding the pathogen). Thanks for getting the word out about this "syndrome".

    Regards, Jeff Schalau, Agent ANR, University of Arizona Cooperative Extension, Yavapai County, jschalau@ag.arizona.edu