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Wednesday, October 11, 2017

Limbs Dying in 20 Year Old Arizona Ash

Q. My Arizona Ash tree is about 20 years old. Six or eight of it's limbs have dried up and died, within the last couple of weeks. Can you tell me the cause of this and what I can do to prevent more from drying up?

Ash tree showing gradual branch dieback from ash decline
A. Judging from your description, most likely your tree has a disease called ash decline. It is important to know the scientific or Latin name of this tree, Fraxinus velutina, because it is called by many, names in the nursery trades including velvet ash, smooth ash and desert ash among others.
Ash tree showing the first stage of yellowing due to ash decline
            For this reason I just tell people to not plant ash trees in general in the larger metropolitan areas associated with the Mojave, Sonoran and Chihuahuan deserts of the southwestern United States. There are plenty of nurseries still pushing these trees and they are aware of the problem. Caveat emptor, buyer beware.
Close-up of leaves yellowing and scorching due to ash decline.
            About 4 or 5 years ago I stopped recommending the planting of any type of Arizona ash or Modesto ash in the Las Vegas Valley. Arizona ash also includes Raywood and Fan Tex ash which are a type or cultivar of Arizona ash. We don't have a history yet of these trees, but I would be leery of ash trees labeled as Bonita and Fan West because they have Arizona ash genetics in them.
Advanced stage of ash decline where entire tree dies. This can take up to 10 years. Is ash decline capable of spreading from tree to tree? The answer is probably yes. This is the reason I am telling people to remove these trees after ash decline has been confirmed.
            In the mid-1980s in the Las Vegas Valley in North Las Vegas on Modesto ash and we tried everything we could to cure, rectify and remedy this problem with no success whatsoever. The trees ultimately died. We involved the state plant pathologist who sent tissue samples to Florida thinking it was a disease called ash yellows and it came back negative.
            Personally, if these trees are getting adequate water, not too often and not too little, assume it is ash decline and remove them as soon as possible. We don't know much about the disease, we don't know how it is spread so we should get rid of them and not plant them again until we can figure out what this problem is and how to stop it.
            Look for suitable replacement trees. If these replanted in a rock/desert landscape then replace it with a desert landscape tree that will give you the same benefits. To our knowledge this disease is not present in the soil and is restricted to certain types of ash trees so replacement trees should be fine if they are not ash.

1 comment:

  1. My entire neighborhood is affected by this with a majority of the yards having ash planted in them by the developer in the mid 90's. Here we are, 20 years later with 30' tree's that are going to need to be taken down eventually...what a shame. Thankfully mine was affected while small and a volunteer sumac was coming up beside it so after a year I cut down the 8' diameter ash and had an automatic replacement. Neighbors no so lucky.