Ash Dieback or Ash Decline? They Both Kill the Tree.

Q. I have a 23-year-old ash on a drip system with 10, five gallon per hour emitters watered twice per week for 30 minutes. It is located on a southern exposure and planted in a rock mulch.  It has a drip system.  The tree has begun to lose leaves and limbs are dying. Is the tree just old or am I doing something wrong?

Ash tree showing die back. This is not the tree mentioned here.

A. You are watering this tree about 50 gallons a week if all the emitters are working properly. As hot weather is upon us, I don’t believe that this will be enough water to support this tree.

That is probably enough emitters for that tree if they are spaced 2 to 3 feet apart under the canopy of the tree. If the emitters are grouped too closely together much of that water will be wasted. You want to wet about half the area under the canopy of the tree each time you water to a depth of 18 to 24 inches.

Instead of just placing emitters under the canopy of the tree, an alternative method is to place other plants under the canopy that require water as well. I believe there are several advantages to the tree in doing this.

Ash decline

May 1^st is usually the critical time when we increase the frequency of applied water from once a week (beginning the first week of February) to twice a week.

Unfortunately a couple of the ash tree varieties have been developing this kind of problem since before I arrived in the Valley in 1984. I remember during the mid-1980s I was called out to look at some very large Modesto ash trees near downtown North Las Vegas. These ash trees were on city property and surrounded by turfgrass or lawns that were in very good condition. The trees had leaves which were curling up and dying as well as branch dieback.

Ash decline will kill the branches of ash trees. If the trees are not pruned and maintained properly these trees will become a safety hazard. This ash tree limb from an ash tree with ash decline broke from the tree and hit this house during a mild wind storm.

The plant pathologist for the state of Nevada and I sent samples to pathology labs looking for some answers. It first came back as a disease called ash yellows but it was later found that this diagnosis was incorrect by the same laboratory. The landscape contractor I was working with, Nanu Tomiyasu, had tried fertilizers, increasing the amount of water to the tree even though it was in a lawn and nothing seemed to help. He was desperate for answers.

Dieback occurring on fantex ash

Fast forward now to 2015. This disease on ash, first found on Modesto ash, has been found on other ash varieties like Arizona ash that have been introduced into the Valley since that time. Plant pathologist from the University of Arizona has acknowledged this disease and written about it http://ag.arizona.edu/pubs/diseases/az1124/ calling it Arizona Ash Decline and the University of California has termed it Ash Dieback.

There are some assumptions about this disease but everyone seems to agree that it is not controllable and eventually the tree will become a hazard and should be removed as the disease progresses and limbs die more and more. Increasing the fertilizer and water the plant receives will not help.

I have no evidence for this but I assume that this disease is transmitted by insects such as the Apache cicada which is common here or whiteflies. Putting ash trees in less stressful environments such as lawns or supplying enough water to the tree roots, seems to help prolong its health. I am telling people that this tree will be short-lived in our environment, 10 to 20 years, until this problem is resolved.

They should not be confused with dieback of limbs when older, established ash trees are no longer in lawns but part of a landscape retrofit to desert landscaping. In my opinion, this will shorten the trees life. Before the tree becomes a hazard, please remove it. If this is ash decline there is nothing you can do to save it.