Read Up on Ash Decline and Decide What to Do

 Does Ash Decline Exist? 

'Modesto' ash in a lawn and its dieback.

Read up on the tree disease here, here, and here and decide for yourself.

What is known?

In Las Vegas:

The "condition" was reported by landscaper Nanu Tomiyasu to Yours Truly in late 1980's on mature, 30 foot tall mature Modesto ash trees growing in a lawn near Cashman Field. The trees were given supplemental water and fertilizer but removed when they failed to respond. Yours truly took the State Pathologist, Dr. Wally Sheta, to the site where he thought it might be Ash Yellows and a sample was prepared and sent to the University of Florida for confirmation. The report came back negative for Ash Yellows and this "condition" was not pursued after the trees were removed. It has since been seen in Las Vegas on varieties of Modesto, Raywood, Fax-Tex and Rio Grande ash trees.

In Arizona:

This "condition" has been reported in Arizona by Jeff Shalau in 2018 after an investigation begun by Extension plant pathologist Dr. Mary Olsen started in 2009.

This condition has been reported in the Journal of Arboriculture by Bricker and Stutz in 2005 as a tree disease and MLOs are suspected to be the cause.

All trees infected by this condition die a slow death regardless of irrigation and fertilizer applied. 100% mortality. To my knowledge no pesticides were applied.

What is suspected?

The condition is a disease called Ash Decline in Arizona and caused by an MLO, a Mycoplasma like organism.

Because it is an MLO, it is thought to be spread by insects.

Infects ash trees with Arizona ash (Fraxinus velutina) genetics. Shamel ash (F. uhedi) is thought to be resistant. No trees other than those with F. velutina genetics has been infested.

What to do?

My recommendations are:

1. Remove ash trees showing symptoms after the dieback has been confirmed it is due to Ash Decline to prevent the spread of this condition.

2. Stop the planting of ash trees in the Las Vegas valley.

Bob Morris