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A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Please forgive us, but Mr. Smarty Plants has been overwhelmed by a flood of mail and must take a break for awhile to catch up. We hope to be accepting new questions again soon. Thank you!

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Sunday - August 01, 2010

From: Las Vegas, NV
Region: Rocky Mountain
Topic: Diseases and Disorders, Watering
Title: Arizona ash tree with brown leaf tips in Las Vegas NV
Answered by: Barbara Medford

QUESTION:

We've had an Arizona Ash Tree in our yard for over 7 years it was doing fine until last summer, the tree seems to be struggling with the heat, its leaves look like they are burning up and turning brown at the very top, is there anything we can do to help it?

ANSWER:

According to this USDA Plant Profile Map, Fraxinus velutina (velvet ash) grows natively in your area of Clark County, USDA Plant Hardiness Zones 8b to 9b, so your problem should not be with soil or climate. Unless you are having a most unusually hot summer, hotter than last year, you need to ask yourself what in the environment has changed to cause that tree to have leaf tips browning?

We will do a little research into the Arizona Ash and see if we can find what might be causing a symptom you have not seen before. None of the sites we looked at mentioned any disease that caused that sort of leaf browning, but there were several mentions that this tree depended on an underground water source or was "riparian" meaning it likes river bottoms or other locales where there is a constant supply of water for its roots. We are wondering if perhaps you are having an unusually dry year in Nevada and that underground water has diminished. One source recommended deep irrigations of the tree two or three times a month during extremely dry spells. This would mean getting a hose down in the dirt around the roots, turning it on to a slow dribble and letting it run until water appears on the soil surface. The leaves browning at the top of the tree would seem to be indicative of this, as all the moisture and nutrition for the tree comes up from the roots. The leaves at the very top, the end of the line, as it were, would be most susceptible to moisture deprivation. 

Another possibility, although more remote, is that of ash borers. See this article from Colorado State University Extension on Ash Borers.  This article points out that borers are more apt to attack trees weakened from drought or other reasons. However, first see if there are any signs of the beetles before you try pesticide. For more information on the possibility of ash borers in your vicinity, contact the University of Nevada Cooperative Extension Office for Clark County. 

 

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