   Ash Decline in Yavapai County - June 27, 2012 Jeff Schalau, Agent, Agriculture & Natural Resources University of Arizona Cooperative Extension, Yavapai County In the summer of 2009, I was called by municipal landscape professionals to look at some ash trees with unusual symptoms in Prescott Valley. That same summer, ash trees in Chino Valley displayed similar symptoms. On the sites with symptomatic trees, multiple trees were affected, but some of the adjacent ash trees were growing normally and had no symptoms. This summer, I have received several phone calls and digital photos of ash trees in the Verde Valley displaying similar symptoms. The aforementioned symptoms include: ash trees with dead and dying branches; affected trees had some new foliage trying to emerge from buds lower on the branches, but this new foliage was greatly reduced in size and never attained the size of normal ash tree foliage (these tufts of foliage are called “witches brooms”); the two or three year’s previous growth rates on affected trees were greatly reduced as indicated by bud scars (2-4 inches of new growth rather than a foot or more); and in one case, an ash had tree died. Species known to be affected are Arizona ash (Fraxinus velutina) and Modesto ash (F. velutina ‘Modesto’). Raywood ash (F. oxycarpa) may also be affected. Arizona ash is native to Yavapai County and the other two are the primary ash species planted here. My first thought was an abiotic (environmental/non-living) cause since the problem was present in several trees but no apparent connection could be seen – many affected ash trees were growing next to unaffected ash trees. Upon seeing the symptoms, my first inclination was chemical injury as was evidenced by the small leaves. However, all involved assured me that no herbicides or other chemicals had been used near the trees. Once multiple reports were made and I talked at length with other tree owners, I ruled out chemical injury. In 2009, University of Arizona Cooperative Extension Plant Pathologist, Dr. Mary Olsen, and Forest Health Specialist, Arizona State Forestry Division, Bob Celaya and I went to the field and investigated several of the affected trees. Putting our heads together, we were not able to definitively diagnose the cause of decline in the affected ash trees. Our recommendations were to flood the irrigation basins (the trees were on drip systems). Strangely enough, many of the Prescott Valley trees have recovered and the dead material has been pruned out. A few have since died and been replaced. Fast forward to 2012 and again ash trees in Chino Valley and the Verde Valley are displaying the symptoms listed above. I am fairly certain we are seeing “ash yellows” also known as “ash decline”. Ash decline (AD) is caused by a phytoplasma, a bacterium that lives in the phloem (tissue that conducts the products of photosynthesis) and is transmitted (vectored) by phloem feeding insects such as leaf hoppers, spittlebugs, and psyllids. The AD pathogen is difficult to work with because it cannot be kept alive outside the plant in culture and diagnosis is done using molecular analysis. Some plant pathologists think that plant tissue used to produce grafted ash trees sold by nurseries may have been infected by the pathogen. Once an infected tree is fed upon by a suitable insect vector, it can transmit the disease to uninfected trees. The AD pathogen has been confirmed in Arizona (see additional references at the end of this column). Treatments for AD are not effective and it is recommended that seriously stunted trees be removed. However, until we confirm the disease, removal may not be warranted. I suppose the problem could have another cause, such as plant parasitic nematodes, but I tend to think that AD is the cause. It’s not easy or cheap to do the assays, but I will be looking for ways to conduct some sampling and analysis. Meanwhile, keep an eye out for symptoms of AD on your ash trees. If you notice the symptoms, inspect the irrigation system to make sure its functioning properly. If it seems under-irrigated, periodically irrigate the tree using a soaker hose or flooding a basin that extends outward from the trunk to the drip line of the canopy. This will ensure the problem is not caused by insufficient irrigation. There will certainly be more to come on this disease and I will keep you posted. Follow the Backyard Gardener on Twitter – use the link on the BYG website. If you have other gardening questions, call the Master Gardener help line in the Camp Verde office at 928-554-8999 Ext. 3 or e-mail us at cottonwoodmg@yahoo.com and be sure to include your name, address and phone number. Find past Backyard Gardener columns or provide feedback at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/. Host Range and Distribution of the Phytoplasma Causing Arizona Ash Decline (Journal of Arboriculture) http://joa.isa-arbor.com/request.asp?JournalID=1&ArticleID=202&Type=2 Ash Yellows (University of Wisconsin Extension) http://hort.uwex.edu/sites/default/files/Ash%20Yellows.pdf Ash Yellows (University of Illinois Extension) http://urbanext.illinois.edu/hortanswers/detailproblem.cfm?PathogenID=85  |