Q: I have three Arizona ash trees that are 10 years old. This past year they have looked like this (see photo). I have been trying to figure this out. I went to a few nurseries and got different answers and remedies: not enough water and not enough fertilizer. I water them once a week for one hour until I get over an inch of water in my rain gauge. I use shrub and tree fertilizer but I still have the problem. What is your opinion on this?
A: Your ash trees are displaying what is commonly called a witchβs broom. The normal growth of the tree has been interrupted, producing tiny leaves together in bunches from the same location we expect leaves. The causes of this are not always clear. Some possible problems could be a fungal infection, herbicide exposure or other environmental condition, mites feeding on the trees, and microorganisms called phytoplasmas that may be vectored by insects such as leafhoppers. In some cases, the trees will grow out of this and in others you might need to manage the situation. If you want me to examine a cutting for mites, etc., then please let me know.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com
