The noticeable decline in many of our local ash trees is due largely to a disease known as Ash Yellows. It is caused by wall-less microbes, known as mycoplasmalike organisms, or MLOs, that are presumably spread by phloem-feeding insects such as leafhoppers. So it, too, has the effect of constricting the vessels that carry nutrients to the crown. Consequently, the leaves of an effected tree are often a pale green/yellow, and turn bright yellow prematurely in the fall. There can also be significant dieback in the crown. These symptoms mimic those of an EAB infestation. A major difference, however, is that this disease seems somewhat predicated on stressful environmental conditions, including excessive heat and drought. Keeping an ash tree healthy, therefore, can bolster it against this threat. But, of course, trees afflicted by Ash Yellows are far more susceptible to the EAB.