Roots of infected plants accumulate less starch then normal, and may even die. Ash yellows was first studied in forest stands in the northeastern U.S., where it kills many white ash, especially in the understory. Studies in the Upper Midwest and Great Plains have extended the known range of the disease as far south as the Ohio River, as far west as Utah and north to Alberta. In some Great Plains cities and windbreaks, more than half the green ash tested positive for the pathogen. While about 15 percent of green ash tested positive in Iowa, Wisconsin and Minnesota cities, the percentages in individual cities varied from zero to more than 30 percent.
Mystery still surrounds the question of how ash yellows spreads from tree to tree.
Insects in the leafhopper group are thought to transmit the phytoplasma from tree to tree, but hard evidence is still lacking. Management options for ash yellows range from slim to none. Antibiotic injections have been tried, with inconsistent results. Not at all. So while ash yellows is a cloud in the sky for landscape ashes, it's by no means a tornado.