
Michigan Ash
Disease Mystery Solved By Linda
McElreath January 28, 2002A fungal disease caused the demise
of ash trees in Michigans nursery stock last summer,
Agricultural Research Service scientists
have found. Ash trees became popular for street plantings in the United States after an
epidemic of Dutch elm disease killed thousands of elms in the early 1960s. But
in Michigan in 2001, young ash trees of the Fraxinus americana (Autumn
Purple) and F. pennsylvanica (Champ Tree, Cimmaron and Urbanite)
varieties began showing signs of disease in the form of smooth, round,
brownish-yellow cankers with distinct reddish, cracked margins. Although ash trees suffer from many insect and disease problems, arborists
in the region werent sure of the cause of the decline or why the problem
was centered in Michigan. Mycologist Amy Y. Rossman of ARS Systematic Botany and Mycology Laboratory in
Beltsville, Md., isolated a fungus found on the diseased trees. She and
colleague Lisa A. Castlebury used molecular sequencing to show that the fungus
was Phlyctema vagabunda, known primarily for causing bulls eye
canker of apples. P. vagabunda had been reported on various hardwood and
herbaceous hosts from temperate regions, but not on ash trees. The fungus leaves a characteristic round canker of dead bark that may become
discolored, sunken or cracked or may fall away altogether. Often the rest of
the branch beyond the canker dies or becomes much less productive. Cankers can
attack the bark of trees of all ages. Identifying the P. vagabunda fungus as one already present in the
United States reduced fears that it might have been brought in from outside the
country and could spread even further, or that it would prevent other countries
from accepting certain U.S. agricultural products. ARS identification of the pathogen is the first step toward developing
control measures to slow or prevent the decline of ash trees in Michigan. ARS is the chief scientific research agency of the
U.S. Department of Agriculture. Story contacts Systematic Botany and Mycology Laboratory Linda R Tokarz U.S. Department of Agriculture |