_Botryosphaeria ribis_ causes cankering and mortality of more than 50
woody plants. The fungus is widely distributed throughout the eastern
one-half of the United States. The pathogen infects the following
economically important hosts: sweetgum, redbud, willow, poplar, tupelo,
pecan, and hickory.
[Illustration: Botryosphaeria canker on sweetgum.]
The fungus gains entry into susceptible hosts primarily through wounds
or dead and dying twigs. Small oval cankers on stems or branches are the
first symptoms of infection. As the fungus continues to attack and kill
the cambium, the sunken cankers enlarge, eventually girdling and killing
the branch or stem above the cankered area. In the spring and early
summer, cankers on living portions of the host often produce an exudate.
Infected sweetgums generally produce the exudate in great quantities, to
which the common name of bleeding necrosis has been applied.
Reproductive structures called stroma are produced by the fungus on dead
cankered stems and branches during moist periods of the spring and
summer.
No practical method of control is known. Diseased trees seldom recover.
Infection of high value shade and ornamental trees may be prevented to
some degree by avoiding mechanical damage. Dead limbs and branches
should be pruned and wounds covered with a suitable tree paint. Infected
trees should be removed and burned.