BOTRYOSPHAERIA CANKER
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.
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.
SEPTORIA CANKER
Septoria canker on young cottonwood saplings.
Septoria canker is caused by the fungus Septoria musiva. Although this is a disease of poplars, native poplar species are not severely attacked. However, this is an important problem wherever hybrid or introduced poplars are grown. With the ever-increasing emphasis on poplar planting, this will probably become a much more important problem in the near future.