Miscellaneous Cankers, Phomopsis scabra, (Sacc.) Traverso; Dothiorella sp.

Leininger, T.D; Solomon, J.D.; Wilson, A. Dan; Schiff, N.M. 1999. A Guide to Major Insects, Diseases, Air Pollution Injury, and Chemical Injury of Sycamore. Gen. Tech. Rep. SRS-28. Asheville, NC: USDA Forest Service, Southern Research Station. 44 p.

Importance.-These fungi cause cankers that are generally less of a problem than the canker fungi mentioned earlier in this guide. Phomopsis scabra and Dothiorella sp. can cause serious dieback and mortality when environmental conditions weaken the host.

Identifying the Disease.-Phomopsis scabra can cause cankers ranging from 10 cm to 1 m in length and may be mist taken for cankers caused by Botryosphaeria rhodina . Cankers of both fungi are usually associated with dead buds, terminals, or lateral branches (fig. 32). At first, cankers may go undetected until the disease has progressed enough to cause small, off-color leaves, branch dieback, or tree death. Cankers will become dark and sunken after 1 to 2 growing seasons.

Figure 32. - Phomopsis cankers on branches of a site-stressed.

Identifying the Fungi.-Both fungi form spores in small, light-colored, flaskshaped fruiting bodies (usually pycnidia) formed on host tissue. Phomopsis scabra conidia are colorless, spindle-shaped, or slightly curved single cells. Dothiorella spores are colorless, one-celled, and oval.

Biology.-Phomopsis scabra cankers seem to develop readily at temperatures below 24º C. Growth of Dothiorella cankers slows during the growing season allowing callus tissue to form. Spores of both fungi are spread by wind, rain, insects, and mechanical means. They enter through wounds.

Control.-Damage from these fungi can be reduced by preventing wounds and promoting tree vigor by planting on good sites.