Botryosphaeria Canker
From Bugwoodwiki
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Importance
This fungus attacks many species of woody and herbaceous plants worldwide. In the South, B. rhodina causes cankers, dieback, and mortality in natural stands and plantations.
Identifying the Disease
Cankers, ranging in length from a few centimeters to several meters, form on twigs, branches, and main stems. Young and active cankers may be hard to see until sections of bark die revealing canker margins and fruiting bodies breaking through the bark (fig. 29a). Old, inactive cankers appear sunken and are typically surrounded by a callus ridge (fig. 29b). Dieback occurs above plant parts girdled by a canker.
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| Figure 29a. - Active Botryosphaeria canker on a sycamore stem. |
Identifying the Fungus
The asexual form of the fungus, Lasiodiplodia (=Botryodiplodia) theobromae (Pat.) Griffon & Maubl.) occurs more commonly than Botryosphaeria rhodina. Many black, pinpoint-sized pycnidia occur in groups, sometimes in rows, aligned with the wood grain. As the fungus advances in the sapwood, it causes a dark stain that can be seen beneath the bark and in cross sections of the stem.
Biology
Conidia typically enter wounds made by cultivating, harvesting, or insects. Canker formation and disease development are enhanced by stress from drought, poor site conditions, or other diseases such as a wilt or canker stain. Cankers grow faster, and seedlings are killed more quickly at warmer temperatures (30-35 º C).
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| Figure 29b. - Inactive Botryosphaeria canker surrounded by callus on a sycamore stem. |
Control
Promoting tree vigor by planting sycamores on good sites and avoiding dry, sandy sites should reduce the incidence of Botryosphaeria cankers. Pruning ornamental sycamores and thinning or harvesting plantations (where regeneration is by coppice growth) should be done in the fall and winter (temperatures < 20 º C) when the fungus is less active.
References
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.
