Forest Health > Insects and Diseases publication
Diseases of... Hardwood Stem
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BRANCH AND STEM CANKERS OF SYCAMORE
Typical branch dieback in sycamore infected with the canker fungus Botryodiplodia theobromae.
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| Pathogens: |
Fungus Botryodiplodia theobromae
Other fungi including:
Dothiorella spp. (asexual stage of Botryosphaeria spp.),
Phomopsis spp. Hypoxylon tinctor, and Massaria platani |
| Common Host: |
American Sycamore Plantanus occidentalis |
Significance: |
Branch and stem cankers of sycamore are a common, readily visible, and sometimes lethal problem in many parts of Florida. Cankers are usually most prevalent and serious on trees which have been injured, by construction for example, or trees which have been exposed to certain environmental stresses such as extreme temperatures or drought. Many fungi are capable of causing cankers on sycamore, and it is common in Florida to find two or more fungi acting in combination. However, Botryodiplodia theobromae is perhaps the most common. Branch and stem cankers may well be the most serious disease affecting sycamores in Florida. |
Recognition: |
The most readily recognizable symptom of this disease problem is a localized branch mortality (i.e., in one portion of the tree's crown). In the very early stages of disease development the leaves on infected branches may be reduced in size, discolored, (yellow to brown), or shriveled. As infections advance typically from the upper to lower or smaller to larger branches, the crowns progressively thin, from the top down or inward from the outside. Close examination of infected stems or branches reveals typical cankers in the bark tissues (flattened or depressed areas due to the death of the cambium).
Cankers are usually elongated, often associated with branch stubs, and may be surrounded by distinct callus ridges at their margin. Callus ridges are usually indicative of older, inactive cankers. Young or actively growing cankers, on the other hand, are usually free of callus margins and may be more difficult to detect. The wood behind cankered bark tissues is usually dead, especially in older cankers, and presents a wedge or pie-shaped appearance when viewed end-on in cross-section.
Small, black fruiting bodies called pycnidia (sing., pycnidium; asexual stage) or perithecia (sexual stage), depending upon the particular fungus or fungi involved, are often visible on or near the diseased tissues. These fruiting bodies are generally about the size of a pin head and may appear to sit on top of the bark or to be partially embedded therein. The similarity between the fruiting bodies produced by many of the sycamore canker fungi usually makes microscopic examination of the spores produced within these structures a requirement for specific identifications. |
Infection Biology: |
The fruiting bodies of Hypoxylon tinctor are distinctive and readily recognizable. This fungus produces its spores in a dark brown to black, hard, crusty, structure called a stroma (pl., stromata) on the surface of stems and larger limbs. Stromata may reach as much as 15 cm in length.
Spores of the various canker fungi are spread by wind, splashing rain, insects, and sometimes man, to susceptible host tissues where they initiate new infections. Infections frequently begin at wounded or broken twigs or branch stubs, and then progress downward into larger limbs and eventually the main stem. In time, and under suitable environmental conditions, the fungi produce their characteristic spore-bearing structures (fruiting bodies) on infected trees, and the cycle continues. |
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Control: |
Damage resulting from sycamore cankers can be minimized by planting sycamores on sites with adequate moisture and nutrients. Timely irrigation in hot, dry weather reduces water stress and susceptibility to infection in urban and shade trees. Fertilizing sycamores to maintain good tree vigor is suggested. Prune cankered branches by cutting well below the advancing margin of cankers to limit spread in infected trees. Remove severely diseased trees and/or branches to reduce local inoculum (i.e., fungus available to initiate new infections) and avoid wounding sycamores, especially those under moisture or other environmental stress.
PHOTO: Pimple-like fruiting bodies of Botryodiplodia theobromae on an infected sycamore branch.
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Bulletin No. 196-A | Printed October, 1983 | Contact the Forest Health Section |
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