Importance. -- L. theobromae, can cause cankers and dieback in oak species over a wide geographical area. It is a potentially destructive pathogen under certain adverse environmental conditions, especially if trees are somewhat stressed.

Identifying the Fungus. -- Black, stromatic fruiting structures of the fungus develop on bark over the cankers. However, microscopic examination of spores is necessary for correct identification. Mature spores are dark, two-celled, and elongate.

Identifying the Injury. -- It is difficult to identify the canker by symptoms alone. Therefore, the fungus must be isolated and identified. Active cankers on trees with rough bark can be detected only after removing bark to expose dead cambium. Old or inactive cankers appear sunken and are surrounded by callus tissue. Dieback is frequently caused by L. theobromae, but can be confused with injury resulting from other diseases or stress conditions (figure 65).

Biology. -- The biology of Botryodiplodia cankers in oaks is poorly known. However, the cankers are favored by high temperatures. Cankers and dieback can develop rapidly in stressed trees. Fungal spores are spread by the wind and insects.

Control. -- Cankers can be minimized by preventing wounds, pruning cankered and dead limbs to reduce inoculum, and maintaining tree vigor when possible.