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