Diseases of mulberry (
Sooty canker is caused by the fungus Hendersonula toruloidea. Mulberry is very susceptible as are ash, citrus, walnut, fig, oleander, wisteria, sycamore, apple, apricot, chinaberry, poplar and other smooth or thin bark trees. Sooty canker causes cankers, wilting and dieback in tree branches. Leaves on affected branches are often small and wilt and die during the summer. Brownish, moist areas appear on limbs during the first stages of disease, and the bark in these areas cracks or peels away revealing black masses of fungal spores. The bark and sapwood around the spore mass is stained dark brown or black (photo 1), and sapwood under and around the canker is killed.
The pathogen infects the host only through cracks in the bark or wound sites such as those created by heat stress, sunburn, pruning or freezing. Trees with smooth bark that is easily wounded are particularly susceptible. Infection is thought to take place during mild wet weather in the winter months. Fungal spores easily move from one infection site to another by wind and rain, and infect new wound sites. The fungus grows into the bark where it becomes established and produces masses of black spores for which the disease is named. It is well adapted to hot, dry weather, and progresses in stressed trees during hot summer weather.
Disease can be prevented by maintaining tree vigor and avoiding unnecessary pruning or wounding. Sunburned bark is the most common point of entry for fungal spores, and careful pruning techniques should be used so that limbs that shade the trunk and scaffold branches are not removed.
When infections are found in upper branches, remove infected limbs by cutting at least six inches below infection sites. If severe pruning is needed, be sure to remove limbs in the fall or early spring when the remaining tree will not be sunburned as a result of pruning. Remove all infested plant material from the site since they are a source of spores.
February 21, 2013