Plum trees are susceptible to a number of diseases. Some attack the wood, while others attack the foliage or fruit. The severity of the disease and treatment method depend on the type of plum tree.
Many diseases cause damage to the leaves of fruit-bearing plum trees. Some of those infections include powdery mildew, caused by the Sphaerotheca pannosa and Podosphaera tridactyla fungi; prune dwarf virus, bacterial spot and plum pox virus.
Powdery mildew begins with areas of fungal growth that appear on the leaves and fruit. Prune dwarf virus is characterised by undersized, malformed leaf growth. Bacterial spot creates dark angular spots on leaves and fruit. The leaves turn yellow and fall, resulting in defoliation. Leaves infected with plum pox virus may have mild discolouration or light green rings. Fruit infected with pox virus falls from the tree.
Treat powdery mildew by spraying trees every two weeks while they are in full bloom. Alternate fungicides so that the fungus does not develop a resistance. Purchase cultivars that are resistant to prune dwarf virus. There is no treatment for bacterial spot; manage the disease by using chemical sprays. Destroy trees that are infected with plum pox virus.