Plum trees are susceptible to various diseases.
Plum trees are susceptible to some pests and diseases and require regular maintenance. Fruit trees need to be fertilized and sprayed with fungicides and pesticides to promote strong, vigorous growth. Some of the most common diseases of plum trees caused by fungal infections are black knot, brown rot, powdery mildew, verticillium wilt, perennial canker, and plum bags. Bacterial diseases that affect plums are crown gall, bacterial spot, and bullet hole. Plum diseases, such as smallpox virus and rust, are caused by pests such as aphids.
Black knot, which is caused by the fungus Dibotryon morbosum, causes long, hard black knots to appear on the branches of the plum tree and sometimes on the main trunk. Perennial canker is a similar fungal infection caused by the fungi Valsa cincta and V. leucostoma and causes oval cankers to appear on the branches and trunk. In both cases, the knots and canker eventually engulf the tree and kill it.
The brown rot fungus grows in brown tufts on plum blossoms, berries, and small branches, causing blossoms to wilt and berries to rot. Many destroyed fruits are also damaged by the taphrina fungus, which creates hollow, enlarged spaces known as plum pockets in plum fruit. The fungus Podosphaera oxyacanthae causes powdery mildew, a white powdery growth on the underside of plum leaves that destroys the leaves and prevents the tree from growing. Verticillium wilt, caused by the fungus Verticillium alboatrum, also stunts plant growth, causing leaves to wilt, wood to discolor and roots to rot.
Crown gall infection, which is caused by the bacterium Agrobacterium tumefaciens, produces corky growths in plant tissue. The other two bacterial diseases of plum, bacterial leaf spot and bullet hole, are caused by the bacteria Xanthomonas pruni and Pseudomonas syringae. Spots and holes appear on the plum leaves, and the leaves turn yellow and fall off. Bacterial infection also produces holes in developing fruits, causing them to rot. Aphids spread the pox virus and plum blight. In the first case, fruit production is affected with the development of plums that become deformed or rotten, and in the second case, the leaves of the plums turn silvery, curled, and withered.
Fungal infections are wind- or soil-borne, while bacterial and viral infections can be soil- or pest-borne. To mitigate plum disease, this will help avoid planting a plum tree in a previously affected area. When caring for an already infected plum tree, it will be necessary to prune and burn diseased parts and spray the tree with fungicides, bactericides and pesticides. It is important to note that fungicides work primarily as preventatives and may not have much of an effect on severely infected trees.
