Plum Tree Disease


A plum is a purple stone fruit tree with the appearance of a dusty, white coating of wax. Eaten fresh or used in making jams and jellies, plums are also fermented and used to make plum wine. Dried plums, called prunes, are a sweet treat with powerful antioxidants. High in fiber, prunes can also become infected with threatening diseases that will affect the fruit and overall growth of the tree.

Time Frame

Plum tree diseases strike during blossom time in the early spring when new fruit and twigs are beginning to grow. Spores and other fungi travel through the air to infect the new growth. When the tree has fruited, typically in the summer, insects can infest a plum tree and devastate its growth. During the early spring, it's important to carefully watch the plum tree for signs of disease and pests. Early treatment can prevent any stunting or the eventual death of your plum tree.

Black knot

The most serious disease of plum trees is the black knot fungus. The spores are released during blossom time and when new shoots have completed growth. Carried by the wind, the spores have a devastating effect on the tree. Black knot fungus forms hard black knots on the small branches of the tree. The knots are long and will kill the infected branches. Overtime, the growth will stunt the plum tree causing death. Remedying this disease is quite easy and can be done when pruning the tree. Prune 4-5 inches below the infected knot and apply a dressing to the large wound.

Brown Rot

Brown rot is a fungus of the plum tree that infects the blossoms and fruit of the tree. Small branches are also devastated and show signs of cankers, including rotting fruit. A powdery gray tuft envelops the twigs and fruit, especially when the tree is wet with moisture. To control brown rot, apply a fungicide during the blooming period in early spring. All of the fruit and cankered twigs remaining on the tree should be removed. Dead fruit on the ground that has been infected should be buried.

Plum Pox Virus

Plum pox virus began in Europe in the early 1900s, where it had devastating effects on plum trees. Caused by aphids that attack the fruit on the tree, plum box virus will produce irregular or deformed shaped fruit. When the aphids infest the fruit, the plums also develop a yellow or brown ring or blotch. The amount of plums on the tree is reduced over time and can slowly kill the tree if left untreated. To prevent plum pox virus, treat the trees with insecticide to reduce the number of aphids.


Always avoid pruning plum trees during the summer which can stunt the growth of the tree and effect the ability to fruit. Never prune in the winter or in cold and damp weather conditions, which can increase the chance of diseases, such as brown rot disease. When pruning or cutting off branches, always dispose of the cuttings to avoid transferring the disease to the rest of the tree or other surrounding trees.

Keywords: plum tree disease, black knot disease, plum pox virus

About this Author

Callie Barber has been writing professionally since 2002. Barber's love for design and writing inspired her to create Design Your Revolution, a blog that shares creative and affordable ways to decorate indoor and outdoor living environments. Her articles have appeared on and Barber holds a Bachelors of Arts in international studies from the University of North Carolina.