Common Plum Tree Diseases and How to Treat Them

Plum trees are a beautiful addition to any garden, providing delicious fruits for eating and baking. However, they can be susceptible to diseases that can damage or kill the tree. In this article, we will discuss some of the most common plum tree diseases and how to treat them.

Bacterial Canker Disease

Bacterial canker disease is caused by the bacterium Pseudomonas syringae. This disease affects the tree's bark, causing it to crack and develop sunken areas. The leaves and fruit may also show signs of infection, including brown spots and lesions. In severe cases, the tree may die.

To treat bacterial canker disease, prune infected limbs and branches at least six inches below the affected area. Disinfect pruning tools with rubbing alcohol between cuts to prevent the spread of the disease. Apply copper-based fungicides in the fall and winter when the tree is dormant. Proper care, including regular watering and fertilization, can also help prevent bacterial canker disease.

Plum tree with bacterial canker disease.

Black Knot Disease

Black knot disease is caused by the fungus Apiosporina morbosa. It appears as hard, black swellings on the tree's bark, which can eventually girdle and kill the branch or limb. The disease may also affect the fruit, causing it to become deformed and discolored.

To treat black knot disease, prune infected limbs and branches at least four inches below the affected area. Again, disinfect pruning tools with rubbing alcohol between cuts. Apply fungicide sprays containing copper or chlorothalonil in the spring before bud break and again after petal fall. Proper care, including pruning and fertilization, can also help prevent black knot disease.

Plum tree with black knot disease.

Leaf Spot Disease

Leaf spot disease is caused by various fungi that infect the leaves of the plum tree. Symptoms include small, dark spots on the leaves that can grow and merge together, eventually causing the leaf to drop prematurely. Severe infections can lead to defoliation and weaken the tree.

To treat leaf spot disease, rake up and dispose of fallen leaves and fruit to prevent the fungus from overwintering. Prune the tree to improve air circulation and reduce humidity. Apply fungicide sprays containing chlorothalonil or copper in the spring before bud break and again after petal fall.

Plum tree with leaf spot disease.

Peach Tree Borer

Although not technically a disease, the peach tree borer can cause significant damage to plum trees. The larvae of this moth burrow into the tree's trunk, causing extensive damage and weakening the tree. Symptoms include sap oozing from the base of the tree, wilting leaves, and dead branches.

To treat peach tree borers, apply insecticides containing chlorpyrifos or carbaryl in the summer and early fall when the adult moths are active. You can also use sticky bands around the trunk of the tree to trap the moths before they lay their eggs. Proper care, including fertilization and pruning, can also help prevent peach tree borer infestations.

Plum tree damaged by peach tree borer.

Plum trees are a valuable addition to any garden or orchard, but they require proper care to avoid diseases and pests. By understanding these common plum tree diseases and how to treat them, you can keep your trees healthy and productive. Remember to prune infected limbs, apply fungicides and insecticides, and provide proper care to prevent future infestations.

Bacterial Canker Disease, Black Knot Disease, Leaf Spot Disease, Peach Tree Borer