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Plum Tree Diseases and Pests

Plum trees are grown across the globe. They are adored for their ability to produce lush, juicy fruit. There are more than 200 cultivars. Out of these many cultivars are two main types, European and Japanese. Japanese plums are larger in size but European plums are sweeter because of their high sugar concentration. Plum trees tend to be susceptible to several diseases and a few pests. Proper maintenance of the tree and early intervention can successfully stop the spread of disease and eradicate known pests.


Aphids are a common pest on plum trees. These tiny green and black insects feed by attaching their mouths to leaves, buds, stems or the new growth of the tree. Once the aphids mouth is attached it begins sucking the sap, which is also called phloem. Phloem is the rich sugary, mineral rich substance that flows through trees and plants. It is in essence the trees blood. Aphids especially enjoy sucking the sappy phloem from new growth because it is tender and easy to penetrate with their mouths. Aphids will not kill a plum tree but they can weaken it if the infestation is severe enough.

Aphids can be managed by hosing the tree off with a high-pressure sprayer. Do this every other day. A gardener can also mix 25 percent dish soap with 75 percent water in a hand-held sprayer and spray the aphids. Aphids breathe through their skin and dish detergent suffocates them. Chemical sprays are available at garden centers. Follow the instructions on the label. There are insects that feed on aphids. Gardeners can purchase ladybugs at local garden stores to set loose on the plum tree for aphid maintenance and eradication as well.


Bacterial canker often attacks plum trees. Watch for depressions in the bark at the base of limbs in the fall. These depressions will grow quite large when spring arrives. They will quickly encompass the entire branch and the branch will perish.

All disease must be removed by cutting the branch off and cutting away the diseased wood until you reach healthy wood. Purchase a canker paint that is suitable for plum trees at any garden center. Paint the canker paint onto the wound. Spray the plum tree in August, September and October with copper based fungicide to prevent more canker spots.


Rust first appears on the underside of the leaves of the plum tree as small brown spots. Any leaves that appear to be affected by rust should be plucked from the tree and promptly destroyed. Prevent infestation by raking and disposing of all leaves around the base of the tree. Make sure the plum tree has been pruned to allow air flow through the branches. Rust flourishes in wet conditions, so by allowing air flow in the leaves, they will not be as susceptible to a rust outbreak.

Red Spider Mites

Red spider mites are common on plum trees. You will notice leaves that start to turn dry and brown. Look for a fine webbing on the leaves. Look closely for the tiny red spiders that tend to be on the underside of the leaves. These are common garden pests.

Spider mites have become resistant to virtually all insecticides that are available to the public. The best way to treat the spider mites is to spray the tree every other day using a hose with a strong water sprayer. Focus on the areas of mite infestation. Water can easily manage spider mites.

Plum Sawfly

The plum sawfly lays eggs on flowers during the spring. Once the flowers produce fruit, the eggs hatch and the maggots tunnel into the fruit. A gardener can look closely at the new fruit for tiny holes, which are an indication of maggot infestation. When the damage to the fruit becomes widespread, the holes will ooze a dark fluid.

Prevent the adult sawfly from living to lay their eggs by digging up the soil around the plum tree in the fall. Adult sawfly pupae winter in the soil at the base of the trees. By turning up the soil and exposing the pupae to the cold fall nights, they will die and be unable to lay eggs in the spring. Birds will also feed heavily on the exposed pupae. In the spring, spray the tree with derris insecticide, which can be purchased at a garden center. Spray the tree when the flower petals begin to fall. This will kill the eggs and larvae before they have a chance to infest the young fruit.

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