Plum Tree Diseases and Pests: Identification and Management Guide

Plum trees can be affected by fungi, bacteria, viruses and insects, but similar symptoms often have different causes. This guide owns the broad plum pest-and-disease topic. For yellow leaves, poor growth or failure to fruit without clear pest or disease signs, use our plum tree stress and fruiting guide.

Start with the symptom pattern

• Flowers or fruit turn brown and develop spores: investigate brown rot.
• Black, rough swellings on twigs or branches: investigate black knot.
• Small holes with reddish or purple margins: shot hole disease or insect feeding may be involved.
• Distorted, hollow or enlarged young fruit: consider plum pockets.
• Rings, mottling or unusual fruit patterns: seek diagnosis for a possible virus rather than treating by appearance alone.
• Sticky foliage, curled shoots or sooty mold: inspect for aphids or scale.
• Fine stippling, bronzing or webbing: inspect for spider mites.
• Larvae or crescent-shaped scars in fruit: identify the regional fruit-feeding insect before selecting a control.

Brown rot

Brown rot commonly affects blossoms, shoots and ripening stone fruit. Infected fruit may soften, develop tan or gray spore masses and remain as mummies. Remove mummified fruit and diseased material where local guidance recommends, improve airflow, avoid unnecessary wetting of flowers and fruit, and protect fruit from wounds. Fungicide timing and resistance programs vary by region and product label.

Black knot

Black knot produces elongated swellings that become hard, rough and dark. Confirm the symptom because normal callus growth, crown gall and other injuries can look different. Dormant pruning is a common management component, but cut placement and disposal should follow regional Extension guidance. Nearby unmanaged Prunus hosts can be continuing sources of spores.

Shot hole and other leaf spots

Shot hole symptoms begin as small lesions whose centers may drop out. Similar holes can result from insects or physical injury. Inspect lesion margins, twigs and fruit, and note when symptoms began. Sanitation, canopy management and carefully timed preventive treatments may be recommended after diagnosis.

Plum pockets

Plum pockets distort young fruit and can leave it enlarged and hollow. Remove affected fruit when practical and ask local Extension whether dormant or pre-bloom prevention is appropriate in your region.

Viruses and reportable concerns

Plum pox and other viruses cannot be diagnosed reliably from a web photograph. Do not propagate symptomatic material. If ring patterns, mottling or unusual fruit symptoms suggest a regulated disease, contact your state agriculture department or Extension diagnostic service promptly.

Common plum pests

• Aphids: curled tender growth, honeydew and sooty mold.
• Scale insects: fixed bumps on bark or foliage, sometimes with honeydew or weakened growth.
• Spider mites: stippling, bronzing and sometimes fine webbing, especially under hot, dusty conditions.
• Fruit-feeding insects: species and timing differ geographically; identify larvae, entry scars and damaged fruit locally.
• Borers: gum, frass or dieback around trunks and limbs can signal infestation or another bark injury.

Integrated management

1. Photograph symptoms and record when and where they began.
2. Inspect flowers, fruit, both leaf surfaces, twigs, trunk and root flare.
3. Correct irrigation, drainage, trunk injury and excess vigor that can compound damage.
4. Use sanitation and pruning practices matched to the diagnosed problem.
5. Conserve beneficial organisms and use the least-disruptive effective control.
6. Apply a pesticide only when its current label lists plum and the target pest or disease. Follow rates, timing, PPE, re-entry, preharvest and mixture directions.

Related plum resources

• Planting and growing plum trees
• Diagnosing yellow leaves, stress and poor fruiting
• Browse current plum trees

Regional pest cycles and legal product uses vary. Use current local Extension guidance and the product label.