How to Identify Plum Tree Diseases

Good orchard management practices increase plum production.

Plum tree diseases can quickly destroy fruit crops or even kill the trees. Good sanitation can prevent many diseases Remove diseased fruit and wood on and around plum trees immediately. Keep organic insecticides and fungicides on hand and spray as soon as symptoms appear.

Things You'll Need

• Hand lens
• Pruners
• Pocket knife
• Lime sulfur
• Bordeaux
• Sprayer
• Hack saw
• Mirror with long handle
• Balanced fertilizer

Instructions

1. Look through a hand lens for black swellings or knots on smaller branches of the plum tree. These are evidence of black knot. Take off developing knots before flower buds open in spring by pruning branches 4 inches to 5 inches below the knots. Apply lime sulfur or Bordeaux at the site of pruning.

2. Inspect fruit, blossoms, spurs and shoots for rotted, brown spots. These are caused by brown rot. Remove and destroy remaining fruit, mummies and cankered twigs in late summer or fall. Spray trees with lime sulfur at bloom and continue spraying at 10 to 14-day intervals throughout the growing season.

3. Scratch oval-shaped swelling and callouses with a knife or fingernail and observe for gum-like texture. These are symptoms of perennial canker. Remove cankered wood and burn. Paint wounds on the tree with lime sulfur to prevent canker.

4. Cut the branch of any stunted trees which have light, dull leaves. Inspect the cut branch for a ring of discolored wood. The color can vary from gray to dark brown. Peel back the bark and look for discolored streaks in the wood. These are symptoms of verticillium wilt. There are no good treatments for verticillium wilt, but it helps to prune out affected wood, fertilize, and keep the tree properly watered.

5. Hold a mirror under the leaves of a plum tree and look for angular, water-soaked black or brown spots or "shotgun" holes. These are symptoms of bacterial spot. Apply a balanced fertilizer. Spray affected areas with Bordeaux.

Tips & Warnings

• For additional disease identification, take samples to your local agriculture extension office. You can also enter symptoms into online diagnostic keys, such as Cornell University Extension's key (see Resources).

• Always read and follow precautions and directions before mixing or applying chemicals.

References

• Disease Control in Cherries, Plums, and Other Stone Fruits
• University of California Integrated Pest Management: How to Manage Pests in Gardens and Landscapes
• Texas A&M University Extension: Home Fruit Production - Stone Fruit
• Purdue University Extension: Fruit Diseases

Resources

• University of Missouri Extension: Fruit Spray Schedules for the Homeowner
• Cornell: Diagnostic Key