Aphids

About this condition

Aphids are small sap-sucking insects that cluster on tender new growth and leaf undersides. They are common on bonsai from spring through autumn; left unchecked, they can weaken the tree and trigger sooty mold.

Common symptoms

• Clusters of green, black, or brown insects appear on new shoots and leaf undersides
• Leaves and stems become sticky from honeydew deposits
• Leaves curl and turn yellow
• Ants may be frequently observed on the tree

Common causes

• Rising temperatures from spring onward activating aphid reproduction
• Poor air circulation allowing colonies to establish
• Excess nitrogen fertilization producing tender, pest-attractive new growth
• Absence of natural predators such as ladybugs in the surrounding environment

Prevention (growing conditions & routine care)

Position trees with good air circulation and inspect new growth regularly for early detection. Avoid excess nitrogen fertilization. Be alert to increased ant activity on the tree, which often indicates aphid presence.

Related guide

When to see a vet

What can a nursery or grower do?

Specialist bonsai nurseries and growers can advise on management options appropriate to the severity of infestation and on environmental adjustments to prevent recurrence.

Related columns

• How to Choose a Bonsai Pot | The Basics of Matching Pots to Tree Species and Shape
• Leaf Pruning of Deciduous Bonsai (Hagari) — A Summer Technique to Promote Smaller Leaves and Finer Branching
• Beginner Bonsai: Year-One Growing Schedule by Species
• Bonsai Root Growth and Healthy Root System Development: Root Establishment Management and Repotting Timing

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