Battling Spider Mites on Angel Trumpets: A Biological Approach

The Spider Mite Challenge

Three mature angel trumpets (Brugmansia) brought indoors for winter are infested with spider mites: leaf drop, webbing in leaf axils, and long silken threads. The owner previously used systemic fertilizer/insecticide outdoors.

Why Systemics Are Harmful

Systemic insecticides kill beneficial predators (ladybugs, predatory mites, fungi) that naturally control spider mites. Outdoors, these predators keep mites in check; indoors, their absence allows mite populations to explode in warm, dry conditions.

Indoor Control Strategy

• Increase Humidity: Wash leaves and stems 2–3 times daily; use a humidifier. Cool, humid conditions slow mite reproduction.
• Stop Fertilizing: Nitrogen-rich fertilizers produce amino acids that mites love.
• Biological Control (Next Summer): Release ladybugs or apply Beauveria bassiana (e.g., Naturalis-O) as a fungal biopesticide.

Health Note

Spider mites are known allergens linked to asthma, hay fever, and contact urticaria.

Summary

Indoors: water frequently to raise humidity. Outdoors: rely on biological controls. Avoid chemicals with skull-and-crossbones labels.