Hydrangea Rust and Spider Mites: Diagnosis and Organic Control

Hydrangeas with rusty, drying blossoms in full sun may have spider mites, especially in hot, dry weather. Check leaf undersides for tiny moving dots (size of a period) and fine webbing.

Spider Mite Confirmation

• Use a magnifying glass to inspect leaf undersides.
• Tap a leaf over white paper—mites appear as tiny specks that crawl.

Organic Control

1. Water spray: Blast leaf undersides daily with a strong hose stream to dislodge mites.
2. Predatory insects: Release ladybugs (especially Stethorus spp., “spider mite destroyers”) and lacewings. They stay where prey is abundant.
3. Avoid pesticides/fungicides: These kill beneficial predators and worsen outbreaks.
4. Increase humidity: Mist foliage; mites hate moist conditions.

For reference, see the Alabama Extension guide on hydrangea diseases (aces.edu) and the spider mite control article (helium.com). With consistent water sprays and beneficial insects, mite populations crash quickly.