Spider Mite Infestation on Butterfly Bush: Biological Control Beats Chemicals

A Textbook Spider Mite Crisis

A gardener near Washington DC has battled spider mites on butterfly bushes for 5 years. Bonide Mite Spray (containing malathion, lindane, carbaryl, kelthane) worked briefly but mites returned stronger. Weather: hot, dry, humid – perfect for mites.

Why Chemicals Fail

• Insecticides kill natural predators (ladybugs, predatory thrips, mite‑eating mites, fungi).
• Carbaryl (Sevin) actually increases mite damage by eliminating predators.
• Spider mites reproduce in 5 days at 100°F; predators can’t keep up in hot, dry air.

The Biological Solution

• Predatory mites: Phytoseiulus persimilis and Neoseiulus fallacis specialize in eating two‑spotted spider mites. They need ≥60% humidity; mist plants several times daily to maintain it.
• Ladybugs and lacewings: Good backup, but may not match mite reproduction speed.
• Water blasting: Spray undersides of leaves 2‑3 times daily to physically remove mites while waiting for beneficials.
• Fungal biocontrol: Beauveria bassiana (Naturalis‑O) infects and kills mites; requires thorough spray coverage.

Sources for Beneficials

Buglogical, Worm’s Way, Kuida Agricultural, Growquest, Futuregarden – all mail‑order.

Critical Advice

Stop chemical sprays immediately. They destroy the very predators that could control mites long‑term. Establishing a predator population may take 2‑3 years if chemicals have been used heavily.