Bt vs Spinosad for Caterpillars
| Feature | Bacillus thuringiensis (Bt) | Spinosad |
|---|---|---|
| Tier | Tier A | Tier A |
| Type | Microbial | Microbial-derived |
| Safety | Safe | Caution |
| Bee Safe | ✓ Yes | ✗ No |
| Pet Safe | ✓ Yes | ✓ Yes |
| OMRI Listed | ✓ Yes | ✓ Yes |
| Residual | 5-7 days on leaf surface; degrades rapidly in UV light | 7-14 days on leaf; breaks down in sunlight within 1-2 days on exposed surfaces |
| Best For | Caterpillar control on vegetables, fruit trees, and ornamentals. Mosquito larvae in standing water (Bti). | Thrips, leafminers, caterpillars, and fire ants. Broad-spectrum organic workhorse. |
Verdict
Bt is bee-safe and caterpillar-specific; spinosad is faster but requires evening application. Rotate both.
Full Guide: Bacillus thuringiensis (Bt)
Bacillus thuringiensis (Bt) is the most proven organic caterpillar control available. This naturally occurring soil bacterium produces proteins that destroy caterpillar gut linings within 24-72 hours while remaining completely safe for bees, pets, and beneficial insects.
Full Guide: Spinosad
Spinosad is a naturally derived insecticide that kills thrips, caterpillars, leafminers, and fire ants through nervous system disruption. OMRI-listed and effective, but must be applied in evening hours to protect pollinators.