Organic Control of Green Bean Pests: Slugs and Bean Beetles

Identifying the Culprit

Your description—1-inch seedlings devoured overnight, no visible insects—strongly suggests slugs. They feed at night, hide by day, and target tender new growth. The yellow "ladybug-like" beetles from prior years were likely bean leaf beetles (Cerotoma trifurcata), which chew holes in leaves but don't destroy entire seedlings.

Organic Slug Control

1. Coffee grounds barrier: Thick, continuous ring around plants (Starbucks gives free grounds). Reapply after rain.
2. Copper tape collars: Adhesive copper tape around pots/beds gives slugs a mild shock. Polish pennies work in a pinch.
3. Beer traps: Shallow dishes of beer (any cheap brand) attract and drown slugs. Place at soil level; empty daily.
4. Diatomaceous earth: Food-grade DE dusted around plants; reapply when wet. Less effective in humid conditions.
5. Hand-picking: Go out at night with a headlamp; drop slugs into soapy water.

Bean Leaf Beetle Management

• Crop rotation: Move beans to a new bed annually—breaks beetle lifecycle.
• Row covers: Lightweight fabric (Remay) over hoops excludes beetles until flowering.
• Kaolin clay (Surround WP): Spray on foliage; creates barrier that deters feeding.
• Beneficials: Encourage tachinid flies and parasitic wasps with nectar plants (alyssum, dill, yarrow).

Your compost-only approach is excellent—healthy soil grows resilient plants. Combine barriers, traps, and rotation for lasting control.