Why Are There Holes in My Bean Leaves?

Holes eaten through bean leaves — whether large, irregular tears or small, round perforations — are caused by insects or molluscs feeding on the leaf tissue. The size, pattern, and location of the holes, combined with any visible trail evidence (slime trails, frass), identifies the culprit. On established bean plants, moderate leaf damage from most pests does not significantly affect yield — beans can tolerate considerable defoliation if they are otherwise growing well. The concern is when whole leaves are consumed or when damage is concentrated on flower buds and pods rather than leaves alone.

Slugs and snails — jagged irregular holes

The most common source of large, irregular holes in bean leaves is slugs and snails. They feed primarily at night and leave a silvery slime trail on leaves and soil. Young plants (the first two to three weeks after transplanting or germination) are the most vulnerable — at this stage, complete defoliation is possible overnight. Slug pellets (iron phosphate-based pellets are safe for wildlife and pets), beer traps, copper tape around pot rims, and hand-picking after dark are all effective. Older established plants tolerate slug feeding much better.

Caterpillars — large, scalloped holes

Various moth caterpillars feed on bean leaves, particularly from midsummer onward. They create large, scalloped holes and leave dark spherical frass pellets on leaves beneath. Check the undersides of leaves and the stem bases for caterpillars. Hand-picking is effective for small infestations. Biological control with Bacillus thuringiensis (BT) spray is effective on young caterpillars and is widely available from organic suppliers.

Capsid bugs — small holes with tattered appearance

Common green capsid (Lygocoris pabulinus) causes clusters of small, irregular holes that start as pinprick punctures and expand as the leaf grows, creating a tattered, riddled look. The actual pest is rarely visible — it drops at the slightest disturbance. Capsid damage on mature leaves rarely affects yield significantly. Encouraging hedgerows, long grass margins, and flowering plants around the plot supports the predatory insects that limit capsid populations.