Why Are There Spots on My Bean Leaves?

Spots on bean leaves are almost always a symptom of disease — bacterial or fungal infection producing localised dead tissue. The three most common diseases causing leaf spots on beans in UK gardens are halo blight (bacterial), bean rust (fungal), and anthracnose (fungal). Each produces a distinct spot type with a characteristic appearance that makes identification straightforward once you know what to look for. Getting the identification right matters because the management approach differs between bacterial and fungal causes.

Halo blight — water-soaked spots with yellow rings

Halo blight (Pseudomonas syringae pv. phaseolicola) produces small, water-soaked, greasy-looking spots that develop a characteristic pale yellow or cream halo around a brown central lesion. The halo is caused by a toxin (phaseolotoxin) produced by the bacteria that inhibits chlorophyll production in surrounding cells. Spots may appear anywhere on the leaf and can coalesce in severe infections. Stems develop elongated dark lesions and pods have sunken, dark marks. Halo blight is seed-borne and spreads by rain splash. Remove and bin affected plants; never save seed from diseased plants.

Bean rust — orange-brown powdery pustules

Bean rust (Uromyces appendiculatus) produces raised, brick-red to orange-brown powdery pustules on both leaf surfaces, typically on the underside first. Early stages show pale yellow spots on the upper surface with corresponding rusty powdery eruptions below. In severe infections the pustules coalesce and leaves turn yellow and fall. Rust is a fungal disease that spreads rapidly by airborne spores in warm (18–25°C), humid conditions. Remove affected leaves promptly; improve airflow; choose rust-resistant varieties in future seasons.

Anthracnose — dark brown spots with darker margins

Anthracnose (Colletotrichum lindemuthianum) produces dark brown, angular spots bounded by leaf veins, often with a water-soaked margin, primarily in cool, wet conditions. It also causes dark, sunken lesions on pods (the key diagnostic site) and stems. It is seed-borne, so buying certified disease-free seed is the primary prevention. Remove and bin affected plant material; practice a three-year rotation.