Why Are There Dark Sunken Spots on My Bean Pods?

Dark, sunken, reddish-brown to black lesions on bean pods — often with a slightly sticky or gelatinous appearance in the centre of each spot in wet conditions — are the characteristic pod symptom of anthracnose, caused by the fungus Colletotrichum lindemuthianum. Anthracnose affects leaves and stems as well as pods, but the pod symptoms are the most distinctive and most commonly noticed at harvest. The disease is seed-borne, meaning infected seed is almost always the original source when it appears in a garden.

Identifying anthracnose

Pod lesions are sunken, roughly circular or irregular, dark brown to black, and may show pink or salmon-coloured spore masses in the centre during wet conditions — this is diagnostic. Leaf symptoms are brown, angular spots bounded by leaf veins, usually with a water-soaked margin in early stages, particularly on the underside. Stem lesions are elongated, dark, and sunken. The disease is most severe in cool (13–26°C), wet conditions with frequent rain; hot, dry weather slows or halts progress. Once pods develop clear symptoms, the beans inside are often discoloured and unpalatable.

Are anthracnose-affected pods edible?

Pods with small, early spots on the outer surface may have unaffected beans inside — open them and check. Beans inside that are normal-coloured and firm are fine to eat. However, in heavily infected pods where lesions are large and penetrating, beans inside will be discoloured, shrivelled, or show brown marks — discard these. Harvest and inspect all pods promptly when anthracnose is present; the disease progresses rapidly in wet weather and pods that looked borderline can deteriorate within a day or two.

Prevention

Source seed from reputable suppliers with disease-free certification. Practice a minimum three-year rotation. Remove and bin all plant debris at the end of the season — the fungus can persist on infected stems in the soil. Avoid overhead watering. In gardens with a history of anthracnose, choose resistant varieties where available (check seed catalogue descriptions).