Bean Diseases

By The Old House Web

Bean Diseases

Root Rot

The symptoms vary with the causal organism but generally the plants wilt and die. The leaves turn yellow and drop off and plants are stunted. No chemical control is listed.

Halo Blight

Leaf symptoms are numerous dead spots with yellow halos. At high temperatures the halos may be absent and entire leaves may be killed as the bacteria moves systemically in the plant. Under humid conditions a cream colored ooze appears on the pods. The disease is favored by cool wet weather. Apply sprays of copper(1) fungicides.

Common and Fuscous Blight

Large dead areas occur on the leaves. They begin as small, water soaked or light green areas, which dry out, and turn brown with narrow yellow halos. Similar water soaked spots on the pods merge into irregular blotches. The disease is favored by warm weather. Apply sprays of properly labeled copper fungicides.

Syringae Blight

This disease is more common on lima beans. Small, reddish brown spots, with distinct margins form on the leaves. There may be darkening of veins on the lower leaf surface. As the spots enlarge, the center turns gray and drops out. Apply a properly labeled copper fungicide.


Black, sunken lesions, about 1/2 inch in diameter develop on pods, stems and cotyledons but are most prominent on pods. A salmon colored ooze, on lesions and the veins on lower leaf surfaces, turns black. On limas, symptoms are sooty appearing spots on leaves and pods. The spot margins are diffuse. The disease is spread by wind, rain, animals, workers, and implements. Disease development is favored by cool wet weather. Use sprays of Chlorothalonil(14) or copper.

Powdery Mildew

The first symptom is faint, discolored leafspots. Then a powdery growth spreads from the spot to other plant parts. Young leaves are dwarfed, curled, and may turn yellow and drop. The pods are dwarfed and distorted. The disease develops late in the season on mature plants. Sprays of sulfur(0) or copper(1) control this disease.


Plants are stunted and leaves are puckered, mottled, and stunted. The pods are sometimes distorted and stunted. The disease is spread by aphids and workers handling diseased plants then healthy plants. There is no satisfactory chemical control.

Gray Mold

A grayish powdery mold forms on the pods. The disease is favored by wet weather. Use Chlorothalonil(14), copper(1), or sulfur(7).

White Mold

Disease symptoms are white, cottony growths on pods and stems. Small, hard, black structures form in the white mold's growth. The rotted pods become wet and soft and plants affected by the disease often die. The disease is spread by wind. White mold often gets started in dying blossoms and injured tissues. Use Chlorothalonil(14), copper(1), or sulfur(7).


Disease symptoms are reddish dusty spots on the lower leaf surfaces and pods. Rust is most common on mature plants in the fall. The disease is spread by wind, workers, and implements. Rust can be controlled with sprays of Chlorothalonil(14) or sulfur(0).

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