What diseases can affect beans? Listed below are five diseases that most frequently occur on beans. Symptoms are described briefly. Colored pictures of disease symptoms can be seen in the publication "Identifying Diseases of Vegetables" available from the Penn State Publication Distribution Center, or from County Extension offices.
Anthracnose: Black, oval, sunken cankers develop on pods, stems, and cotyledons. Dark discolored areas may develop on veins.
Bacterial Blight: Dead spots and blotches, sometimes with a yellow halo, develop on leaves. On pods, water-soaked areas appear during wet periods and later become brownish as they dry.
Mosaic Viruses: On mosaic affected plants, young leaves may be stunted, curled, and mottled; yellowing may be distinct within mottled leaves. Pods can be distorted, blotchy with dark and light green, and in severe cases, have bronze blotchy areas.
Root Rots: Dark rotted areas, usually dry, can appear anywhere on roots and also on the stem near the soil surface. Some of the rots can kill young plants, but usually affected plants are stunted with yellowish leaf margins. Sometimes the root rot fungi attack seeds before or during germination, especially when germination is slowed by unfavorable conditions.
Downy mildew of Lima Beans:
A white downy mold develops on pods during moist conditions below 85 degrees farenheit. Affected areas on the pods are killed, and young shoots can be distorted.
Disease Control Program:
(1) When possible, use varieties with resistance to mosaic viruses.
(2) Start with pathogen-free seed from well-known seed companies. Bacterial blights, anthracnose, and some mosaic virus diseases can be introduced with seed.
(3) Rotate beans within the garden.
(4) Avoid planting beans near gladiolus if mosaic virus has been a problem in past years. Gladiolus is a source of one mosaic virus which can be carried to beans by aphids.
(5) Seed in well-drained soil after soil has warmed sufficiently to promote rapid seed germination and plant growth. Seed rots and root rots become severe when seed germinates slowly and plants grow slowly in cool soil.
(6) Do not provide excessive nutrients in fertilizer or manure. Excessive nutrients can result in rank growth and slow drying of plants, which can promote pod rots during extended wet periods.
(7) Try to prevent aphid problems near and in the garden. Aphids pick up and carry viruses; when feeding, they can put a virus into a plant within 1 minute.
(8) Do not work in bean plantings when leaves are wet. If bacteria that cause blights are present on any of the plants, the bacteria become sticky when wet, and can be spread on hands, tools and clothing.
(9) As soon as harvest is complete for any planting, pull and discard or compost the plants. When old plants are left in the garden, pathogens continue to multiply on them, and become an important source of inoculum that can result in more disease later during the current season, or can survive in the soil and initiate disease in future seasons.
Dr. Alan A. MacNab, Professor, Plant Pathology
Penn State College of Agricultural Sciences
211 Buckhout Lab, University Park, PA 16802
Loaded: June, 2003; AAM
Where trade names are used, no discrimination is intended
and no endorsement by the Cooperative Extension Service is implied.
Information provided is intended for consideration by the user, but is not
intended to be a recommendation. Production decisions should be based on
consideration of many types of information (scientific, experiential, economic,
legal, etc.) available to the user.