Prepared by Nancy Doubrava, HGIC Horticulture Specialist, and James H. Blake, Extension Plant Pathologist, Clemson University. Revised by Joey Williamson, HGIC Horticulture Extension Agent.(New 05/99. Revised 04/04.)
Beans and Southern peas, including cowpeas, black-eyed peas and crowder peas, are commonly affected by many diseases in the home garden. Many of these problems can be successfully avoided by following recommended cultural practices.
Bean pods with black, sunken lesions or reddish-brown blotches most likely have anthracnose, a fungal disease caused by Colletotrichum lindemuthianum. Black, sunken lesions about ½ inch in diameter develop on stems, pods and seedling leaves (cotyledons) but are most prominent on pods. A salmon-colored ooze on lesions and the veins on lower leaf surfaces turns black. On lima beans, symptoms are sooty- appearing spots on leaves and pods. Anthracnose develops primarily during the spring and fall when the weather is cool and wet, and not during our hot, dry summers. Lima beans are particularly susceptible.
Prevention & Treatment: Prevent this disease by using certified disease-free seed for planting and removing all plant debris after harvest. Anthracnose can survive in the soil for two years on plant debris or be brought to the garden on infected seeds. Do not plant bean seeds in an area that had disease for two to three years. Avoid overhead watering and avoid splashing soil onto the plants when watering. Fungicide sprays of fixed copper are the only recommended chemical that can be used on lima beans for anthracnose control. Either fixed copper or chlorothalonil can be used on snap or pole beans. Wait seven days between spraying with chlorothalonil and harvest. Apply according to directions on the label.
Many fungi, including Rhizoctonia solani, Pythium species and Fusarium solani, form species phaseoli, live in the soil and will infect young seedlings or the seeds of bean plants. Seedlings fail to emerge after planting when the seeds rot in the soil or young seedlings may be stunted. Plants are usually affected slightly above or below the soil line with a watery soft rot. Roots of the plant usually die and leaves turn yellow.
Prevention & Treatment: Do not plant beans in low, poorly drained areas. Plant on raised beds. Plant after the soil has warmed to 69° F at a 4 inch depth. Reduce disease buildup in the soil by rotating locations in the garden where you plant bean or pea with other vegetables. Try to avoid injury to the root system, which often occurs during planting, through cultivation or due to a large population of nematodes in the soil. Remove crop debris immediately after harvest. Plant seeds previously treated with captan. Apply chemicals according to directions on the label.
|Lima Bean||'Jackson Wonder-AR'||Partially resistant to anthracnose.|
|Pole Bean||'Kentucky 191'||Resistant to rust.|
|Resistant to Bean common mosaic virus.|
|Southern Pea||'Mississippi Silver,'
|Resistant to Black-eyed cowpea mosaic virus and Fusarium wilt.|
Bean rust is mainly a disease of bean leaves that causes rust-colored spots to form on the lower leaf surfaces. Severely infected leaves turn yellow, wilt, and then drop off of the plant. Stems and pods may also be infected. This disease is caused by the fungus Uromyces appendiculaters. It affects most types of beans under humid conditions.
Prevention & Treatment: The fungus survives the winter in the soil, on plant debris and even on poles used the previous year. In gardens where rust has been severe, crop rotation is important. As plants begin to bloom, sulfur or chlorothalonil can be sprayed weekly on snap and green beans only. Do not apply chlorothalonil to lima (butter) beans. Wait seven days between spraying and harvest when using chlorothalonil on beans, and 14 days on Southern peas. Apply chemicals according to directions on the label.
There are two widespread bacterial blights that affect most types of beans, common blight (Xanthomonas campestris pathovar phaseoli) and halo blight (Pseudomonas syringae pathovar phaseolicola). The stems, leaves and fruits of bean plants can be infected by either disease. Rain and damp weather favor disease development.
Halo blight occurs primarily when temperatures are cool. Light greenish-yellow circles that look like halos form around a brown spot or lesion on the plant. With age, the lesions may join together as the leaf turns yellow and slowly dies. Stem lesions appear as long, reddish spots.
Leaves infected with common blight turn brown and drop quickly from the plant. Common blight infected pods do not have the greenish-yellow halo around the infected spot or lesion. Common blight occurs mostly during warm weather.
Prevention & Treatment: Both of these diseases come from infected seeds. The diseases spread readily when moisture is present. Avoid overhead watering and do not touch plants when the foliage is wet. The bacteria can live in the soil for two years on plant debris. Do not plant beans in the same location more frequently than every third year. Buy new seeds each year. Fixed copper can be applied at ten day intervals. Wait one day between spraying and harvest.
Mosaic viruses in which the leaves show sharply defined patches of unusual coloration may occur in beans. The causal agents of these symptoms may be nutrient imbalance or herbicide injury or result from infection by one of several viruses. In South Carolina viruses commonly found infecting beans are Bean yellow mosaic virus, Bean common mosaic virus and Clover yellow vein virus. Southern peas can be infected by Cowpea aphid-borne mosaic virus, Bean common mosaic virus and several others. It is not possible to distinguish between the viruses based on symptoms alone. Laboratory tests (ELISA) are required to identify the viruses and confirm that they may be responsible for the mosaic symptoms.
Prevention & Treatment: There are no recommended chemical controls for these problems. Many of these viruses are transmitted by aphids and are also transmitted through seed. For this reason it is unwise to save seeds from year to year.
Leaves are covered with patches of a whitish to grayish powdery growth. This disease is caused by the fungus Erysiphe polygoni. New growth appears contorted, curled or dwarfed and may turn yellow and drop. Pods are dwarfed and distorted. This is mostly a problem on fall beans. Powdery mildew is spread by wind and rain.
Prevention & Treatment: Avoid crowding plants by allowing adequate space between rows. On Southern peas, sulfur can be used. When the disease is first noticed, sprays or dusts of sulfur are recommended for use on snap and green beans only. Do not use sulfur on young plants. Apply chemicals according to directions on the label.
This fungal disease, caused by Cercospora species, occurs primarily on the lower leaves of plants as irregular, tan spots. Severe infection causes excessive leaf drop and stunting of the plant. Infection is worse during periods of extended rainfall, high humidity and temperatures between 75 to 85° F.
Prevention & Treatment: Use disease-free seed for planting. Remove all debris in the garden after harvest. Do not plant beans in the same area for two to three years. There are no resistant varieties or recommended chemicals for this disease in the home garden.
Small, soft, watery spots that are caused by the fungus Sclerotinia sclerotiorum occur on the stems, leaves and pods of beans. These spots enlarge rapidly under cool, moist conditions, and run together, girdling the stem. Infected pods turn into a soft, watery mass, before dying out and turning brown. Soon infected areas are covered by a white fungal growth.
Prevention & Treatment: Improve air circulation between plants and rows. Too much fertilizer favors heavy vine growth, creating areas for the disease to develop. There are no recommended chemical controls for the home garden.
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This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.