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.
- Plant certified seed or seed of known high quality that has been treated with a fungicide.
- Select resistant varieties for planting.
- Rotate the location in which beans are planted in the garden.
- Plant beans in a well-drained area and avoid overhead watering.
- Remove bean debris from the garden after harvest, since this is where some disease-causing agents can survive the winter.
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. Lesions may develop salmon-colored ooze, and the veins on lower leaf surfaces turn 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 copper fungicides or chlorothalonil can be used on snap or pole beans. Wait seven days between spraying with chlorothalonil and harvest, and one day between spraying a copper fungicide and harvest. Chlorothalonil and copper fungicides both give fair control of anthracnose. Spray chlorothalonil at 7-day intervals and copper fungicides at 10-day intervals. Apply according to directions on the label.
Bean Root Rots
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 the leaves turn yellow.
Prevention & Treatment: Do not plant beans in low-lying, poorly drained areas. Plant beans 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 (a fungicide).
Table 1. Some Disease Resistant Varieties for South Carolina.
|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. Chlorothalonil gives excellent control of rust, and sulfur gives good control. Spray chlorothalonil at 7-day intervals and sulfur at 10 to 14-day intervals. 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. Copper fungicides 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. Reflective plastic mulch may reduce disease by disorienting aphids and thus preventing them from feeding on the bean crop. Control weeds in and near the garden, which may bring aphids into the garden.
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. When the disease is first noticed, sprays or dusts of sulfur are recommended for use on snap and green beans, as well as on Southern peas. Sulfur gives good control of powdery mildew. Apply at 10 to 14-day intervals. Do not use sulfur on young plants, and avoid use on plants if temperatures are over 90 ºF. Apply chemicals according to directions on the label.
Cercospora Leaf Spot
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 for this disease in the home garden. Chlorothalonil sprays give very good control, and sulfur sprays give fair control of Cercospora leaf spot. 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.
Watery Soft Rot
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.
Table 2. Fungicides to Control Bean & Southern Pea Diseases.
|Fungicides||Examples of Brands & Products|
|Chlorothalonil||Bonide Fungonil Concentrate; & RTU1
Ferti-lome Broad Spectrum Landscape & Garden Fungicide Concentrate; & RTU1
GardenTech Daconil Fungicide Concentrate; & RTU1
Hi-Yield Vegetable, Flower, Fruit & Ornamental Fungicide
Ortho MAX Garden Disease Control Concentrate
Southern Ag Liquid Ornamental & Vegetable Fungicide
Tiger Brand Daconil
|Copper Fungicides||Bonide Liquid Copper Fungicide RTU1
Bonide Copper Fungicide Spray or Dust (wettable powder with copper sulfate)
Monterey Liqui-Cop Copper Fungicidal Garden Spray Concentrate (a copper ammonium complex)
Southern Ag Liquid Copper Fungicide (a copper ammonium complex)
Bonide Liquid Copper Concentrate (a copper soap)
Camelot Fungicide/ Bactericide Concentrate (a copper soap)
Concern Copper Soap Fungicide for Flowers, Fruit & Vegetables RTU1
Natural Guard Copper Soap Liquid Fungicide Concentrate; & RTU1
|Sulfur||Bonide Sulfur Plant Fungicide (dust or spray)
Ferti-lome Dusting Sulfur (also wettable for spray)
Hi-Yield Wettable Dusting Sulfur (dust or spray)
Safer Brand Garden Fungicide Concentrate
Southern Ag Wettable or Dusting Sulfur
|1RTU = Ready-to-Use (a small pre-mixed spray bottle for use in small gardens)
To protect pollinating insects, always spray as late in the evening as possible.