Introduction to Beans pests and diseases
Beans form an important food and cash crop. The beans belong to the Leguminosae family. They are considered nutritious vegetables as they have a high amount of vegetable proteins. The green tender pods are used as a vegetable and dry seeds. The beans for drying are grown till the bean seeds are large enough and pod begins to dry. The pods are shelled and then seeds are separated. The shelled dry bean has a good market.
A guide to Beans pests, diseases and control methods
The different varieties of beans cultivated in India particularly in home gardens and some commercially are as follows;
- French beans
- Cluster bean
- Broad bean
- Kidney beans
- Lima bean
- Soya bean
- Garden beans
Tips on growing Beans affected by the diseases
Many types of beans are affected by several diseases. Though, most of these bean problems can be prevented by choosing and planting disease-resistant varieties. Rotating beans at least every other year and practicing proper watering and seed spacing guidelines also help. Numerous types of fungus live in soil, which can wreak havoc on bean crops, particularly seedlings, and result in beans not growing. Roots may die and plant leaves may yellow. Plants can exhibit discoloration and poor growth. Make sure beans are planted in well-drained soil, and excessive moisture is an ideal environment for the development of fungus. Stem anthracnose is a fungus that causes bean problems in severely wet conditions.
Beans exhibit dark-colored lesions or blotches. Then, there are no remedies but with proper preventative measures, such as avoiding overhead watering, it can be avoided. Sclerotinia fungus causes pods to become soft. Plant leaves form watery spots and stem rot. Cool, moist conditions trigger this bean problem. Improve air circulation and discard bean plants. Bean rust is another common problem caused by fungus and affected plants develop rust-colored spots and leaves may yellow and drop. Plants must be removed and discarded. Avoid humid conditions and rotate plants.
Bacterial blights are common in wet environments. Halo blight attacks in cool temperatures and bean plants develop dark spots surrounded by yellowish halos. Common blight occurs in warm weather. This causes dark spots but without the halo. Both are caused by infected bean seeds and spread easily in wet conditions. Mosaic viruses are caused by herbicide use, infections, and nutrient deficiencies. Many are transmitted through pests, such as aphids, or infected bean seeds. Bean plants exhibit unusual color patches. White or gray powdery growth can signal powdery mildew, which is spread through wind and rain.
Beans pests and their control
Aphids of Beans pests
Aphids are found in large colonies on underside plant leaves and tender shoots. The nymphs and adults suck the sap. So, the affected leaves turn yellow, get wrinkled, and distorted. The insect exudes honeydew on which fungus develops, rapidly covers the plant with sooty mold that interferes with the photosynthetic activity of the plant. As a result, the growth of a plant is stunted and crop yield is affected adversely. Besides, they act as a vector for transmitting by aphids and the loss caused on this account is far more severe than by their feeding and devitalizing the plant.
Control measures – Spraying with 0.05% endosulfan, 0.02% phosphamidon, 0.03% dimethoate, methyl demeton, and thiometon control the pest effectively.
Mites of Beans pests
Nature of damage – They suck the cell sap from plant leaves. Badly attacked plant leaves show a peculiar bronzy and shiny appearance, ultimately wither and dry up.
- Spray 0.2% sulphur or 0.03% dicofol
- Sulfur dusting at the rate of 20 to 25 kg/ha also gives satisfactory control of the pest.
General recommendations on Beans plant pests
Pest problems in crops tend to vary from year to year, but good cultural practices can minimize their appearance and ensure healthy bean plants that are more able to survive insect infestations. Tilling will destroy any overwintering insects and rotate bean crops from year to year to confuse and thwart bean pests.
Plant beans in full sun in late spring, 2 weeks after the last frost. Bean seeds do not tolerate cold, soggy soil and can be stunted or fail to appear altogether. Plant bean seeds about 1 inch deep and 2 to 4 inches apart. Thin them so they stand about 12 inches apart after true leaves emerge. Water them to keep the soil evenly moist, and monitor the garden for insect pests.
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Beans diseases and their control
Anthracnose of Beans Diseases
Anthracnose disease can reduce bean quality, as well as crop yield. Losses can be severe during cool, rainy weather and bean pods with black, sunken lesions or reddish-brown blotches most likely have anthracnose, a fungal disease caused by Colletotrichum lindemuthianum. Black, sunken lesions ½ inch in diameter develop on stems, pods, and seedling leaves but are most prominent on pods. Salmon colored ooze on lesions and the veins on lower leaf surfaces turn black. On lima beans, symptoms are sooty- appearing spots on plant leaves and pods. Anthracnose develops mainly during the spring and fall when the weather is cool and wet, and not during our hot, dry summers. Lima beans are mainly susceptible.
Management – Prevent this Anthracnose disease by using the certified disease-free seed for planting and removing all plant debris after harvest. Anthracnose can survive in the soil for 2 years on plant debris or be brought to the garden on infected seeds. Do not plant bean seeds in an area that had the disease for 2 to 3 years. Avoid overhead watering and avoid splashing soil onto the bean plants when watering. Fungicide sprays of fixed copper are the recommended chemical that can be used on lima beans for anthracnose control.
Bean rust is a disease of bean leaves that causes rust-colored spots to form on the lower leaf surfaces. Severely infected plant leaves turn yellow, wilt, and then drop off of the plant. Stems and pods may be infected. This disease is mainly caused by the fungus Uromyces appendiculate and it affects most types of beans under humid conditions.
Management – The fungus survives the winter in the soil, and even on poles used the previous year. In gardens where rust has been severe, crop rotation is very important. As plants begin to bloom, sulfur or chlorothalonil can be sprayed weekly on snap beans and green beans only. Do not apply chlorothalonil to lima beans. Wait 7 days between spraying and harvest when using chlorothalonil on beans, and 14 days on Southern peas. Apply chemicals according to directions on the label.
Symptoms – Mosaic viruses in which the plant leaves show sharply defined patches of unusual coloration may occur in beans. The causal agents of these symptoms can be a nutrient imbalance or herbicide injury or result from infection by one of several viruses. Like other viruses, bean common mosaic virus interferes with genetic signaling within the bean plant. Leaves that are distorted by the virus cannot function normally, so bean plants stop gaining size and may produce dense clusters of infertile flowers.
Management – There are no recommended chemical controls for these disease problems. Many of these viruses are transmitted by aphids and are transmitted through seed. For this reason, it is unwise to save bean seeds from year to year.
Do not save seeds from bean plants that show symptoms of viral infection, because the virus can be carried within the seed. Many varieties are resistant to common mosaic virus; resistant varieties can show slight symptoms, and then outgrow the problem. Measures that reduce aphid populations will cut the risk of this and viral diseases in the garden.
Bean Powdery Mildew of Beans Diseases
Damage – Powdery mildew fungi clog up leaf pores and block light to photosynthetic cells, so the bean plants are weakened in their ability to use light as an energy source. New growth stops, old leaves fall off, and the bean plants struggle to stay alive.
Preventing Problems – Do not over-fertilize beans, and which can invite problems with this disease. Thin bean plants to proper spacing so each leaf gets good exposure to sun and fresh air. Plant fast-growing bush snap beans 2 or 3 times, three weeks apart, and pull up old plants as soon as production slows. Compost old bean plants and fallen bean leaves. Use resistant plant varieties in areas where beans have persistent problems with powdery mildew.
Bean Root Rot
Damage – When you pull up an infected plant, it will have a skimpy root system with most small roots missing. A dark area of decay can be present on the main stem near the soil line.
Preventing Problems – Plant beans in soil that have been thoroughly cultivated, do not follow potatoes with beans. Thin as needed to grow bean plants at proper spacing, because crowded conditions can contribute to the development of root rot diseases. You will lose fewer seedlings to bean root rot diseases if you wait until the soil is warm to plant beans.
Bean White Mold
Damage – As pod tissues decline from this disease, and the beans become inedible. Plants can continue to grow normally. The beans inside pods rot from this disease.
Preventing Problems – Make sure bean plants get good air circulation and plenty of suns and keep weeds controlled to promote prompt drying after rains. Use mulch to keep pods from coming into direct contact with soil and avoid using sprinklers or other overhead irrigation methods after bean pods have formed. Plant soup beans for drying then they mature before seasonal rains begin.
Bacterial diseases of Beans
- Brown spots, common blight, and halo blight are very important bacterial diseases of beans.
- These diseases attack plant leaves and pods and are favored by periods of wet weather.
- The use of certified, disease-free seed varieties is an effective means of control.
Bacterial brown spot
Symptoms of brown spots initially appear as small, circular, brown spots on the leaves, surrounded by a narrow yellow halo. The spots sometimes fall out, giving the leaf a “shot-hole” appearance. Water-soaking and bacterial ooze are not seen with this disease. Small, dark brown spots can develop on pods, and early pod infections can result in the development of malformed pods.
Management strategies for bacterial brown spot consist of crop rotation, the application of copper-based bactericides, and the use of resistant varieties. A 2 to 3-year crop rotation away from susceptible hosts is recommended in some areas, but rotation may not be effective in areas where the bacterium is prevalent. Sanitation practices for field equipment and avoiding working in fields when bean plants are wet will help limit the spread of the disease. The application of copper-based bactericides can help slow the spread of the disease, but the effectiveness of such applications has been inconsistent. The use of resistant varieties is the best process to control bacterial brown spot.
The common blight of Beans Diseases
The initial symptoms of common blight are water-soaked spots on the plant leaves. As they develop, spots become necrotic, light brown, irregular-shaped lesions with distinct, bright yellow margins. Lesions can enlarge and coalesce to cause blighting of the plant leaves, leading to defoliation. Water-soaked areas can form on the pods and develop into reddish-brown spots. Pod infection can result in infection of the bean seed.
The use of disease-free seed is very important for the control of common blight. Crop rotations of 2 to 3 years can lower inoculums levels. Sanitation practices for field equipment, avoiding working in fields when bean plants are wet, and the application of copper-based bactericides can help slow the spread of common blight. Though copper applications will not eradicate the pathogen from infested fields, and continued wet conditions will result in the spread of the disease, even when copper-based bactericides have been applied. Resistance to common blight is obtainable in some varieties.
Halo blight develops as small, angular, water-soaked spots on the undersides of leaves. The spots become necrotic and reddish-brown color, surrounded by greenish-yellow halos that vary greatly in size. At temperature levels above 80°F, the halos can be small or completely absent. The infection of the pods results in water-soaked spots that can ooze bacteria.
Because the pathogen is seed-borne, the use of certified, disease-free seed is very important for managing halo blight. As with the other bacterial diseases, crop rotation can reduce inoculums surviving on crop debris, while copper applications and field sanitation practices, and including the washing of equipment that has been used in infested fields and avoiding entering fields when plants are wet, will help slow the plant-to-plant spread of this disease.
Commonly asked questions about Beans cultivation, pests, and diseases
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What is killing my green bean plants?
Spray aphids, spider mites or leafhoppers off green bean foliage and stems with a strong jet of water from the garden hose. Spray beetles, aphids, mites, and flying insect pests with an organic soap-based spray if other control methods don’t work; there is a risk of repelling and killing beneficial insects.
What is the best fertilizer for beans?
A light feeding of compost is normally all bean plants need for adequate potassium. For infertile soils, use about 5-10-10 fertilizer or add 10 pounds of ground granite or 10 pounds of greensand per 100 square feet.
Why are my beans turning brown?
When too closely spaced, there is excess competition for nutrients, sun, and water, leading to stressed plants as of the poor growing conditions. If the situation becomes too severe, the plant leaves can begin to yellow and eventually turn brown.
Do beans need manure?
Manure has been shown to give all the substances that beans need to grow, and it can be used exclusively without the need for chemical fertilizers. Manure improves the soil’s drainage capacity, a big plus where beans are concerned, as they need lots of water to grow and produce.
What is the spacing for beans?
Plant bean seeds about 1 to 1½ inch deep, a bit deeper in loose, sandy soil. Plant bush beans about 3 to 4 inches apart; set rows 18 to 24 inches apart. Plant pole beans about 4 to 6 inches apart; set rows 30 to 36 inches apart.
Why did my beans die?
When a bacterium is to blame for yellow color leaves on beans, the first sign of a problem is water spotting or dry, brown leaf edges. This progresses to encompass the entire leaf and then causes the foliage to die and drop off. The bacteria that cause this disease live in soil or are introduced in infected bean seed.
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