Good bean production starts with the right seeds, which must be certified for best harvest. Below find a summary on managing the crop.

Fertiliser requirements and application:

At planting, apply 200kg DAP/ha. The fertiliser should be applied in the planting hole or furrow and mixed thoroughly with the soil before placing the seed. Apply 100kg CAN/ha when top dressing initially at the first trifoliate leaf stage and a gain at the onset of flowering.

Application of foliar feed (eg Bayfolan or Rapid–Grow) at fortnight intervals from the fourth week post–planting to mid–poding phase also promotes higher yields.

Use of farmyard manure is recommended especially where soils are low in organic matter. It should be applied in planting furrows or holes and mixed well with soil before planting at a rate of 10 tonnes/ha.

Weed control:

Timely weeding is absolutely essential. The first weeding should be done 2–3 weeks after emergence, followed by a second weeding 2-3 weeks later.

Care should be taken to avoid damaging the shallow roots especially during the first weeding. Also, the crop should not be weeded at flowering time and when the field is wet to avoid flower shedding, spread of diseases and soil compaction.

Use of herbicides may be economically feasible for the commercial bean growers. Herbicides that can be used in bean production include, Lasso 4 EC (Alachor), Stomp (Pendimethalin) and Basagran (Bentazon).

Irrigation

Regular water supply is essential as moisture affects yields. Water stress during flowering reduces yields.

It is advisable to grow beans on ridges and use furrow irrigation in heavy soils since beans are very sensitive to water logging.

It is recommended to apply 35mm of water per week at planting to 10 days post emergence and 50mm/week thereafter to flowering stage.

Diseases

Rust: It is caused by the fungus Uromyces appendiculatus and is a serious threat to beans. It is favoured by high humidity conditions.

Characterised by presence of raised, small, white spots on the lower leaf surface, which turns red to dark brown after a few days.

Control: Use crop rotation, tolerant cultivars, chemical sprays such as Baycor, Anil and Alto every two weeks before flowering and Dithane M45 during flowering

Angular Leaf Spot: Is a fungal disease caused by Phaeoisariopsis griseola. Characterised by necrotic and well defined lesions with typical angular shape.

The lesions may then increase in size, coalesce and cause partial necrosis and yellowing of leaves. On primary leaves, lesions are usually round, larger than those found on trifoliate leaves and may develop concentric rings.

Control: Use healthy certified seeds, seed treatment using fernasan, spraying the crop with Benomyl, Baycor , Kocide 101, Dithane M45.

Root rots: Is fungal, caused by Fusarium spp, Rhizoctonia spp, Sclerotium spp etc. Affected plants show yellowing and drying of stem at soil level.

Stunting may also occur. Seedling establishment is poor, uneven growth, chlorosis and premature defoliation of severely infected plants.

Control: Seed dressing with Fernasen– D, Drenching of plants at vegetative stage with Benomyl, Brassicol or Bavistin.

Bacterial Blights: Caused by Pseudomonas phaseolicolla and Xanthomonas phaseoli. It is a serious disease in Kenya especially in cool and wet areas.

The disease is spread through splashing from exuding lesions and plant debris. Affected plants show halos on the leaves, drying of leaf margins, yellowing and water soaked pods.

Control: Use certified seeds, rouging and destruction of infected plants. For chemical sprays, use copper fungicides such as Kocide 101.

Anthracnose: Fungal disease caused by Colletotrichum lindemuthianum. The fungus is seed–borne and affects all aerial plant parts and is spread by rain splash, wind and mechanical contact and occurs in cool, damp weather.

The disease is characterised by the appearance of sunken, brown spots with black edges on pods, while on leaves, there are angular brown spots and oblong stripes on stems.

Control: Use of certified seeds, field sanitation, crop rotation, resistant varieties and foliar sprays of Benomyl, Mancoze and Propineb help curb the disease.

Bean Common Mosaic Virus (BCMV): Symptoms of the disease vary with variety, stage of growth and environmental factors.

The disease is seed–borne and transmitted by aphids. The symptoms include mosaic (mottling, curling and stunting of leaves), systemic necrosis and local malformations. The leaves may roll; become malformed and general stunting of the plant.

The plant produces excessive number of lateral shoots.

Control: Use of certified seeds, resistant cultivars, rouging of infected plants and control aphids.

Insect pests
Root knot nematodes (Meloidogyne spp): They attack roots causing lesions, root galls or swellings, plant stunting and wilting of severely infected plants.

The lesions also serve as entry points for bacteria and fungi. Affected plants are dwarfed and have distorted leaves.

Control: Crop rotation, weed control to remove plants that also hosts the nematodes, fallow infested fields and soil fumigation with Nemacur.

Bean Fly: (Ophiomyia spp; Phorbia ssp): The adult is a small two-winged inset which can be seen resting on leaves where it lays the eggs.

The damage is caused by the larvae that mine the stem and feed on the cotyledons of seedlings before or after emergence.

Affected plants are yellow, stunted, and stems are cracked at the soil level.

Control: Seed treatment with Imidacloprid, chemical sprays with Karate and soil treatment with Triazophos.

Bean thrips (Megalothrips spp): Damage is caused by nymphs and adults which feed and puncture flower structures and young pods.

Control: Before flowering, foliar spray using Diazinon starting from two leaf stage; during flowering, with Karate, Decis or ambush CY.

Other insect pests include: Aphis (Aphis fabae), Red Spider Mites (Tetranychus spp), cutworms, beetles and caterpillars.

Harvesting

For dry seed bean, the pods should be left on the plants until when about 75 per cent dry. They can then be harvested and dried to about 12 per cent moisture content before storage.

Carol Mutua,
Department of Crops, Horticulture and Soils, Egerton University.
BY: Seeds of Seeds of Gold

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