French beans (Phaseolus vulgaris) belong to the Fabaceae family and are bred and cultivated for their pods and seeds. Although the crop has a low consumption rate in the country, it is one of the dominating crops in the export market.
In Kenya, they are grown mostly in warm-wet regions like Nakuru, some parts of Kajiado, Thika, Murang’a, Machakos, Uasin Gishu, Western Kenya, Kisumu, Kirinyaga, Nyeri and Naivasha.
With irrigation, French beans can be grown throughout the year.
Health benefits and nutritional value of French beans
- Contain little amounts of sodium, saturated fats and cholesterol making them the best natural aid for weight loss.
- Rich in folates which prevent the foetus from neural-tube defects especially when eaten during pregnancy.
- Contain phosphorous, calcium, copper, potassium, magnesium, protein, fat, starch and omega 3 fatty acids which are essential to body health
- Rich source of, vitamins A, B, D and K.
- Rich in dietary fibre which helps in regulating fats in the body.
- Contain flavonoids and antioxidants which nullify the attack of harmful free radicals in the body thus preventing aging.
ECOLOGICAL REQUIREMENTS
Soil- the crop thrives in well drained soils which are rich in organic matter and with a slightly acidic to alkaline PH of 6.5-7.5.
Temperature- the optimum growing temperature for the crop ranges from 20-25°C but it can survive in temperatures ranging between 14-32oC depending on the variety. Extremely high temperatures result to poor flower development and pod set.
Altitude- an optimum altitude range of between 1000 – 2100M asl is suitable for the crop. However, French beans mature faster in warmer areas.
Rainfall- For rain fed farming, well distributed annual rainfall of between 900-1200mm is suitable. Irrigation should be done if rainfall is inadequate. Too much rain or long dry spells are not favourable and lower yields. Excessive rainfall during flowering causes flower abortion and increased disease incidences.
Seed selection
There are several varieties of French bean which have different colors, ranging from green, yellow and purple.
The commonly grown varieties in Kenya include Samantha, Boston, Serengeti, Amy, Belcampo, Julia, Paulista, Rexas, Lomami, Hawaii, Morgan, Pekera, Picasso, Buffalo, Tokai, Teresa, Gloria, Cupvert, Seagull and Espadia, among others.
Seed rate
For an acre piece of land, 25-30kg of certified seeds are required, depending on the variety.
Spacing
This depends on the variety, water availability and soil fertility, among other factors. However, for single rows, a spacing of 30x15cm (one seed per hole) or double rows of 60x30cm is recommended. For easy management of the crop, it is advisable to plant in blocks of four single rows which are separated by a 50cm path.
LAND PREPARATION & PLANTING
Propagation of French beans is by seeds which are directly sown into the field.
Land preparation should be done early enough in order to allow for weeds to dry and decompose before planting.
Procedure
- Spray weeds with CATAPULT® 480SL 200ml/20L, which controls broadleaf and grass weeds.
- Plough land and make it level with a fine tilth.
- Mix soil with manure and DAP. For efficient and improved nutrient uptake as well as stabilizing soil pH, mix 1kg HUMIPOWER® with 50kg DAP and /or 1 ton of manure.
- Place the seeds at a spacing of 60x20cm (2seeds per hill) or 30x15cm (1seed per hill), at a depth of 1-2 inches.
- Cover seeds with loose soil.
Tips!
- Use certified seeds from reputable seed suppliers.
- Planting should be done at the onset of the rains if production is rain fed.
- Seeds soaked in OPTIMIZER® 20ml/1L overnight prior to planting germinate uniformly and faster.
- Germination occurs in 7-14 days.
FIELD OPERATIONS
Irrigation
Moisture availability affects uniformity, yield and quality of the produce and therefore watering is essential in cases where rainfall is inadequate. It is also advisable to grow the crop on ridges and use furrow irrigation in heavy clays because French beans are very sensitive to water logging. Lack of water during flowering and pod formation causes flower abortion and curved pods leading to reduced yields.
Weeding
Weeds infestation significantly lowers the production potential of the crop as they compete with crop for growth factors and harbor diseases and pests, and therefore, proper weed management is very crucial. Apply HOTLINE® 450SC at a rate of 50ml/20L, which is a pre-emergent selective herbicide controlling both broadleaf and grass weeds. At flowering, weeding should not be done in order to prevent disturbances to the crop which would cause shedding off of flowers.
Support
Climbing French bean varieties which grow to about 6feet high should to be supported, which can be done using trellises or poles.
Crop rotation
This should be done with crops that do not belong to the Fabaceae family. It helps in weed control, pests and disease management, reduction of soil erosion, and rejuvenation of soil organic matter.
Fertilizer application
To achieve optimum yields, timely application of basal and foliar fertilizers is essential. Manure should be added especially to soils with little or no organic matter.
At planting
Apply 100Kg of DAP per acre and thoroughly mix it with the soil before planting. DAP is preferred because it contains considerably higher levels of phosphorus which helps the crop with root development. Other phosphatic fertilizers like TSP can be used.
A week after germination, the young plants should be sprayed with LAVENDER SUPER STARTER® 20ml/20L or GOLDCHANCE SUPER START® 50g/20L which promote early crop establishment besides other benefits.
Topdressing
Apply 50kg CAN per acre at the first 3-leaf stage, and 50kg per acre when the crop begins to flower. CAN fixes nitrogen in the soil which increases the green color of the leaves, responsible to make food for the plant. Other nitrogenous fertilizers like urea can also be used.
Spray the crop with GOLDCHANCE SUPER GROWTH® 50g/20L or LAVENDER SUPER GROWTH & VEGETATIVE® 20ml/20L which provide essential Nitrogen among other nutrient elements.
When the crop begins flowering and setting pods, spray it with GOLDCHANCE SUPER FLOWERS & FRUITS® 50g/20L or DIMIPHITE® 20ml/20L or GOLDCHANCE MULTISUPER K® 50g/20L or LAVENDER SUPER FLOWERS & FRUITS® 20ml/20L.These are rich in nutrient elements which promote production of quality pods. Application of VITABOR GOLD® 30ml/20l also prevents flower abortion.
Tips!
- Soil analysis is important as it helps in determining the soil fertility status.
- All basal fertilizers should be mixed with HUMIPOWER® at a rate of 1kg of HUMIPOWER® into 50Kg of fertilizer.
- OPTIMIZER® is an organic biostimulant which is essential for plant growth and stress management. It can be applied at all or any growth and development phase of the crop.
- Avoid excessive use of nitrogenous fertilizers because that may promote vigorous vegetative growth at the expense of pod formation.
MAJOR PESTS & DISEASES
Pests
Bean fly; The larva tunnels into the plant stem damaging the vascular tissue, causing reduced plant vigour and petiole droop in older crops. Severe infestations can lead to death of seedlings. Crops are at a greater risk for 3-4weeks after emergence. Affected plants are yellow, stunted, and stems are cracked at the soil level.
Spray EMERALD® 200SL 10ml/20L or PRESENTO® 200SP 5g/20L or KINGCODE ELITE® 50EC 10ml/20L
Thrips; Damage is caused by the nymphs and adults which feed and puncture leaves and flower structures. Heavy infestations lead to flower and flower buds abortion while leaves fall off.
Spray ALONZE® 50EC 5ml/20L or DEFENDER® 25EC 40ml/20L or PRESENTO® 200SP 5g/20L
Aphids; These are soft bodied, green, black or brown insects which cluster on stems, leaves, and pods from where they suck plant sap suck causing stunted growth and malformation of the infested parts. As they feed, they excrete honeydew which encourages the development of sooty mold which reduces photosynthetic area.
Spray PENTAGON® 50EC 10ml/20L or PRESENTO® 200SP 5g/20L or KINGCODE ELITE® 50EC 10ml/20L
Spray JAMBO CLEAN® 100ml/20L to get rid of the sooty mold.
Red spider mites; These are tiny reddish yellow pests found on the undersides of the leaves. Their feeding leads to formation of yellow stipples on leaf surfaces and webs are seen on the undersides of the leaves in cases of heavy infestations.
Spray ALONZE® 50EC 5ml/20L or BAZOOKA® 18EC 10ml/20L or DEFENDER® 25EC 40ml/20L
Whiteflies; These are white insects which suck plant sap causing the infested leaves to curl, become distorted and eventually drop. They secrete honeydew as they feed which facilitates the development of sooty mold on the leaves affecting photosynthesis.
Spray TAURUS® 500SP 10g/20L or PRESENTO® 200SP 5g/20L or EMERALD® 200SL 10ml/20L
Spray JAMBO CLEAN® 100ml/20L to clean the sooty mold.
African bollworm; It bores holes on pods and feeds with its head inside the pod and the rest of the body outside and this reduces their quality. It also feeds on leaves and flowers.
Spray KINGCODE ELITE® 50EC 10ml/20L or PENTAGON® 50EC 10ml/20L or PRESENTO® 200SP 5g/20L
Cutworms; These are brown to black caterpillars usually found in the soil, which cut the stem of younger plants below or above the soil level. They are active at night and hide during the day.
Drench soil with PENTAGON® 50EC 20ml/20L or LOYALTY® 700WP 10g/20L
Diseases
Rust; Infection leads to formation of slightly raised reddish brown pustules on leaves, pods and stems and severe infections may lead to death of the crop.
Spray MILESTONE® 250SC 10ml/20L or DUCASSE® 250EW 20ml/20L or DOMAIN® 250EC 10ml/20L
Downy mildew; Disease development starts on the underside of the leaf which causes the formation of whitish or grey mass of fungal growth while the upper side of the leaf turns yellow and the pods develop whitish patches.
Spray TOWER® 720WP 50g/20L or MILESTONE® 250SC 10ml/20L or KATERINA® 720SC 40ml/20L
Anthracnose; Disease development leads to formation of brown to black sunken lesions on pods and stems while the leaves develop black spots which interferes with the rate of photosynthesis.
Spray DUCASSE® 250EW 20ml/20L or DOMAIN® 250EC 10ml/20L or JUPITER® 125SC 15ml/20L
Bacterial blight; Disease symptoms begin as small brown blotches on the leaves which enlarge as infection progresses eventually causing leaf fall and subsequent death of the plant.
Spray GREENCOP® 500WP 50g/20L, a copper-based products which suppress the activity of the pathogen.
Fusarium wilt; Crop infected with this disease show sudden yellowing of leaves which eventually fall off and the vascular tissues are discoloured which cause death of the plant after sometime.
Drench soil with GREENCOP® 500WP 100g/20L and spray PYRAMID® 700WP 50g/20L
Damping off; It is a soil borne disease which causes the infected seeds not to germinate while seedlings rot and eventually die. White cottony growth is seen on the roots of the infected young plants.
Drench soil PYRAMID® 700WP 100g/20L and spray DOMAIN® 250EC 10ml/20L
Angular Leaf spots; Diseased leaves, stalks, and pods develop angular brownish spots with purple edges and grey to brown centers. Initially these spots are water soaked. Severe case of infection cause premature leaf fall.
Spray DOMAIN® 250EC 10ml/20L or DUCASSE® 250EW 20ml/20L or CHARIOT® 500SC 20ml/20L or MILESTONE® 250SC 10ml/20L
Powderly mildew; White powdery growth of the pathogen, which later turn black as infection advances, form on the stems, leaves, flowers, and pods. In severe cases leaves become chlorotic and drop off.
Spray DOMAIN® 250EC 10ml/20L or CHARIOT® 500SC 20ml/20L or JUPITER® 125SC 15ml/20L
Bean Common Mosaic (BCM); This is a viral disease which is majorly transmitted by aphids. Infection causes formation of mosaics, leaf curling and rolling, and general stunted growth of the crop.
Control of aphid vectors using PENTAGON® 50EC 10ml/20L or PRESENTO® 200SP 5g/20L or KINGCODE ELITE® 50EC 10ml/20L
Tips!
- Whenever doing foliar sprays, mix the chemical with INTEGRA 3ml/20L, which is a sticker, spreader and penetrant that increases the efficacy of the product.
- Use CADILAC® 800WP 50g/20L, which is a preventative fungicide against diseases including downy mildew, anthracnose and leaf spots.
HARVESTING & POST-HARVEST PROCESSES
Harvesting
It begins 6 to 8 weeks after planting depending on the variety and ecological conditions.
Harvesting is best done in the morning but not when the crop is too wet and is achieved through carefully picking the pods off the plant with the stalks, and not pulling. This should be done at regular intervals depending on the market specifications, for instance, twice a week for the fine French beans and three times a week for the extra fine beans, and can continue for around a month.
Harvesting the beans while young encourages more production, and the beans are tasty.
Yield
An acre can produce 4 to 6 tonnes of French beans.
Handling
Care should be taken in order to conserve the quality of the produce. For instance, the harvested beans should not be left in direct sun, and the harvest boxes should not be overfilled.
Sorting and Grading
Sorting is done in order to get rid of broken, twisted and perforated pods as well as plant debris while grading should be done according to size of the produce.
Packing
Operations involved in packing result in boxes of produce that must be in conformity with the European Union quality standard for French beans (standard EC 912/2001) and each box packed for the export market must display the product characteristics, i.e., name of producer/exporter, size, category, origin, etc.
Storage
Soon after packing, the produce should be kept in a cold room. At 4oC, and a relative humidity of about 80%, French beans can store for a week.
Market
The major outlet for French beans is the European Union market, and the export market in Kenya falls into two major seasons, i.e. high demand season ( September to March, where major supply is mainly from irrigation) and low demand season (June to September, during the long rains when supply is too high, thus lower prices.
