FRENCH BEANS (PHASEOLUS VULGARIS L)
Introduction
French beans are also referred to as green beans or snap beans. French beans are the immature green pods of phaseolus vulgaris and are a major export crop in Kenya.
It is grown by both large and smallholder farmers. Due to labour requirements of the crop, it is recommended to be grown on a small scale requirements of the crop, it is recommended to be grown on a small scale and possibly, with staggered planting. It is grown both for fresh consumption and processing, mainly canning and freezing.
Climatic requirements
The optimum temperature range for growing French beans is 20-25°C, but have been grown in temperatures ranging between 14-32°. Extreme temperatures result to poor flower development and poor pod set. The crop can be grown between 1,000-2,100 m altitude. However, French beans mature faster in warmer areas. Rain fed cultivation is possible in areas with well distributed, medium to high annual rainfall (900-1,200mm p.a) but to maintain a continuous production especially during the off-season, irrigation is very essential. Up to 50mm of water per week is required. This could be applied through furrow or overhead irrigation. French beans grows but on well drained, loams to heavy clay soils high in organic matter contents and a slightly .acidic to slightly alkaline acidic to slightly alkaline reaction (PH 6.5-7.5) but can tolerate pH 4.5 to 5.5.
Varieties
There are various varieties grown mainly for the export market although local consumption of French beans is gradually being adopted. The varieties Espada, maasai, Morgan, Amy, Coby, Samantha, Paulista, Nerina, Bobby beans such as groffy and skill.
Monel
This is the main variety which has been grown in Kenya for a long time but others have currently been introduced on the market depending on market preference. It is a high yielding variety with a long picking duration. The pods are grayish-green in colour, straight, long, round in cross section and fleshy. String and seed development is slow such that pods harvested too late to qualify as extra fine beans can still be marketed as fine grade beans. Flowers are purple and the seeds are black. The variety is grown mainly for fresh export market and to a lesser extent, canning.
Seed Acquisition and Preparation
Certified seed available from recognized seed agents (e.g. Kenya Seed Company) is recommended for planting. Use of seed from other sources is discouraged, but should such a case arise, seed production crop should be disease free. Seed selection must be thorough. All wrinkld or otherwise damaged seed should be discouraged. Before planting the seed should be dressed with Fernasa-D (combination of Lindane and Thiiram) rate: 3g (2 flat teaspoons per kg. of seed.
Propagation
With irrigation, French beans can be grown all year round but the main export season is from October to May. Planting should be scheduled at 2-3 weeks intervals (in convenient sized plots) to maintain continuous production and ensure proper management. French beans are sown directly into the seed bed. The land should be ploughed and harrowed properly just before planting. Planting should be scheduled so that most of the crop is ready between October to mid December and from mid-January to end of May. In warm areas, beans take 45 to 50 days from planting to first picking, hence, plant from mid-August to mid-October, then plant again early in Cecember. Single rows 30x15cm (1 seed per hole) or double rows 60x30x10cm is used. It is advisable to plant in blocks of four single rows separated by a path of about 50cm for ease of management practices. The planting calendar fro French beans is shown as annex 1-18
Seed Rate
50-60 kg of seed per hectare
Spacing
60 x 30 cm kg/ha
Fertilizer
At planting apply 200 kg D.A.P/ha. The fertilizer should be applied in the planting furrow and mixed thoroughly with the soil before placing the seed. Apply 100kg C.A.N/ha as a top dressing initially at the first trifoliate (three leaves) leaf stage and again at the onset of flowering. Application of foliar feed (e.g. Bayfolan or Rapid-grow) at fortnightly intervals from the forth week post-planting to mid-podding phase also promotes higher yields.
Manure
Use of Farm Yard Manure (FMY) is recommended especially where soiled are low in organic matter. It should be applied in planting furrow and worked into soil before planting at the of 10 tons/ha.
Weed control
Timely and thorough 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 crops 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 French beans grower. The following pre-emergence herbicides can be used.
- Lasso 4 EC (Alachlor) – 3 Litres in 400 litres of water per hectare
- Stomp (Pendimethalin) – 5 Litres in 400 litres of water per hectare
- Basagran (Bentazon) – Can be applied post-emergent at 2.5-3
Litres per hectare for control on broad
Leaved weeds.
Water
A regular water supply is essential as moisture affects yields, uniformity and quality. Water stress during flowering reduces yields. It is advisable to grow the beans on ridges and use furrow irrigation in heavy clays since beans are very sensitive to water logging. It is recommended to apply 35 mm/week at planting to 10 days post emergence and 50mm/week thereafter to flowering stage.
Diseases and Pests
Disease Symptoms Control
Rust the disease is caused by the fungus – Crop rotation and avoid
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