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FRENCH BEANS

Introduction

French beans are the immature green pods of phaseolus vulgaris grown mainly for export in Kenya. However, local consumption of French Beans is growing gradually. Both large and smallholder farmers grow French beans. Due to high labour requirements it is recommended that it is grown on a small scale, possibly with staggered planting.  It is grown both for fresh consumption and processing. Canning and freezing are the main processing done on French Beans. The peak export market demand is between October and May. They take 45 to 50 days to mature.

The information covered here include:

  1. Ecological Requirements.
  2. Varieties.
  3. Propagation
  4. Weed control
  5. Diseases
  6. Pests.
  7. Harvesting & Post Harvest
  8. Marketing & gross margins

Varieties

The main varieties grown in Kenya are: Monei, Amy, Samantha, Teresa, Julia, Vernando, Bronco, Coby, Espadia, Bakara, Claudia, Tokai, Pekera, Super Monel, Morgan, Paulista, Cupvert, Gloria, Tonivert, Rexas. The market requires freshy, straight, long, rounded in cross-section beans

Ecological Requirements

  • The optimum growing temperature range from 20-25°C. Beans have been grown in temperatures ranging between 14-32°C. Extreme temperatures result to poor flower development and poor pod set.
  • The optimum altitude range between 1,000 – 2,100m a.s.l. French beans mature faster in warmer areas.
  • For rain fed cultivation, well distributed medium to high rainfall (i.e. 900-1,200mm  p.a.) is required
  • Well drained loams to heavy clay soils, high in organic matter contents.
  • PH 6.5-7.5 but plants can tolerate up to pH 4.5
  • Crop rotations helps to control weeds, discourages diseases, protect soil from erosion, reduce insect populations, and rejuvenate soil organic matter a valuable source of nitrogen. Grass/maize- legumes recommended as it accumulates much organic matter. Should not be grown more than once, or twice at most on the same land without other crops being grown in rotation.
  • Seed rate: partly determined by variety but 30kg per acre planting rate of 1 kg per 100 ft of 36-inch row will result in seed  spacing of about 3 inches. Beans rows should be on the contours or at least parallel to the slope to reduce soil erosion.

Seed Acquisition and Treatment

Use certified seeds from reputable seed agents. Normally the produce buyers supply seeds to their contracted farmers. Should seeds come from other sources they should be disease free and well sort.    Before planting, the seed should be dressed with Fernasa-D (combination of Lindane and Thiiram) at the rate of: 3g (i.e. 2 flat teaspoons) per kg. of seed.

Manure Application

Application of 10 tons Farm Yard Manure per hectare is recommended, especially where soils are low in organic matter content.  Manure should be applied in planting furrows and worked into soil before planting.

Fertilizer Requirements

  • At planting: 200kg D.A.P per hectare should be applied during planting.  The fertilizer should be applied in the planting furrow and mixed thoroughly with the soil before placing the seed.
  • Top dressing: Apply 100kg C.A.N per hectare at the first ‘three leaves’ stage, and another 100kg per hectare at the onset of flowering.
  • Foliar Feed: Foliar feed such as Bayfolan or Rapid-grow, should be applied fortnightly, from the forth week after planting to the middle of podding phase.

Field Establishment

Growing Season:

Planting starts at the on set of rains. With irrigation, French beans can be grown all year round but the main export season is from October to May. Sowing should be scheduled such that most of the crop is ready between October to mid December, and from mid-January to end of May.

Planting Schedule:

To maintain continuous production, planting should be staggered at 2-3 weeks intervals in conveniently sized plots.

Spacing:

Beans should be sown in single rows of 30 by 15cm, (1 seed per hole); or double rows 60 by 30 by 10cm. It is advisable to plant in blocks of four single rows, separated by a path of about 50cm, for ease of management.

Seed Rate:

One hectare takes a total of 50-60 kg of bean seed. French beans are sown directly into a well prepared seed bed.

Picking time:

In warm areas, beans take 45 to 50 days from planting to first picking.

Irrigation

Regular water supply is essential as moisture affects yields, uniformity and quality.  It is advisable to grow the beans on ridges and use furrow irrigation in heavy clays. This is because beans are very sensitive to water logging.

  • To maintain a continuous production especially during the off-season, irrigation is essential.
  • It is recommended to apply 35 mm/week at planting to 10 days post emergence and 50mm/week thereafter to flowering stage.
  • Water could be applied through furrow or overhead irrigation.

Mulching

Mulching helps establishment under wet conditions because young bean seedlings are prone to fungal infection caused by soil splash.

Weed control

Timely and thorough weeding is absolutely essential.  The first weeding should be done 2-3 weeks after emergence. Second weeding should follow 2-3 weeks later. Care should be taken to avoid damaging the shallow roots especially during the first weeding. 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 could be economical for the commercial French beans grower.

The following pre-emergence herbicides can be used: –

  • Lasso 4 EC (Alachlor) at 3 Litres in 400 litres of water per hectare
  • Stomp (Pendimethalin) at 2.5 Litres in 400 litres of water per hectare
  • Basagran (Bentazon)     can be applied post-emergent at 2.5-3lts/ Ha for control on broad-leaved weeds.

Pests & Diseases

Root Knot Nematodes

Root-Knot (Meloidogyne ssp.), lesion(Pratylenchus spp), sting(Belonolaimus spp.), stubby-root( Trichodorus spp.) and cyst (Heterodera spp.). Root-knot is probably the most common nematode and causes the most damage.

Symptoms

These 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 with non-susceptible crops such as maize and grasses.
  • Good weed control to remove weeds which are also hosts to the Nematodes.
  • Leaving fallow infested fields during dry  weather.
  • Soil application of 5 gm/m² Mocap at planting, or 6-10 gm/m2 Ethoprophos, 2-3 times a year.

Bean Fly

(Ophiomyia spp, Phorbia spp)

Symptoms

The adult is a small 2-winged insect which can be seen resting on leaves where it lays the eggs.  The damage is caused by the larvae which mine the stem. The larvae also feed on the cotyledons of seedlings before or after emergence. Affected plants are yellow, stunted, and stems are cracked at the soil level.

Control

Spray with chemicals such as:

  • Cypermethrine at 100ml/20lt at 7 days intervals,
  • Fenvalerate at 100ml/20lts at 7 days interval.
  • Karate and decis could be applied in the stages that follow through the harvesting period, at weekly intervals.

Treat soils with chemicals such as:

  • Triazopho, at 30-60 ml/100lt, at 10-14 days intervals, or
  • Chlopyrifos at 150ml/100lts. At 7 days intervals.
  • For Triazophos and chlopyrifos, allow 21 and 7 days pre- harvest interval respectively.

Seed treatment with chemicals such as:

  • Imidacloprid at 570gm/100kg of seeds.
  • Cypermethrin at 100 ml/20L At 2 weeks intervals
  • Fenvalerate at 100ml/20lts at 7 days intervals.

Bean Thrips

(Megalothrips Spp)

Symptoms

The damage is caused by the nymphs  and adults which feed and puncture flower structures.

 Control

  • Foliar spray before crop flowering
  • Apply Karate Decis or Ambush CY during flowering

Aphids

(Aphids fabae)

Symptoms

Aphids cluster on plant stems, leaves, and bean pods. They suck plant sap and cause the plants to stunt.

Control

  • Chemical sprays as for bean fly above.

Red Spider Mites

(Tetranychus Telarius)

Symptoms

These are tiny organisms also known as red spider mites, since they are in the same group as spiders.  Their main damage is on the leaves which turn silvery and brownish in colour. Infested leaves have cobwebs on the lower leaf surface.

Control

  • Weed control to remove alternate hosts.
  • In severe infestation, burn the bean straw.
  • Spray with chemicals such as Kelthane (or Dicofol), Cabaryl, Dimethoate, Tedion (or Tetradifon 18 percent E.C). The safety period for Kalthane is 7 days, while. for the others it is 14 Days.

Cutworms, Beetles and Caterpillars

(Agrotis Spp, Astylus spp Rutelinae spp)

Symptoms

These are active at night and hide during the day. They cut stems of young plants above or below soil level. They also feed on plant foliage.

Control

Treat soil with chemicals such as:

  • Chlorpyrifos, at 150150ml/100lts, at 7 days intervals. Observe 7 days pre-harvesting interval.

Foliar spray using chemicals such as:

  • Deltamethrin, at 30-50 ml/20lts, at 7-10 days interval and 7 days pre-harvest interval.
  • Cabarl, at 50gm /20lts, at 15 to 21 days intervals and 14 days pre-harvest Interval.
  • Malathion at 30-35ml/20lts and 14 days pre-harvest interval.
  • Fenitrothion at 40 ml/20lts. (14 days intervals, 7 days pre-harvest interval).

American Ballworm

(Heliothus armigera)

Symptoms

The larvae bores holes in flower buds and young maturing pods. Pods either fails to form or don’t develop to maturity.

Control

  • Foliar sprays with Bestox, Thuricide, Desis.
  • Physical removal

Rust

Causes

The disease is caused by the fungus Uromyces appendiculatus. This is a very serious disease to French Beans and other food beans.  The development of the disease is favoured by high humidity conditions.

Symptoms

The disease is recognized by the presence of slightly raised, small white spots, on the surface of the lower leaf. The spots turn red to dark brown after a few days.

Control

  • Crop rotation
  • Use of tolerant varieties.
  • Chemical sprays such as: Baycor 30 percent EC , Bitertanol, Anvil, Alto 100  SL,  or Dithane M45 should be applied after every two weeks.

Angular Leaf Spot

Causes

This is a fungal disease caused by Phaeoisariopsis griseola.

Symptoms

Leaves, stalks, and pods have angular brown or red coloured spots with purple edges and grey to brown centres. The leaves may then fall prematurely.

Control

  • By use of healthy, certified seeds.
  • Treat Seeds using chemicals such as  fernasan-D, at 3gm per kg of seed.
  • Spray with chemicals such as benomyl (or benlate)

Root Rots

(Quintozene)

Causes

These are fungal diseases caused by the fungus Rhizoctonia spp, Pythium spp Sclerotium spp etc.

Symptoms

Affected plants show yellowing and drying of stem at soil level. Stunting may also occur.  The crop may also show poor seedling establishment, uneven growth, chlorosis and premature defoliation of severely infected plants.

Control

  • Seed dressing with a chemical such as: Fernasan-D , at 3gm per kg of seed, or Quitozene.
  • Drenching with chemicals such as: Brassicol (or Quitozene), Benomyl (or Benlate), or Bavistin, during the vegetative stage.

Bacterial Blights

Causes

The condition is caused by Pseudomonas Phaseolicola and Xanthomona phaseoli . It is a serious disease for beans in Kenya, especially in cool and wet areas. The disease is spread through splashing from exuding lesions and plant debris.

Symptoms

Plants show ring-like spots on the leaves, drying of leaf margins, yellowing and water-soaked pods.

Control

  • Use of certified seeds.
  • Roguing and destruction of affected plants.
  • Crop rotation.
  • Chemical sprays using copper-based fungicide such as: kocide 101.

Anthracnose

Causes

The disease is caused by a fungus known as Colletotrichum lindemuthiamum. The fungus is seed-borne and affects allaerial plant parts.  It is spread by rain splash, wind or mechanical contact. The disease usually occurs in cool, damp weather.

Symptoms

The disease is characterised by appearance of sunken, brown spots with black edges on pods; angular brown sports on leaves; and oblong stripes on stems.

Control

  • Use of certified seeds.
  • Field sanitation.
  • Crop rotation.
  • Use of resistant varieties.
  • Foliar sprays using chemicals such as: Benomyl, Mancozeb, propineb.

Bean common Mosaic Virus (BCMV)

Causes

The disease is seed-borne and it is transmitted by aphids.

Symptoms

The symptoms of this disease vary with variety, stage of growth, and environmental factors. They include a mosaic (i.e. mottling, Curling and stunting of leaves,) systemic Necrosis and local malformations.  The leaves may roll, malform and general stunting of the pant.  The plant produces excessive number of Lateral shoots.

Control

  • Use of certified seeds.
  • Plant resistant varieties
  • Rouging of infected plants.
  • Control of aphid vectors using insecticides.

Powderly Mildew

Causes

It is caused by a fungus known as Erysiphe spp.

Symptoms

Attacks stems, leaves, flowers, and pods which appear covered with white powdery growth which turn black latter. In severe cases the leaves turn yellow and drop off.

Control

  • Field hygiene
  • Crop rotation
  • Chemical fungicides eg. Dithane M45, Antracol, Bayleton

Downy Mildew

Causes

Caused by a fungus known as perenospora spp.

Symptoms

The underside of leaves exhibit white to greyish growth which later cover whole leaf surface.

Control

  • Field hygiene
  • Crop rotation
  • Chemical fungicides eg. Dithane M45, Antracol, Bayleton
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