Common bean (Phaseolus vulgaris L.) is the world’s most important legume for human consumption, according to Katungi et al 2010. Beans are a source of proteins which makes the Kenyan population depend highly on them. The market for beans is overwhelming, and depending on the quality and type of beans, the prices per 90kg bag of beans range between Sh7,000 and Sh12,000. The price is dynamic and influenced by seasons and varieties. Some varieties which are not grown by many farmers can fetch a higher price due to the difference in demand and supply.
Improved beans
There are numerous bean varieties. Between 2008 and 2018 around 33 new varieties were released through research organisations like Kenya Agriculture and Livestock Research Organisation (Kalro), Egerton University and Kenya Seed Company.
A bean researcher from Kalro David Karanja, says the new varieties are improved beans that perform better with the changes in climate, are resilient and contain trace nutrients like zinc, which is important for human growth and body condition.
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“How many of these new varieties are known by change agents and farmers?” Mr Karanja poses. His question indicates that there is a great need to educate farmers on the new varieties for them to adopt climate smart and resilient agriculture. Some of the 33 new bean varieties include Angaza, Faida and Nyota.
Bean consumption behavior
Bean consumption behaviour also varies from place to place. Some communities consume the leaves as vegetables, others eat green beans like in the case of French and runner beans and the most common is the dry grain. The bean left over stover/stalks is also an excellent fodder for livestock and some communities burn it to make food additives called munyu by the Luhya community.
Bean Agronomy
Farmers must start by planting good quality seed for good crop establishment. The seed sourced should have the following characteristics:
• One variety (one colour or pattern)- Farmers who grow from their own seed tend to mix different varieties through seed trading with fellow farmers. This does not work in their favour as the different varieties have different growth habits hence crop interaction is not optimised for maximum production. Avoid mixing varieties not only for beans but for other crops as well.
• Viable (ability to germinate)- This can be tested out by growing 100 seed before planting and counting those that germinate. If out of 100 only 50 germinate that seed has a germination per centage of 50 per cent. Meaning, should you decide to use it, half of your farm will not have any crop. This raises production cost as farmers are forced to practise gapping. Always go for seeds with a high germination percentage.
• Free from seed-borne diseases and pest damage. To achieve this, always buy certified seed with a stamp/sticker from Kenya Plant Health Inspectorate Service (Kephis), indicating that it is free from pests and diseases as some cannot be seen by a naked eye.
• Free from inert materials. Do not plant seeds contaminated by stones or leaves. The inert materials alter the seed weight and can introduce other contaminants.
• Not shrivelled, mouldy or cracked. Cracked seed may be missing the most important part which is the embryo critical for growth. Mouldy and shrivelled seeds are indications of fungal contamination which can cause crop failure right at the start.
• Not rotten or discoloured
Seed rate
The recommended seed rate is 40-50kg/ha, which translates to 16 to 30kg per acre. During planting, farmers are expected to observe the number of seeds per hill. Sow at least two seeds per hill. The depth of planting is four to five centimetres. Do not plant beyond five centimetres as the shoot may have trouble emerging, resulting in crop failure.
Bean spacing
Bean spacing is influenced by a number of factors like variety and type of cropping system adopted. One can be growing beans for green bean production that French beans or beans for dry grain. You can also adopt different cropping systems like mono-cropping or intercropping. When grown as the only sole crop, the spacing is 50cm by 10cm a bean. Banana intercrop has a spacing of 45cm by 20cm. Different intercrops have different spacing.
Bean fertility and crop nutrition
Before deciding on any crop nutrition activity for your bean crop, it is always advisable to do soil analysis. This is because beans have the ability to fix nitrogen in the soil hence the need to follow the write crop nutrition guidelines. During planting, use well decomposed manure and DAP. DAP helps in root formation which is key for the bean crop. Consider top dressing before the crop flowers. After flowering no activity should take place till the pods form to avoid flower fall.
Weeding
Up to 50 per cent crop losses can occur due to uncontrolled weeds. The first weeding should be done two weeks after emergence. Weed early before weeds grow big and compete with your bean crop. Second weeding should be done before flowering. After flowering do not weed but hand pull weeds as necessary to prevent flower abortion and disease attack.
Key Bean Diseases & Pests
Beans are sensitive to pests and diseases and can easily be wiped out if not properly taken care of no matter the growth stage. It is therefore recommended that you take care of the beans through all the stages. Practise weekly scouting in your bean crop to assess performance and identify any pests or disease. This helps you to identify the incidences of pests and diseases early for timely management. This is before economic injury levels are attained. Economic injury levels are levels of infestation or infection which do not make any business sense to apply any control or management methods, the crop will have been lost. Always select preventative care and measures over reactive. Early intervention will save your bean crop investment.
Anthracnose disease
Anthracnose is a fungal disease mainly spread via infected seeds. Once crop is attacked by diseases, the symptoms show on stem, leaves and pods. Control is difficult. Don’t use seed from infected plants. Use clean certified seeds.
Bean common mosaic virus
Symptoms manifest as an irregular mosaic pattern of light yellow and green or a band of dark green along the veins on an otherwise green leaf. Foliage may pucker and warp in size, often causing the leaf to roll up. Grow tolerant varieties from certified seeds. Control aphids if the variety grown is not tolerant.
Fusarium Root Rot
Fusarium causative fungus thrives best in warm temperatures. Solarisation kills off the fungus by raising temperature up to an extreme heat level where no fungus can survive. Plant tolerant varieties. Practice crop rotation (and not with Irish potatoes) and treat planting seed with a fungicide like Apron Star and Murtano.
Leaf Rust
It is caused by a fungus which attacks the leaves, stems and pods of bean plants. Rust spots have red-brown powdery substance. If not controlled in good time, excessive infection eventually leads to death of plant or plant parts, causing huge losses. Plant resistant varieties. Rotate with non-host plants like cereals.
Maintain field hygiene and if infected, spray fungicides alternating active ingredient (with sticker).
Powdery mildew
Symptoms include twisted, buckled, or distorted leaves with a whitish substance. Apply Sulphur-based fungicides as preventive rather than going curative. Start the crop on well moisture fertilised soil for crop to be strong. Do not carry out overhead irrigation. Do not grow crop under shades.
Bean Pests
Cutworm
Apply an insecticide late in the afternoon for best control. A mulch of neem leaves is useful against cutworms.
Bean Fly Control
Early planting prevents high damage which come later. Earthing /building up the soil around the plants to cover the roots at two to three weeks after emergence.
Chemical control using various systemic insecticides can be adopted.
Thrips Control
Adopt different cultural control methods like timely weeding, use of neem oil and botanical control like BotaniGard ES.
Aphids Control
Cut off and compost stems holding aphid clusters. Dusting the plants with flour constipates the pests. Do weed control early enough. When problem worsens chemicals can also be used.
White Fly Control
Remove weeds which hide the pests, maintain field hygiene after weeding and use of chemicals.
Pests at Bean Podding stage
Pod Borers
Most of the pod borers are damaging at caterpillar stage, like bollworm larva, Heliothis larva. Always destroy plant debris of previous crop by either using it in a compost pit or as animal feed. This ensure that the eggs laid there will not go on to the next growth cycle. Use plant-derived products, such as neem, derris, pyrethrum and chilli (with the addition of soap).
Sucking Insects
Plant sucking bugs occur from vegetative to early podding stage. The pests can be controlled by planting repellent plants such as parsley “dhania” and onions within bean plants.
Synthetic pyrethroids are effective, but will also kill natural enemies. Use plant-derived products like in pod borers.
When using chemicals, do not repeatedly use one type of insecticide to avoid resistance. Do NOT mix insecticides and foliar fertilisers in one spray tank.
[The writer is FarmKenya Initiative project leader. BSc Agriculture, Egerton, MSc AICM, UoN]
