Common Bean
Suggested Counties Opportunities
Agriculture could be significantly impacted due to risks associated with current climate variability and climate change. Some of these climate risks include; changes in rainfall patterns, increased temperature, and variations in the frequency and intensity of extreme weather events such as drought and floods. It is projected that the most common bean-growing areas will be under Moderate and high drought risks during March to May growing season. However, moderate risk is expected from October to December. Drought impacts bean production through accelerated soil moisture loss, reduced soil fertility through a high rate of soil organic matter decomposition, and erosion by wind resulting in bean crop failure and low productivity. High temperatures also trigger the emergence of new pests and reduce their life cycles leading to increased pest outbreaks.
Introduction
Common bean is an annual leguminous plant usually grown for its edible dry grains, fresh grains, or leaves. It’s the third most important food crop after maize and potatoes in Kenya. The grain constitutes a major source of cheap protein. It has some substantial amounts of micro-nutrients such as iron, zinc, thiamin, and folic acid. Beans are cooked by steaming the green leaves, boiling or baking the grains. The grain can also be processed into flour for making various products such as cookies, mandazi, and uji.
Common beans have a short growth cycle (about 70 days) which permits production when rainfall is unreliable. Its cultivation enriches the soil by adding nitrogen fertilizer through atmospheric nitrogen fixation. Beans are well suited to diverse environments and fit in various cropping systems. They are mainly grown in the Eastern, Nyanza, Central, Western, and Rift Valley regions of Kenya.
Major constraints of production are due to increasing moisture stress as a result of climate change, low soil fertility, and over-cultivation with little addition of soil amendments, poor cultural practices, and inadequate bean production technology transfer.
Common beans, like other crops, depend on various weather elements for their growth and survival. Weather conditions play a critical role in the development, productivity, and overall health of bean plants. Temperature and rainfall are important weather elements for the production of beans. The timing of planting, flowering, and harvesting of beans is often based on seasonal patterns of temperature and rainfall. Changes in seasonal patterns due to climate change can disrupt the synchronization between crop growth stages and weather conditions, affecting yields and crop quality. Farmers should therefore increase their understanding of climate change in order to implement activities that will help them either adapt, cope, resist, mitigate, or become more resilient to climate change uncertainties.
Climate change
Climate change refers to long-term change in climate patterns (such as rainfall and temperature) that is caused primarily by human activities that emit harmful gases into the atmosphere. These gases trap heat from the sun in the environment, leading to a gradual increase in average temperatures on the Earth. Climate change is characterized by rising temperatures, unpredictable and unreliable rainfall, and increased occurrence of extreme weather events such as droughts and heat waves. Bean production could be significantly impacted due to risks associated with current climate variability and climate change. There is a need to understand and implement adaptation options that can reduce these risks.
Climate resilient agriculture (CRA) practices
Climate resilient agriculture refers to the practice of implementing strategies, techniques, and approaches that enhance the resilience of crops and farming systems to climate-related risks and uncertainties. By adopting climate-resilient agriculture practices, farmers will increase their bean productivity, reduce the vulnerability of their agricultural systems to climate change, minimize yield losses, and maintain or improve food security and livelihoods.
Climate change risks and Impact on beans production
Climate hazards are the adverse weather events or conditions associated with climate variability and climate change which pose risks to the growth, development, and productivity of bean crops. Common climate hazards in bean production include:
Heat stress
Increased heat and heat stress will lead to risks of crop failure. The impact of heat stress on beans includes; crop stress, flower abortion, poor filling of the pod, increased crop susceptibility to pests and diseases, and reduced grain yield and quality.
Drought or prolonged dry spell
Drought and/or dry spells lead to risks of crop failure. Droughts result in flower abortion, poor seed set, reduced plant growth, the withering of bean plants, increased demand for irrigation, a high surge of pests like aphids and white flies, high incidences of common bean mosaic virus diseases, and reduced grain yield and quality.
Soil degradation
Soil degradation can lead to risks of crop failure. Growing beans on degraded soil can result in crop stress, reduced quality & yield, and increased susceptibility to pests and diseases.
Intense rainfall or floods
Flash floods/ Flooding and/or wet spells can lead to risks of crop failure
Intense rainfall can impact bean production through delayed land preparation, delayed planting, and harvesting, crop destruction, leaching of fertilizers, and high incidences of fungal diseases.
Climate Information in bean production
Common bean productivity like other crops is dependent on weather elements such as rainfall and temperature. Accurate and relevant climate information therefore should be made accessible to bean farmers and stakeholders in order to make key decisions in their farms. In Kenya, weather information from the Kenya Meteorological Department is communicated to farmers through several communication channels such as television, radio, newspaper, Ministry of Agriculture extension unit, personal contact, and SMS on mobile phones. Kenya agricultural observatory platform (KAOP) is a mobile application that is also being used to disseminate climate information to farming communities. Accurate and timely climate information is supporting bean farmers in making informed decisions regarding which crop variety to plant, planting dates, planning irrigation schedules, fertilizer application rates, and pest and disease management practices among others.
In Kenya, there are many bean varieties developed by research institutions that are available to farmers. These varieties are classified based on their area of adapted growing areas. There are some varieties that perform well in drought-prone areas while others are suitable for areas with medium to high rainfall.
Mwitemania (GLP92): Pinto
● One of the oldest drought tolerant bean variety
● The plant has indeterminate growth habit
● Flowers in 30-35 days
● Flowers are white in colour
● Matures in 70-90 days
● Grain colour is brown with beige specks
● It has medium size and elliptic in shape
● Potential yields 1200-1500 kg/ha (5-7 bags/acre)
KATX56
● The plant has determinate growth habit with an average height of 35-40cm
● Flowers in 30-35 days
● Flowers are pink in colour
● Matures within 60-65 days
● Grains are red in colour with kidney shape
● Potential yields are 1400-2000 kg/ha or 7-10 bags/acre
● Has tolerance to diseases like rust, charcoal rot, angular leaf spot and common bean mosaic virus.
KAT B9
● Has determinate growth habit plant with an average height of 35-40cm
● Flowers within 30-40 days after sowing
● Flower colour is white
● Has a uniform flowering period.
● Matures within 60-65 days
● Grain is brilliant red in colour, medium sized and circular to elliptic in shape
● Potential yield is 1400-1900 kg/ha or 7-9 bags/acre
● Tolerant to common bean mosaic virus and rust
Kat B1
● A determinate plant with an average height of 35-40cm
● Flowers are light pink in colour
● Flowers within 30-35 days
● Matures in 60-65 days
● Grain colour is greenish yellow, medium in size and circular to elliptic in shape
● Potential yield 1200-1600 kg/ha or 6-7 bags/acre
● Grains are tasty and low flatulence.
● Tolerant to diseases such as rust, common bean mosaic virus (CBMV), angular leaf spot and common bacterial blight
● Highly tolerant to heat and grows well under tree/banana shades
Kat X69
● Has determinate plant growth habit
● Flowers in 30-35 days
● Has white flowers
● Matures within 60-65 days
● The grain is red mottled in colour, medium sized and elliptic kidney shaped
● Potential yields are 1400-2000 kg/ha or 7-10 bags/acre
● It is tolerant to diseases such as rust, common bean mosaic virus (CBMV), angular leaf spot and charcoal rot.
KATRAM
● Has determinate plant growth habit
● Its drought tolerant
● Has pink flowers
● Flowers in 30-40 days
● Matures in 60-70 days
● It has red mottled grain colour with elliptic shape
● Grain yield is 1500-2000 kg/ha (6-9 bags/acre)
● Has uniform flowering and maturity
● Resistant to bean rust and Bean Common Mosaic Virus (BCMV)
Nyota
● It’s a drought tolerant variety
● Grow in cold dry highlands
● Has determinate growth plant habit
● Has pink flowers
● Flowers in 30-40 days
● Has a uniform flowering period
● Matures in 60-70 days
● The grain colour is red mottled, medium sized and elliptic shaped
● Grain yield 1400-2000 kg per ha (6-9 bags per acre)
● Has high levels of iron and zinc grain content
● It’s tolerant to diseases such as rust, common bean mosaic virus (CBMV) and Angular leaf spot.
Mwezi Moja (GLP 1004)
● Has determinate growth plant habit
● Flower is white in colour
● Flowers in 30-40 days
● Matures in 60-70 days
● Grain is violet in colour, medium in size and narrow elliptic in shape
● Potential yield is 1200-1500 kg/ha or 5-7 bags/acre
● Tolerant to bean fly
Medium and high rainfall areas varieties
The varieties in this section are suitable for medium and high rainfall areas of Western, Northern Rift and Central Kenya.
KK Rosecoco 194
● Has determinate growth habit
● Flowers are pink in colour
● Flowers in 35-40 days
● Matures in 75-80 days
● Grain colour is red mottled, medium sized with circular to elliptic grain type
● Grain yield is 1800-2000 kg per ha (8-9 bags/acre)
● Its resistant to diseases such as Pythium root rot and Fusarium root rot
KK red 16
● Indeterminate bush bean
● Flowers about 35 days
● Flower colour is pink.
● Matures within 75 days
● Grain colour is red, small sized and circular to elliptic shaped
● Potential yield is 1800-2000kg/ha or 8-9 bags/acre
● It is resistant to Pythium root rot and Fusarium root rot diseases
Canadian Wonder (GLP 24)
● Has indeterminate growth habit
● Has white flowers
● Flowers in 35-45 days
● Matures in 90-100 days
● Grain shape is an elliptic kidney with dark red colour. Potential yield is 1300-1800 kg/ha or 6-8 bags/acre
● Moderately resistant to angular leaf spot disease
Wairimu Dwarf
● Has determinate growth habit
● Flowers in 40-50 days
● Has white flower colour
● Matures in 75-84 days.
● Grain colour is red, medium in size and circular to elliptic in shape
● Potential grain yield is 1500-1750kg/ha (6-8 bags/acre)
Tasha
● Has determinate growth habit
● Has white flowers
● Flowers in 35-40 days
● Matures in 75-80 days
● Grain colour is red mottled, medium sized with elliptic grain shape
● Potential grain yield is 1800 -2000 kg per ha (8-9 bags /acre)
Chelalang
● Has determinate erect growth habit
● Has white flowers
● Flowers in 40-45 days
● Matures in 80-90 days
● The grain colour is red mottled, large sized, with elliptic circular grain shape
● Potential grain yield is 2,000-2500 kg per ha (10-12 bags /acre)
Faida
● Has indeterminate growth habit
● Has white flowers
● Flowers in 35-40 days
● Matures in 74-84 days
● The grain colour is red-mottled, large sized with elliptic kidney shape
● Potential grain yields is 1400-2000 kg per ha (7-10 bags per acre)
Angaza
● Has determinant growth habit
● Has pink flowers.
● Flowers in 40-42 days.
● Matures in 75-85 days.
● Grain colour is beige with red speckles, medium sized with rectangular elliptic grain shape,
● Potential grain yield is 6-12 bags per acre.
● Sweet grains with low flatulence levels
Choosing appropriate bean varieties that are adapted to the local climate and can withstand climate-related stresses is a key strategy in building resilience within the agricultural system.
Factors to consider when selecting varieties include:
● Agro-ecological requirements. In areas prone to water scarcity or irregular rainfall patterns, selecting bean varieties with drought tolerance is essential.
● Yield potential under prevailing conditions. By selecting high-yielding varieties, farmers can offset potential yield losses due to climate-related stresses, such as heat, drought, or pests.
● Market acceptability.Considering market acceptability when selecting bean varieties ensures that farmers are producing crops that have demand in the market. This, in turn, contributes to the economic viability of their farming enterprises, enabling them to invest in climate-resilient practices and technologies.
● Suitability of the variety in the farmers cropping system. For instance, under the cereal bean intercrop system, farmers should select bean varieties with determinate growth habit to avoid the beans climbing on the cereal intercrop.
● Tolerance to pests and diseases and drought. Resistant varieties can withstand disease pressure and minimize yield losses, reducing the need for chemical interventions.
Choosing appropriate sites for bean cultivation can help mitigate the risks associated with climate-related factors and optimize the productivity and resilience of the crop.
● Select sites that are not steeply sloping areas prone to soil erosion as it helps in preserving soil quality, reduce nutrient loss, and enhance overall crop resilience.
● Choose sites with well-drained soils that offer good water infiltration and aeration that promotes healthy root development, reduces the risk of waterlogging for optimal nutrient uptake for beans.
● Avoid sites with known pest or disease hotspots, such as areas prone to certain pests or soil-borne diseases, to reduce the risk of crop damage and yield losses.
The most important ecological factors considered for production of beans include altitude, rainfall, soil and temperature
Soil
● Beans grow on a wide range of soil types but best growth is obtained in well-drained soils with high organic matter.
● Soil analysis is important to determine the nutrition status of the soil. Farmers ought to consult extension providers on their soil type determination for bean production and in collection of soil samples for analysis. Soil sampling procedure is illustrated below.
● The optimum soil pH should be between 6.5 and 7.5.
Altitude
● Beans require altitudes of 1000 – 2000m above sea level
Rainfall
● The bean crop requires a well distributed annual rainfall of between 800-1500mm (400-500mm growing seasonal rainfall) for the rain fed production. Alternatively, irrigation could be availed if rainfall is inadequate to avoid crop failure.
● Too much rain or long dry spells are not conducive and reduces yields of bean crop
● Excessive rainfall during flowering causes flower abortion and increased disease incidences.
● Dry weather conditions are needed during harvesting, hence farmers ought to synchronize activities as required for production to maximize yield in the prevailing conditions.
Temperature
● Bean crop performs well in a warm climate with optimal temperature of 18-24 °C.
● Relative high temperatures affect flowering and pod setting processes.
● The crop is extremely sensitive to frost.
● Where temperature is greater than 30 degrees use of shade net will be essential to prevent grain yield loss.
● In areas where temperatures are below 21 °C delay of maturity and seed formation result into empty pods.
● If temperatures are low, production in greenhouse structures of plastic covers will provide a higher temperature for crop development and better yields
Seed Sources
Farmers can obtain seeds through formal or informal sources.
● Formal sources of seeds include agricultural research institutions, seed companies and registered seed stockists. The seeds from the formal system are usually certified by KEPHIS and therefore of high quality in terms of germination percentage, true to type and free from pests and diseases.
● Informal sources include seeds saved from previous season, seeds sourced from neighboring farmers and grain purchased from local markets. Seeds through informal sources need to be sorted and treated with seed dressing chemicals to improve their quality.
● Prepare the land at least two weeks from the onset of rains. This will expose them to the sun and kill the harmful soil insect’s pests and pathogens.
● Use hoe, ox plough or tractor to plough and loosen the soil to a fine tilth. Manually remove any noxious weeds like couch and nut grass after ploughing.
● Alternatively, use zero tillage land preparation by using herbicides to kill weeds and unwanted crops. This reduces soil erosion, formation of hard pan, conserves soil moisture and maintains good soil structure and health due to less disturbance of microorganisms.
● In areas with limited moisture, farmers can use chisel ploughs which have permanent prongs/tines that allow minimal overturning of soil thereby improving on water infiltration and retention.
● In areas with compacted soil, rippers can be used to break hard pans for improving soil aeration, moisture, and infiltration.
● Timing: bean seeds should be planted immediately after the onset of the first heavy downpour of about 30 mm. Farmers can take advantage of favorable weather conditions at the beginning of the growing season to establish and develop the crop before periods of extreme weather, such as droughts.
Common bean production months in Kenya in varied regions
● Planting should be done in rows to acquire the correct spacing and seed rates.
● Seed rates depend on size of seeds with the large seeded varieties requiring more seeds. One acre of land requires 16-30 kg of seed depending on seed size. 20-30 Kg of seed is required per acre for the large and medium seeded varieties such as Faida and Nyota. 16-20 Kg of seed is required for the small seeded varieties.
● Spacing: Adequate plant spacing allows each bean plant to access essential resources like sunlight, water, and nutrients more efficiently. The recommended bean spacing is 50 x 10 cm under mono-cropping system in medium and high rainfall areas. In drier areas, a lower population of 70 x 15 cm is recommended.
● Beans crop requires to be supplied with sufficient nutrients for optimum growth. Inadequate nutrients result in crop stress, reduced quality and yield and crops become susceptible to pests and diseases.
● Soil testing is recommended for proper decision on what type of soil fertility to apply.
● Apply well decomposed farmyard/ compost manure, along the planting furrows and mix with the soil at a rate of 6-8 tons per acre one week before seeds are sown. This helps in improving soil fertility, moisture holding capacity and promotes beneficial soil microorganisms.
● During planting, apply of DAP or compound fertilizer (20:20:0 or 23:23:0) at a rate of one (1) bag per acre and/ or depending on the soil analysis results.
● Foliar fertilizers which supply nutrients through leaves can be applied during vegetative, flowering and early podding stages to provide micronutrients.
● Use water saving irrigation systems such as drip irrigation that delivers water directly to the root zone thus minimizing evaporation and reducing water losses due to runoff.
Rain water harvesting:
● In dry weather conditions areas, Zai pits can be used when planting beans to prevent fast loss of soil moisture. Zai pits are shallow, wide pits that are dug to collect and retain runoff to allow infiltration into the soil. They are normally 10-15 cm deep, 15-50 cm wide and 80-100 cm apart.
Mulching
● Apply organic mulch (such as maize straw, dry grass) around bean plants. Mulching help to conserve soil moisture by reducing evaporation, improving overall water infiltration and retention capacity.
Weeds compete with the bean crop for nutrients, light and water resulting in reduced yield. Timely and thorough weeding is therefore absolutely essential.
● Timely weeding: Carry out the first weeding 2-3 weeks after emergence followed by a second weeding 3 weeks later (just before flowering). Take care to avoid damaging the shallow roots especially during the first weeding. Avoid weeding during flowering time to avoid mechanical damage of flowers.
● Clean bean seeds: Use of clean seed helps to prevent the introduction and spread of weed seeds into the fields.
● Hand weeding can be done using a jembe or a panga. During the second weeding hand pulling of the weeds can be done. Clean farm equipment before moving from one location to another.
● Mulching can be used to smother weeds. Mulches may be organic or synthetic. Organic mulches include plants by products such as wood chips, green waste, compost, leaves and grass.
● Herbicides: You can also use selective herbicides such as Bentazone about 2 weeks after crop emergence to control the weeds. Use of herbicides prevents soil disturbance, and is also cheap in terms of labour and time.
● It is important to always use protective clothing when handling chemicals.
Herbicide applied on bean plot
● Care should be taken when using fertilizers, herbicides and pesticides not to overuse them and cause pollution or eliminate non-target organisms like bees.
● Crop rotation: Crop rotation can disrupt the life cycles of weeds, reduce their population and suppress their growth. Farmers can practice crop rotation with cereals such as maize, sorghum and millet. Other crops include cabbage, kales, sweet potatoes, tomatoes and onions.
● IPDM is one of the climate resilient agricultural practices that is recommended for pest management in potato production.
● The goal of IDPM approach in bean production is to eliminate or reduce initial pests, reduce their effectiveness, delay onset of a pest attack, slow down pest spread, reduce/or eliminate use of pesticides, reduce greenhouse gas emissions and ensure health and safe diets.
● Scouting, also called crop monitoring, is a key tool in IPDM. Its objective is to detect problems before any intervention is executed or before the problems get out of control. Crop scouting must be regular; at least once a week and should be carried out in the morning hours.
The most important pests and diseases of common beans and their management practices are discussed below.
Cutworm
Symptoms
● They cut stems just below the soil base immediately after the seedlings emerge from the soil.
● A scratch of the stem base bears the presence of caterpillars; black or white depending on the species.
Control
● Scouting the fields before midday
● Seeds dressing with insecticide just before planting
● Avoid use of slurry manure; animal or plant manure not fully decomposed as this source of alternative food for cutworms
● Bait caterpillars with mixing carbaryl insecticide with molasses and incorporate in soil where seeds are planted.
Bean fly
Symptoms
● Bean fly causes swelling of bean stems around the soil base.
● Affected plants appear wilting and drooping
● Severe infestations can lead to death of seedlings in a dry environment.
● Crops are at a greater risk for 3-4 weeks after emergence.
Control
● Dress seeds with appropriate chemicals
● Uproot pest infested plants and burn to destroy habitat of the pest in the next planting season
● Rotate field plot with non leguminous crop type such as maize, sorghum and sweet potatoes.
Thrips
Symptoms
● Thrips attack plant petioles and leaves
● Leaves have tiny holes surrounded by discoloured areas
Control
● Plough and harrow before planting
● Conserve natural enemies
● Spray with insecticides such as Spinosad or other insecticides for example Endosulfan, Lufenuron & Lambda Cyhalothrin.
Aphids (Aphis fabae)
Figure: Bean plant heavily infested by aphids
● Aphids are soft bodied, green, black or brown insects which suck plant sap from leaves and shoots
Symptoms
● Aphids have piercing mouthparts used suck saps from leaves and young shoots causing leaf curling and distortion especially on the young leaves.
● Other symptoms include leaf yellowing and wilting
Control
● Practice early planting in the season and destroy volunteer crops and weeds
● Crop rotate with non-legume family crops to avoid high pest build up
● Conserve the natural enemies such as lady bird and parasitic wasps by managing foliar insecticides.
● Conduct regular scouting in the field
● Spot spray aphid infested areas only instead of the entire field.
● Under heavy infestation, spray with neem based biopesticides at recommended rate.
● Use other insecticides such as Acephate, Lambda-cyhalothrin, Chlorpyrifos and Acetamiprid based products
Pod borers
Pod borer feeding on pods
Symptoms
● Pod bugs feeds on leaf buds and bores into the young pods to eat seeds
● The caterpillar feeds on leaves, flowers, terminal buds and pods causing round holes.
● The presence of feces are evident on the surface of the infested plants
Control
● Avoid planting susceptible crops adjacent to each other.
● Deep plough the soils after harvesting to expose the pupae to predators.
● Rotate legumes with cereal crops such as maize and sorghum.
● Spray Deltamethrin and Bifenthrin based products
Pod sucking bugs
Symptoms
● The adult bugs are stout, furry and about 10 mm long and brown in colour and have a pair of elongated spines on their shoulders
● The bugs pierce the pod walls and suck the developing seeds. This leaves tiny depressions or dimples on the pod wall.
● The seed rots or shrivels and loses viability. The whole pod may shrivel
Control
● Conserve natural enemies such as the assassin bugs and ants.
● Botanical pesticides such as neem seed kernel extract to repel the adults and nymphs
● Use of pesticide sprays, such as Cypermethrin and Imidacloprid to control early instar nymphs.
● Spray in the morning when the immature stages are more exposed.
Bean Bruchid (Acanthoscelides obtectus)
Symptoms
● Bruchids lays their eggs on the surface of beans
● Eggs hatch to larvae which bore into the seeds to feed and develop leaving them perforated with holes.
● Such seeds lose viability and are unfit for planting and human consumption
Control
● Harvest early before splits appear in pods to avoid field infestation
● Dry seeds thoroughly before storage
● Tumble seeds in a sack or roll seeds in drum to clash eggs and stop new larvae from penetrating the seed
● Apply insecticides dusts to control heavy bruchids infestation.
● Ensure the grain moisture level is at 12% or below
● Use hermetic bags where care is taken to make sure live beetles are excluded at the initial storage part
Plant diseases
Bean rust on leaves
Bean rust on pods
● Conditions: The disease is favored by cool to moderate temperatures with moist conditions that result in prolonged periods of free water on the surface for more than 10 hours
Symptoms
● The symptoms include raised orange to yellow powdery pustules mainly on leaves.
● In severe cases stems and pods are affected and leaves may fall off prematurely
Control
● Plant rust-resistant varieties
● If only a few plants are infected pick off, remove and destroy all infected leaves
● Prevent unnecessary movement into the field as it will spread more the rust
● Spray fungicides with active ingredients such as Mancozeb and Chlorothalonil.
● Practice crop rotations with non-legumes for 2-3 seasons
Bean anthracnose
Pods and leaves affected by anthracnose disease
● Conditions: common in areas with frequent rainfall and cool to moderate temperatures with high relative humidity
Symptoms
● Anthracnose is characterized by dark brown sunken spots on the pods.
● Dark reddish brown lesions appear along the underside veins of a leaf.
● Spread: Its spread through rain splash, wind-blown rain and movement of insects, animals and man, especially when plant foliage is moist.
● Sources of infection: Infected seed and crop debris
Control
● Use of certified seeds
● Crop rotation with non-host such as maize for at least 2 years
● Removal of crop debris after harvest
● Plant resistant varieties
● Avoid use of overhead irrigation
● Seed dressing with appropriate fungicide to control infection
● Spray with protective and systemic fungicides
Angular leaf spot (ALS)
● Conditions: Infection and disease development favoured by humid conditions and moderate temperatures (20-250C)
Symptoms:
● The disease starts with round lesions which usually appear as grey spots and later turn brown.
● The spots are enclosed by leaf veins, giving the spot a typical angular shape.
● On the stem and pods, round spots may appear but in severe cases the leaves fall. Infected pods may bear poorly developed, shriveled or discoloured seeds.
● Source of infection: Plant debris and infected volunteer plants
● Spread: contaminated equipment, clothing, splashes of water and windblown rain.
Control
● Crop rotation with non-host crop e.g maize for at least 2 years
● Removal or deep ploughing of crop debris
● Seed dressing with suitable fungicides
● Avoid movement in the bean in the bean fields when plants are wet
● Plant resistant varieties
● Growing of bean variety mixtures including resistant ones to reduce the spread of infection
Common bacterial blight (CBB)
Leaf spots
Water soaked pods
● Distribution: disease favoured by warm to high temperatures and high humidity
● Symptoms: water soaked spot at underside of leaves. The spots later enlarge to form large brown irregular lesions surrounded by a narrow yellow zone.
● Pods have sunken circular spots which are water-soaked initially but later dry with a reddish brown narrow border
● Sources of infection: Seed; infected dry beans debris and infected volunteer plants
● Spread: water splash; wind-blown rain; overhead irrigation; insects and contaminated equipment and clothing
Control
● Use disease free seeds- especially certified seeds
● Use resistant varieties
● Chemical seed dressing with copper based fungicides
● Crop rotation with non-legumes for about 3 years
● Deep ploughing infested debris to ensure destruction of pathogen
● Avoid visiting fields when wet
Halo blight
● Conditions: The disease is favoured by cool temperatures (16-200C), moist and cloudy conditions. Not common in areas with high temperatures
Symptoms
● Starts with small watery spots on the underside of leaves surrounded.
● The spots gradually become yellow green and the entire leaf turns yellow.
● Oval greasy water-soaked spots occur on pods which become sunken reddish/brown in colour
● Sources of infection: Infected seeds and plant debris
● Spread: Through water splash, windblown rain, contact among plants due to movement of people when leaves are wet
Water soaked spots on pods
● Practice crop rotation with non-leguminous crops for 2-3 years
● Uproot and destroy infected plants/ volunteers by burning
● Disinfect farm tools in sodium hypochlorite solution.
● Apply copper based fungicides
Bean common mosaic virus (BCMV)
BCMV disease. Source: Infonet biodivision
● Condition: Favored by temperature range 20-25 °C
Symptoms
● Cupping and twisting of leaves with a light and dark green mosaic pattern.
● The dark green tissue is often bubbled and/or in bands next to the veins.
● Small, curled pods with a greasy appearance and yields are reduced (up to 90%)
● Sources of infection: Infected seeds.
● Spread: It is transmitted by several aphid species.
Control
● Plant resistant varieties
● Plant certified seeds
● Early planting to help escape high aphid population period
● Destroy alternative hosts
● Control attacks of aphids
● Remove infected plants from the field
● Beans are ready for harvesting 70-120 days after sowing depending on varieties
● Harvest beans when all the pods have turned yellow, but before they have become so dry that the pods begin to shatter or rot away in the field.
● One can tell when the beans are dry by the loud, sharp noise they make when dropped on the ground.
Drying
● Dry harvested pods in the sun by spreading on tarpaulin or jute bags.
● If experiencing a spell of rain late in the season once pods have matured, plants can be removed from ground and hung upside down indoors or corridors to allow drying to continue.
Testing moisture content before threshing
● Test the moisture of the seed before threshing using teeth or pinching the seed with fingers.
● Dry beans should crack with a loud sound when bitten and not brittle. Brittle beans should be dried further.
Methods of testing bean seed moisture before threshing
Threshing
● Dried beans can be piled inside jute bags and hit with sticks slowly to split them open without damaging the seeds
Manual threshing of beans on a tarpaulin
● Use mechanized bean threshers for faster threshing and winnowing.
Mechanized bean thresher
Winnowing and sorting
● Winnow and sort the dry grains to remove chaff, dust, foreign matter such as stones, broken grains, shrivelled, mouldy, insect damaged, rotten discoloured or faded, and any remaining plant parts grains.
● The grains are winnowed in windy times to remove the chaff and clean the grains
Drying the Grain before storage
● Dry the grain by spreading on mats or tarpaulin under direct sun.
● Turn the grain regularly to ensure uniformity in dryness.
● Drying can also be done in a solar drier if available. A small greenhouse covered with polythene and fitted with drying trays can be constructed for faster drying of beans
Solar drier
● Test the moisture of the grain to make sure it is within the moisture content of 12% before packaging.
● Moisture content testing can be done using either moisture meter or salt moisture testing methods
Moisture meter
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