A-Z of soybean farming

Soya beans will do well in areas with an altitude of 0-2,00Om above sea level, rainfall of400mm per year and temperatures of15- 25 degrees Centigrade. The soils should be rich in calcium, well- drained and fertile with a pH of5.6-7.0.

Land should be prepared during the dry season to give time for the vegetation to rot and dry and also expose soil-borne pests to the sun. Ploughing should be done to medium tilth.

Planting:

Soya bean is propagated by use of seeds. Planting should be done at the onset of the rains. Plant one seed per hole at a spacing of 30cm between rows and15cm between seeds.

At planting, apply 200kg DAP/ha of fertiliser. The fertiliser should be applied in the planting hoe or furrow and mixed thoroughly with the soil before placing the seed. Apply 100kg CAN/ha as a top-dressing initially at the first trifoliate leaf stage and again at the onset of flowering. Application of foliar feed (Bayfolan or Rapid— grow) at fortnightly intervals from the fourth week post- planting to mid-podding phase also promotes higher yields. Use of farmyard manure is recommended especially where soils are low in organic matter. It should be applied in planting furrows or holes and mixed well with soil before planting at a rate of10 tonnes/ha.

Weed control

 Timely 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 crop should not be weeded at flowering time or when the field is wet to avoid flower shedding, spread of diseases and soil compaction.

Regular water supply is essential as lack of moisture affects yields. It also affects uniformity and quality. Water stress during flowering reduces yields.

Diseases

Rust: lt is caused by fungus and is a serious disease of beans. It is favoured by high humidity conditions. Characterised by presence of raised, small, white spots on the lower leaf surface, which turn red to dark brown after a few days.

Control: Crop rotation, use tolerant cultivars, chemical sprays like Baycor, Anil and Alto every two weeks before flowering and Dithane M45 during flowering.

Angular leaf spot:

 A fungal disease it is characterised by necrotic and well-defined lesions with typical angular shape. The lesions may then increase in size, coalesce and cause partial necrosis and yellowing of leaves. On primary leaves, lesions are usually round, larger than those found on trifoliate leaves and may develop concentric rings.

Control: Use healthy certified seeds, seed treatment using Fernasan, spraying the crop with Benomyl, Baycor, Kocide 101 and Dithane M45.

Root rots:

A fungal disease caused by Fusarium spp, Rhizoctonia spy and Sclerótium spp. Affected plants yellow and stems dry at the soil level. Stunting may also occur. Seedling establishment is poor, uneven growth, chlorosis and premature de- foliation of severely infected plants.

Control: Seed dressing with Fernasen—D and drenching of plants at vegetative stage with Benomyl, Brassicol or Bavistin.

Bacterial blight:

 It is caused by Pseudomonas phaseollcol- la and 7anffiomonas phase- oli. It is a serious disease of beans in Kenya, especially in cool and wet areas. The disease is spread through splashing from exuding lesions and plant debris. Affected plants show halos on the leaves, drying of leaf margins, yellowing and water-soaked pods.

Control: Use certified seeds, rouging and destruction of infected plants and spray fungicides with copper.

Anthracnose:

A fungal disease caused by Colletotri- chum lindemuthianurn.The Fungus is seed—borne and affects all aerial plant parts. The fungus is spread by rain splash, wind and mechanical contact and occurs in cool, damp weather. The disease is characterised by the appearance of sunken, brown spots with black edges on pods, while on leaves, there are angular brown spots and oblong stripes on stems.

Control: Use of certified seeds, field sanitation, crop rotation, resistant varieties and foliar sprays like Benomyl, Mancozed and Propineb.

 Bean Common Mosaic Virus

Symptoms of the disease vary with variety, stage of growth and environmental factors. The disease is seed—borne and transmitted by aphids. The symptoms include mosaic (mottling, curling and stunting of leaves), systemic necrosis and local malformations. The leaves may roll, become malformed and there is general stunting of the plant. The plant produces excessive number of lateral shoots.

Control: Use of° certified seeds, resistant cultivars, rouging of infected plants, control aphids.

Harvesting

Harvesting starts 70 days after planting for early-maturing varieties and up to 180 days for the others. Soya beans are ready for harvesting when the leaves start turning yellow or when one pod per plant turns brown or black. Yields range from 500- 1,000kg per hectare but with good management, higher yields can be attained.

 Dry grains should be stored when they have a moisture content of below 15 per cent and dressed with chemicals like Actellic 2per cent.

Pests

Root knot nematodes (Meloldo ne spp):

These attack roots causing lesions, galls or swellings, plant stunting and wilting of severely infected crops. The lesions also serve as entry points for bacteria and fungi. Affected plants are dwarfed and have distorted leaves.

Control: Crop rotation, good weed control as the plants also host nematodes, Wallow- ing infested fields and soil.

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

Bean thrips:  Damage is caused by nymphs and adults, which feed and puncture flower structures and young pods.

Control: Before flowering, foliar sprays using Diazinon starting from two leaf stage; during flowering, with Kara- te, Decís or Ambush CY.

Carol Mutua, Department of Crops Horticulture and Soils, Egerton University