Horticultural News January - February issue

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! Plant potatoes in a site where tomatoes or other crops belonging to the same family as potatoes have not been planted during the previous two seasons. This helps to reduce the spread of soil borne diseases and pests. Land preparation Prepare the land well and early enough before the start of the rains. Make furrows in straight lines, 8-10 cm deep. Fertilizers and manure Farmers should perform a soil test regularly so as to get an indication of how much fertilizer and manure to use. a general recommendation, which depends on the fertility of the land, is to apply Diammonium phosphate (DaP) fertilizer at the rate of 200 kg/acre. The fertilizer should be mixed with the soil after application to avoid contact with the seed which can lead to ‘burning’ of the sprouts. Only well decomposed manure should be used so as to avoid the spread of a disease called rhizoctonia. The application rate is 2-4 tonnes/acre. 30 Growing potatoes successfully Potato (Solanum tuberosum L.) is variously referred to as Irish potato, English potato or round potato. Other names are viazi or viazi mviringo in Kiswahili. It is an important staple food in Kenya. Table or ware potatoes refer to potatoes that are grown for consumption as opposed to seed potatoes. Such potatoes can be boiled, fried, baked, mashed or made into chips or crisps. They can also be eaten in salads, stews or in mixed foods such as bananas, beans, maize and rice. There many potato recipes available. By LUNG’AHO C, NyONGESA M, KARINGA J and KINyAE, P M Choice of varieties a large number of potato varieties are grown in Kenya. The varieties differ in time of maturity, yield, appearance, cooking and marketing qualities and resistance to various diseases and pests as well as growth habit and tolerance to moisture stress. Growers are therefore advised to choose the correct variety for their intended use and growing conditions. a list of some of the varieties is shown in the following table. Key: Maturity period: Early (less than 90 days), Medium early (91-100 days), Medium late (101-110), Medium late (111-120 days), Late (121-130 days), Very late (More than 131 days) yields: Low (Less than 20t/ha), Medium (21-30 t/ha), High (31-40 t/ ha) and very high (More than 40 t/ha) H O R T I C U LT U R A L N E W S I j a n u a r y - F E B r u a r y 2 0 1 2 Characteristics of some of the commonly grown potato varieties Variety Skin Shape Maturity Yield Utilization Colour Period Boiling Chipping Chipping Asante Red Round Medium Very Fair Good Fair early high Red Oval Early Medium Good Good Good Red Round Medium late Medium Good Good Fair Red Round Late High Good Good Good Desiree Dutch Robijn Kenya Karibu Kenya Mavuno Kenya Mpya Kenya Sifa Kenya Sherehekea Purple Gold Tigoni White White Red White Purple White Round Oval Round Round Round Round Late Medium early Late Late Late Medium High High High Very high Medium Very high Good Good Good Good Good Good Good Good Good Good Good Fair Good Good Good Good Good Good
Sources of seed Farmers should use good quality seed to grow their potato crops. Certified seed potatoes are available from the KarI Seed unit, agricultural Development Corporations and other private seed multipliers. Farmers should consult their local agricultural officers on where to source for good quality seed. Seed size and sprouting The seeds should be the size of an egg (35-45 mm) and well sprouted with at least 4-5 sprouts per tuber to optimize yields. avoid seeds without sprouts, seeds with only one sprout or very old seed tubers because use of such seeds results in poor yields. Planting and spacing Plant seed tubers in furrows at a spacing of 75 cm between rows and 30 cm within rows (75 cm x 30 cm) with the sprouts facing up. Weeding and Ridging First weeding should be done 2-3 weeks after crop emergence while the second weeding should be done 2-3 weeks after the first weeding. Earthing-up helps the crop to form more tubers and also prevents greening of tubers. It should be done along the row during weeding. The final ridge should be approximately 25 cm high. Rotation Where possible, practice at least a 3 season rotation programme so as to sustainably grow the crop and reduce build-up of disease. Crops like maize and beans can be used. Pests and diseases ! Common Diseases Late blight: The disease usually appears as water soaked spots on the leaves and stems, which turn black. a white mould sometimes appears on the underside of the leaves. Control: use tolerant varieties and suitable fungicides. Bacterial wilt: The disease is characterized by wilting of plants even when the soil has enough water. It is spread by infected seed tubers or infected soil. Control: There is no chemical control yet. use disease free seed and suitable rotations. Infected plants and tubers together with the surrounding soil should be uprooted and burnt or buried in a deep pit. rhizoctonia diseases of potatoes (stem canker and black scurf): These diseases are caused by the fungus Rhizoctonia solani. The fungus causes considerable damage to emerging sprouts when growing conditions do not favour rapid emergence. The fungus forms dark brown to black hard masses on the surface of the tuber called sclerotia. Cankers may girdle the stems and result in aerial tuber formation, plant wilt and death. Infected plants may also produce many small tubers. Control. use good quality seed. Long crop rotations and use of well decomposed manure may also minimize incidence of the disease. application of suitable soil fungicides may also help. Viruses: Viruses disrupt the plants’ normal growing pattern and cause inefficient use of nutrients as well as reduced tolerance to other stresses. Some of the important viruses in the country are potato leaf roll virus, potato virus y, potato virus X and mosaics. Plants that are infected produce diseased tubers. Symptoms include chlorosis, dwarfing, leaf rolling, erectness, leaf deformations, crinkling and mosaics. Control: Viruses cannot be cured with chemicals. The best preventive method is planting only healthy seed tubers, elimination of infection sources and controlling vectors. Pests aphids: These are tiny insects that feed on the plants or tubers and spread virus diseases. Control: use appropriate insecticides both in the field and during storage. Potato tuber moth: This pest attacks potato plants by mining of foliage and on tubers. H O R T I C U LT U R A L N E W S I j a n u a r y - F E B r u a r y 2 0 1 2 31
Page 1 and 2: NO. 20 JAN/FEB 2012 Ksh 300, US$5 H
Page 3 and 4: H O R T I C U LT U R A L N E W S I
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Horticultural News January - February issue

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