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Potato
Scientific name:
Solanum tuberosum
Order/Family:
Solanales: Solanaceae
Local names:
Kiazi, egiasi, mbatata, potato, enkwashei (Kenya) / batata reno (Mozambique)
Pests and Diseases:
Aphids  Bacterial soft rot  Bacterial wilt  Cutworms  Early blight  Epilachna beetles  Late blight  Millipedes  Potato Spindle Tuber Viroid  Potato tuber moth  Root-knot nematodes  Scab  Storage pests  Viral diseases  Weeds 

Aphids (Myzus persicae, Macrosiphum euphorbiae, Aulacorthum solani, Aphis gossypii)

Many aphid species attack potatoes. The most important are the green peach aphid (Myzus persicae) the potato aphids (Macrosiphum euphorbiae, Aulacorthum solani) and the cotton aphid (Aphis gossypii).
Aphids are mainly found on young shoots on the underside of leaves. Feeding by aphids causes irregular curling of young potato leaflets and hinders growth of the leaflet. Potato aphids can attack potato sprouts in stores.
Direct damage caused by aphids sucking sap from the plant is usually of little importance. Most damage is caused by honeydew production on foliage and virus transmission.

Aphids are important pests as vectors of potato viruses such as the Potato Leaf Roll Virus, a serious disease affecting potatoes. Seed potatoes are particularly susceptible to this virus and even low aphid populations can be very damaging.

What to do:
  • Conserve natural enemies. They are important in natural control of aphids. (Link to natural enemies datasheet).
  • Control aphids in potato planted for seed production.
  • Site seed production areas in locations with low temperature, abundant rainfall and high wind velocity. Aphid populations are generally low under these conditions.
  • Within a potato growing area, locate seed potato fields upwind from commercial potato fields and alternative host crops to reduce dissemination of viruses through infected aphids.
  • Keep seed production areas separated from commercial potato production.
  • Check the field regularly. Monitoring of aphid build-up is important.
  • Protect young plants from aphid attack. Virus spread early in the season is more serious than later on, as young plants are generally more susceptible. Moreover, plants that are infected early become more efficient sources for further virus spread than plants infected later in the season.
  • Harvest seed potatoes no later than 8 to 10 days after a critical aphid build-up or increased virus infection rates are noted. This may help to avoid infection since the virus requires time to infect the tubers after a virus-carrying aphid has fed on potato foliage.
  • Remove yellow flowering weeds and any other host plants within and around the field. Aphids are attracted to yellow colour.
  • Protect potato tubers during storage by preventing access of aphids. Potato aphids readily colonise tuber sprouts. Seed potatoes are very susceptible to infection at this stage.
  • Neem products are useful for reducing aphid populations on potatoes. In Sudan, two applications of seed extracts at a rate of one kg seed kernels/40l water at a 14 days interval reduced aphid (A. gossypii) population to 60% compared to the control (Zebitz, 1995).
  • Extracts of the weed Artemisia vulgaris have also shown toxicity to potato aphids (Metspalu and Hiiesar, 1994).
Aphids
© Magnus Gammelgaard

Bacterial soft rot (Erwinia carotovora pv. carotovora / E.c. pv. atroseptica)

The bacteria enters through wounds and cause extensive rotting of potatoes due to degradation of tuber cell walls, often reducing tubers to a smelly pulp. They may also be carried over on tubers, and shoots (stems) emerging from infected tubers. These are blackened and commonly referred as blackleg, and the affected stems subsequently die.

What to do:
  • Use resistant varieties where available. This constitutes the best management strategy.
  • Use healthy seed tubers and avoid injury to the tubers.
  • Avoid excess watering.
  • Store and transport tubers in dry, well ventilated conditions.
  • Practice field hygiene.
Soft rot on carrot
© Oregon State University

Bacterial wilt (Ralstonia solanacearum)

Bacterial wilt can be very destructive at the lower altitude, warmer extreme of the potato's range in Kenya. This disease causes rapid wilting and death of the entire plant without any yellowing or spotting of leaves. All branches wilt at about the same time. The pathogen is transmitted through tuber seed into the soil. Also infested soil can be important source of disease inoculum (infection).

What to do:
  • Use clean certified disease-free seed.
  • Plant resistant varieties where available.
  • Remove wilted plants to reduce spread of the disease from plant to plant.
  • Bio-fumigation (incorporating especially mustard or radish plants in large amounts into the soil immediately before planting tomatoes or potatoes) helps in reducing and the long-term elimination of bacterial diseases from the soil. This practice is reported to reduce incidence of bacterial wilt by 50 to 70% in the Philippines (ACIAR 2005/6). For more information on biofumigation click here
  • Do not grow crops belonging to the same family as potatoes (e.g. tomatoes; peppers; or eggplant) in succession in the same land. Rotation is not effective against bacterial wilt because the pathogen can survive for several years in the soil and also can infect a wide range of crops and weeds. However, the disease incidence can be reduced if crop rotation with non-susceptible crops is combined with the other above-mentioned control components.
Bacterial wilt
© Courtesy of EcoPort, www.ecoport.org

Bacterial …

Bacterial …

Cutworms (Agrotis spp)

Cutworms are caterpillars of some moths. The caterpillars live in the soil and eat into tubers boring a wide shallow hole. They are also serious pests of newly sprouted potato plants, and can leave great empty patches in a potato field.

What to do:
  • Protect plants by wrapping them with collars. A simple collar can be made from cardboard tubes from paper towels or toilet paper (cut to size). This practice is time consuming, but it is effective and practicable in small fields.
  • If necessary spray neem extracts. Neem leaf extracts and neem seed extracts (1 kg/40 l water) have been effective against cutworms attacking potatoes reducing damage significantly in Sudan.
Cutworm
© A.M. Varela, icipe

Early blight (Alternaria solani)

Leaf spots of early blight are circular, up to 12 mm in diameter, brown, and often show a circular pattern.

On the potato tuber early blight results in surface lesions that appear a little darker than adjacent healthy skin. Lesions are usually slightly sunken, circular or irregular, brown and vary in size up to 1-2 cm in diameter. There is usually a well defined and sometimes slightly raised margin between healthy and diseased tissue. Internally, the tissue shows a brown to black corky, dry rot, usually not more than 6 mm. Deep cracks may form in older lesions.

Early blight thrives best under warm wet conditions.

What to do:
  • Use certified disease-free seeds
  • When using own seeds, hot water treat the seeds. For more information on hot water treatment click here
  • Practice rotation with non-solanaceaous crops.
  • Practice good field hygiene. Remove infected leaves during the growing season discard all badly infected potato plant debris at the end of each season.
  • Avoid overhead irrigation and lay down a thick organic mulch to prevent soil splashing onto lower leaves.
Early blight on potato tubers
© Chad Behrendt. Reproduced from University of Minnesota Extension.

Epilachna beetles (Epilachna spp.)

Several species of Epilachna beetles feed on the leaf tissue in between the veins leaving a network of veins intact. The adult beetles are oval, about 6 mm in length and reddish brown to brownish yellow in colour with black spots on their backs. They look very similar to the beneficial ladybird beetles (predators), but the body of this pest ladybird beetle is covered with short, light coloured hairs, which give them a non-glossy or matt appearance.

They lay eggs in clusters (20 to 50 eggs), usually on the underside of the leaves and placed vertically. The larvae (grubs) are pale yellow and easily recognisable by the strong branched spines covering their body. Generally, these beetles are minor pests of potatoes, but occasionally the infestation is so severe that control measures are needed.

What to do:
  • Handpick and destroy adults and larvae of Epilachna beetles. This is feasible in small plots.
  • Spray neem extracts. Simple neem-based pesticides have been reported to control Epilachna beetles on several crops. Thus, sprays with an aqueous neem seed extract (10g/l) at 10 days intervals showed repellent effect on these beetles in India. In Togo, feeding by Epilachna beetles in squash and cucumber could be reduced significantly by weekly applications of aqueous neem kernel extracts at concentrations of 25, 50 and 100 g/l and neem oil applied with an ultra-low-volume (ULV) sprayer at 10 and 20 l/ha (Ostermann and Dreyer, 1995).
Epilachna beetle
© A. M. Varela, icipe

Late blight (Phytophthora infestans)

This disease is favoured by cool, cloudy, wet conditions. Symptoms of late blight are irregular, greenish-black, water soaked patches, which appear on the leaves. The spots soon turn brown and many of the affected leaves wither, yet frequently remain attached to the stem.

What to do:
  • Plant resistant varieties where available. In Kenya, varieties "Tigoni", "Kenya Baraka", "Roslin Eburu", "Annet" and "Asante" are claimed to have some resistance to late blight.
  • Practice rotation with non-solanaceaous crops (do not rotate with tomatoes and eggplants).
  • Practice good field hygiene. Pull up and discard infected plants.
  • Select only, certified, disease-free seed potatoes and never plant table-stock potatoes
  • Keep foliage dry; avoid overhead irrigation.
  • Plant potatoes in sunny, well-drained locations.
  • KARI has also conducted studies to evaluate lower cost measures used by farmers to control Late blight, including the application of a mixture made of stinging nettle (possibly Urtica massaica, though not indicated) and Omo (presumably the commercial brand of laundry detergent). Although this treatment was not as effective as a commercial fungicide, Ridomil, blight scores were nevertheless lower and yields higher than observed for the control. On a benefit to cost basis, the stinging nettle treatment was impressive, at over two to one (KARI 2000, p. 83). This treatment is apparently not a common practice in Kenya, at least not yet, but an example of using stinging nettle (Urticaria dioica) as a treatment against late blight in Sweden is reported in Ecology and Society.
Late blight
© Thorsten Kraska, University of Bonn, Germany. Reproduced from the Crop Protection Compendium, 2004 Edition. © CAB International, Wallingford.

Late bligh…

Late bligh…

Late bligh…

Millipedes or "thousand-legged worms"

Millipedes are not insects, but are related to them. They have many legs (30 to 400) with a hard-shelled, round segmented body. They are brown to blackish brown in colour. They move slowly and curl up when disturbed. Millipedes lay eggs singly or in clusters of 20 to 100 in the soil. They live in moist soil and congregate around the plants in soil that is rich in organic content. They dry out easily and die. Thus, they seek wet places, such as compost piles, leaves and other plant debris, to hide under during the day. They tunnel into potato tubers.

What to do:
  • Clear hiding places. Remove volunteer plants, crop residues, decaying vegetation, dead leaves, grass, compost piles, excess mulch or other similar debris. Litter under trees, abandoned termite hills, and neglected home nurseries can also harbour large populations of millipedes.
  • Eliminate wet areas
  • Trap millipedes. They like hiding during daytime. therefore they can be attracted by placing flat objects (such as pieces of plywood) on the ground collecting them subsequently.
Millipedes
© A. M. Varela, icipe

Potato Spindle Tuber Viroid (PSTVd)

It is particularly destructive for seed production. Potato plants severely infected are upright, stunted and much thinner than normal plants. Leaves of infected plants are smaller and may be grey or distorted. The affected stems are often more branched and branches are at very sharp angles to the stem. Symptoms are more obvious on tubers. Affected tubers are small, narrow and spindle shaped (oblong).
In some varieties tubers develop knobs and swellings. In other varieties eyes on tubers are numerous, shallow and more prominent, and affected tubers are often cracked. This viroid is easily mechanically transmitted. An infection can be introduced by sowing infected seed tubers, by insects such as aphids, grasshoppers and flea beetles, and through pollen. Tomato and capsicum are additional hosts for PSTVd.

What to do:
  • Plant certified disease-free seed tubers.
  • Plant whole seed tubers instead of cut pieces.
  • Remove infected plants from the field.

The potato tuber moth (Phthorimaea operculella)

This moth is the most serious pest of potatoes in the region. It occurs in Africa wherever potatoes are grown, and it also attacks tobacco, eggplants and tomatoes. The moth is small (measuring about one mm at rest and with 12 to 16 mm wingspan), brownish grey in colour with narrow fringed wings. The moths are active mainly at dusk, but occasionally they can be seen flying within potato plants. Female moths lay eggs singly or in small batches on sheltered places of the foliage (leaf and stems) and near the eye buds on exposed tubers through cracks in the soil or in the store.

The caterpillars are up to 12 mm long and whitish to pale greenish in colour. They feed as leafminers between the upper and the lower epidermis and bore into the petiole, or a young shoot or main leaf vein and later into the tuber. When eggs are laid on tubers, caterpillars begin feeding on the tubers immediately upon hatching. They pupate in a silken cocoon covered with soil particles and debris among dead potato leaves, soil litter, eyes of tubers, and storage walls and floors.

Caterpillars burrowing in the tubers cause major damage by making long irregular black tunnels filled with excreta, where disease-causing microorganisms grow. These tunnels provide an entry point for various plant pathogens and make the potatoes unfit for human consumption. The pest is transferred with the harvested tubers to the potato store, where it can reproduce and infest other tubers. This may lead to total destruction of the stored crop.

What to do:
  • Conserve natural enemies. They are important for natural control of the potato tuber moth. Ladybird beetles prey on eggs and young caterpillars. Larvae of lacewings, big-eyed bugs, ground beetles, earwigs and rove beetles prey on all stages of the pest. Several native parasitic wasps attack this pest. A granulosis virus has also been found infecting caterpillars in the field (diseased caterpillars have a milky white colouration and are sluggish). However, in many cases control is not satisfactory, therefore several parasitic wasps, native from South America, the area of origin of the pest, have been introduced to several countries in Africa. The most important are Copidosoma koehleri and Apanteles subandinus. These wasps have provided effective control of the pests in several countries, particularly in Southern and Eastern Africa
  • Use healthy, clean seed, since infested seed tubers are the main cause of re-infestation in the field.
  • Avoid planting in rough soil. Plant as deeply as possible (10 cm deep) and ridge at least three times during the growing season. Experiments in Sudan showed that increasing the sowing depth from 2.5 cm practiced by farmers to 7.6 cm, significantly reduced damage by the cutworms and the potato tuber moth and resulted in an increase of 3.7 t/ha in marketable yield (Siddig, 1987).
  • Ensure compact hilling. This is very important to prevent moths reaching the tubers to lay eggs. It also makes it difficult for caterpillars to reach the tubers. In addition, emerging moths from infested tubers will not be able to emerge through deep soil.
  • Provide enough water to prevent soil cracks.
  • Mulch the plants with rice straw and/or with leaves. Mulching with neem leaves during the last four weeks before harvest significantly reduced insect damage in Sudan. (Ali, 1993).
  • Intercrop potatoes with hot pepper, onions or peas.
  • Harvest the crop immediately as it matures, as tubers left in fields for longer periods are highly infested.
  • At harvesting, ensure that the tubers are not exposed to moths before they are properly protected in the store. All harvested tubers have to be bagged and removed before late afternoon every day.
  • Destroy all infested potatoes immediately and remove all plant residues from the field. Caterpillars pupate in the tubers and dry stems left in the field.
  • Destroy all volunteer potato plants before planting new potato crops.
  • Use alternative pesticides to protect potatoes in store.
  • Neem can be applied to reduce damage by the potato tuber moth. For instance, in India a four months protection was achieved when harvested potatoes and the covering material were sprayed with five and 10% enriched neem seed extract (Saxena, 1995). In Sudan spraying neem seed and leaf extracts (1 kg/40 l water) and then placing tubers in jute sacks reduced post harvest losses by the potato tuber moth compared with traditional methods such as leaving the tuber unprotected or covering them with banana leaves only (Siddig, 1987). A neem seed extract was also effective for control of the potato tuber moth on potatoes in a store in Egypt (Salem, 1991) . Storage loss after 6 months in potatoes treated with 100ppm neem oil was 25% (compared to 10% with the insecticide carbaryl). Adults from larvae treated with neem oil were deformed. Work in Yemen confirmed the beneficial effect of neem; neem oil and sunflower oil halted the development of caterpillars of the potato tuber moth in storage. However, caution is needed since the oil seemed to interfere with potato respiration, leaving the potatoes very soft with dark tissue (Kroschel, 1995).
  • A Bt (Bacillus thuringiensis) preparation in powder form mixed with fine sand (1:25) dusted was very effective in controlling this pest in the store in Yemen and Kenya (Kroschel, 1995). Tuber infestation was also reduced by bedding the potatoes in the leaves of the Peruvian pepper tree (Schinus molle), also known as mpilipili in Swahili, and Eucalyptus sp. (Kroschel, 1995).
  • Storing potatoes in layers with branches of lantana is recommended by KIOF in areas where this pest is present Lantana is reported to repel tuber moths.
  • Application of plenty of wood ash or diatomite earth may also prevent rapid build up of tuber moth.
Potato tuber moth
© J. Kroschel, CIP

Potato tub…

Potato tub…

Potato tub…

Parasitic …

Root-knot nematodes (Meloidogyne spp.)

Potatoes are very susceptible to root-knot nematodes. Root-knot nematodes prefer warm temperatures and are likely to become established in potato crops grown in relatively warm areas. Generally, they are not a major problem in cool climate potato production areas, but can become a problem when potatoes are grown intensively or rotated with other susceptible crops. Infested potato plants may show varying degrees of stunting, yellowing of leaves and a tendency to wilt under moisture stress. Roots have swellings or galls. Affected tubers have blisters or swellings.

On potato tubers, galls may or may not be produced on the tuber surface, depending on cultivars. When galls are produced, they appear as small, raised lumps above giving the skin a rough appearance. Galls may be grouped in a single area or scattered near the tuber eyes. Infestations are difficult to detect in freshly harvested potato tubers.

Symptoms may develop when tubers are stored, particularly when exported to warmer climates where nematode numbers can rapidly increase. Symptoms are most severe when crops are grown on sandy soils and warm climates above 25°C. Nematode attack reduces the quality, size and number of tubers.

Infested potatoes can become more susceptible to bacterial wilt, and symptoms are more severe when plants are also infected with fungal pathogens such as Verticillium and Rhizoctonia.

Root-knot nematodes are mainly spread in potato tubers and in infested soil. Egg masses may be transported into clean fields via soil adhering to farm machinery. Spread within fields occurs during cultivation and in water, during irrigation or natural drainage.

What to do:
  • Practice proper crop rotation (e.g. potato - brassicas - cereals).
  • Use mixed cropping or grow marigolds (Tagetes spp.) or sunn hemp (Crotalaria juncea).
  • Maintain high levels of organic matter in the soil (manure and compost).
  • Bio-fumigation (incorporating fresh plant mass, especially mustard or radish plants, in large amounts into the soil before planting tomatoes or potatoes) helps against root knot nematodes. Decomposing plant parts release compounds, which kill nematodes. Two weeks after incorporating plant material into the soil a new crop can be planted (phytotoxic effects are usual if the crop is planted before two weeks). For more information on biofumigation click here
Root-knot nematodes
© DAFF Archives, www.insectimages.org. Courtesy of www.ecoport.org

Root-knot …

Root-knot …

Fungal diseases and Scab

Black scurf (Rhizoctonia solani), powdery scab (Spongospora subterranea) and common scab caused by the bacterium (Streptomyces scabies).

These diseases may cause similar symptoms. Black scurf and scab cause skin blemishes (russeting; rough corky tissue) on tubers.

These lesions may be so numerous as to involve the entire surface of affected tubers. Such lesions spoil the appearance of the tubers and cause waste in peeling and reduction in grade. These fungi live in the soil and survive in infected tubers. In most cases infection occurs whilst the tubers are still in the ground.

What to do:
  • Practice crop rotation.
  • In case of scab use healthy certified seed tubers.
  • Disinfect seed tubers from infected field through heat-treatment (10 min in water at 55°C). The same treatment of naturally or artificially contaminated seed tubers gave complete absence of blackleg infection in the field and decreased the amounts of powdery scab (Spongospora subterranea) and black scurf (Rhizoctonia solani) on progeny tubers. For more information on heat treatment click here
  • Avoid excessive liming and continuous cropping with potatoes.
  • Maintain soil pH at about 4.8 if continuous cropping cannot be avoided.
Scab
© www.ecoport.org

Viral diseases

Viral diseases of importance include:

  • Potato Leaf Roll Virus (PLRV)
  • Potato X Potexvirus (PVX)
  • Potato Virus Y Potyvirus (PVY)
  • Potato Spindle Tuber Viroid (PSTVd)

Under field conditions, there is often a composite infection with the three viruses (PLRV; PVX; PVY) and it becomes very difficult to distinguish the three on the basis of symptoms.
These viruses are transmitted by aphids. PVX causes distinct leaf mottling and crinkling. PVY causes dwarfing of plants, with a rough, mosaic appearance to the leaves and affected plants give a poor crop of small tubers. PVY is also tuber-borne. Potatoes infected with PLRV show an upward and inward rolling of leaflet margins and plants are dwarfed. Affected leaflets become thick and dry, and the lower leaves may become completely brown. Infected plants produce tubers smaller in size and numbers. PLRV also infects other solanaceous crops and weeds (e.g. tomato, tobacco, jimson weed).

What to do:
  • Use virus-free seed tubers.
  • Plant resistant varieties where available. In Kenya, the following potato varieties are claimed to possess some resistance to viral diseases: "Kenya Baraka", "Roslin Eburu", "Feldelslohn", "Annet" and "Dutch Robjn".
  • Uproot infected plants plants to reduce the incidence of infection and spread of the disease within a field. For maximum effectiveness remove the diseased plant, the three plants on each side of the diseased plant in the same row, and the three closest plants in adjacent rows. This is most important in seed fields.
  • Control insect vectors. This may reduce virus spread.
  • Control of insect vectors may reduce virus spread.
  • Do not overlap potato crops.
  • Practice good field sanitation.
  • Control nightshades and volunteer potatoes because these plants are reservoirs for viruses

Weeds

The major weeds in potato crops are annuals. Weeds can reduce yields through direct competition for light, moisture and nutrients. They may harbour pests and diseases that attack potatoes. Early season competition of weeds is very critical. When properly grown, the crop normally covers the ground and smothers any weed competition. Weeds present at harvest increase mechanical damage to the tubers, and reduce harvesting efficiency by slowing down harvesting operations and leaving undug tubers in the ground. The most important weed in potatoes worldwide is pigweed or fat hen (Chenopodium album).

What to do:
  • Practice crop rotation. Rotation of two or three years is an important strategy to control perennial weeds. Weeds tend to thrive with crops of similar growth requirements as their own and may benefit from practices directed to the crop. When diverse crops are used in a rotation, weed germination and growth cycles are disrupted by variation in cultural practices associated with each crop.
  • Control weeds early in the season. It is important to stop broadleaved weeds or annual grasses from appearing above the crop and competing strongly for nutrients and moisture when tubers are enlarging.
Pigweed
© Photography courtesy of Western Weeds CD-ROM. Web version by R. Randall. www.ecoport.org
General Information and Agronomic Aspects
Geographical Distribution of Potato in Africa
Potato originated in the highlands of South America, where it has been consumed for more than 8000 years. Spanish explorers brought the plant to Europe in the late 16th century as a botanical curiosity. By the 19th century it had spread throughout the continent, providing cheap and abundant food.
The potato arrived in Africa around the turn of the 20th century. British farmers introduced it to East Africa in the 1880s.The potato has grown in importance - both as a staple food and as a source of farmer incomes in medium to high altitudes in Kenya over the past 30 years.
Nearly all of Kenya's potatoes are consumed locally, at an average rate of almost 25 kg per capita a year. Potato is relished not only by the rural people who grow them, but by higher-income urban dwellers as well - while in some African countries potato is considered a "poor person's food", in Kenya it is considered a high quality and prestigious food item.











Nutritive Value per 100 g of edible Portion
Raw or Cooked Vegetable Food
Energy
(Calories / %Daily Value*)		 Carbohydrates
(g / %DV) 		Fat
(g / %DV) 		Protein
(g / %DV) 		Calcium
(g / %DV) 		Phosphorus
(mg / %DV) 		Iron
(mg / %DV) 		Potassium
(mg / %DV) 		Vitamin A
(I.U)		 Vitamin C
(I.U)		 Vitamin B 6
(I.U)		 Vitamin B 12
(I.U)		 Thiamine
(mg / %DV) 		Riboflavin
(mg / %DV) 		Ash
(g / %DV)
Potato baked (flesh and skin) 93.0 / 5% 21.2 / 7% 0.1 / 0% 2.5 / 5% 15.0 / 1% 70.0 / 7% 1.1 / 6% 535.0 / 15% 10.0 IU / 0% 9.6 / 16% 0.3 / 16% 0.0 / 0% 0.1 / 4% 0.0 / 3% 1.3
Potatoes cooked in skin (with skin) 78.0 / 4% 17.2 / 6% 0.1 / 0% 2.9 / 6% 45.0 / 4% 54.0 / 5% 6.1 / 34% 407 / 12% 0.0 / 0% 5.2 / 9% 0.2 / 12% 0.0 / 0% 0.0 / 2% 0.0 / 2% 2.0
Red Potato baked (flesh and skin) 89.0 / 4% 19.6 / 7% 0.2 / 0% 2.3 / 5% 9.0 / 1% 72.0 / 7% 0.7 / 4% 545 / 16% 10.0 IU / 0% 12.6 / 21% 0.2 / 11% 0.0 / 0% 0.1 / 5% 0.1 / 3% 1.3
Sweet Potato baked in skin 90.0 / 5% 20.7 / 7% 0.2 / 0% 2.0 / 4% 38.0 / 4% 54.0 / 5% 0.7 / 4% 475 / 14% 19217 IU / 384% 19.6 / 33% 0.3 / 14% 0.0 / 0% 0.1 / 7% 0.1 / 6% 1.3
Sweet Potato cooked without skin 76.0 / 4% 17.7 / 6% 0.1 / 0% 1.4 / 3% 27.0 / 3% 32.0 / 3% 0.7 / 4% 230.0 / 7% 15741 IU / 315% 12.8 / 21% 0.2 / 8% 0.0 / 0% 0.1 / 4% 0.0 / 3% 0.6
*Percent Daily Values are based on a 2000 calorie diet. Your daily values may be higher or lower, depending on your calorie needs.


Climatic conditions, soil and water management

 Potato requires well-distributed rainfall of 500 to 750 mm in a growing period of 3 to 4.5 months. Most commercial cultivars of potato tuberise (form tubers) best in cool climates with night temperatures below 20°C. Optimum day temperatures are within the range of 20 to 25°C. Short daylengths (12 to 13 hours) lead to earlier maturity. In the short daylength conditions of the tropics and subtropics, maximum yields can usually be obtained in cool highland areas and in cooler seasons. Cultivation is concentrated in highland areas from 1200 to 3000 m above sea level.In regions with a critical dry season, planting early in the rainy season is best. If the rainy season is long and excessive, time of planting is usually towards the end of the rainy season.

Potato is tolerant of a rather wide variety of soils, except heavy, waterlogged clays. Good drainage is of great importance. Impermeable layers in the soil limit rooting depth and the amount of available water, and so greatly reduce yields. Deep soils with good water retention and aeration give best growth and yields. The most suitable soil pH is between 4.8 and 6. At higher pH, tubers are liable to suffer from scab disease.

Propagation
Potato is normally propagated vegetatively by small (40 to 100 g) tubers, called 'seed tubers' or 'seed potatoes'. It can also be propagated by pieces of tuber ('seed pieces') or by true seed. The seed rate (tubers) ranges from 1.5 to 4.0 t/ha. The first problem facing growers in developing countries is obtaining supplies of healthy planting material of a suitable cultivar at an acceptable price. Some countries undertake traditional propagation of the seed tubers on sites in the highlands with suitable cool but frost-free climates and where the population of insect vectors of diseases can be kept at an adequately low level.

Recently, the use of true potato seed for propagation has aroused great interest. True seed does not transmit most of the potato diseases, is very light and is easy to transport. Promising methods to grow potatoes from true seed include raising seedlings in a nursery and transplanting them to the field.

Planting
In regions with a critical dry season, planting early in the rainy season is best. If the rainy season is long and excessive, time of planting is usually towards the end of the rainy season. Potato subjected to heavy rainfall during growth or harvest is prone to diseases.

Tubers planted to produce potatoes for consumption should generally be planted in rows 75-100 cm apart with a spacing of 30 to 40 cm within the row (25 to 44,000 plants per ha). The closer spacing should be used in fertile soils and good rainfall areas to avoid the production of very large tubers. Seed potatoes are planted at a spacing of 15 to 20 cm within the row (about 80,000 plants per ha).

Potatoes are planted at a depth of 5 to 15 cm (measured from the top of the tuber). Planting depth is greater under warm, dry conditions than under cool, wet conditions. Shallow plantings should be avoided, because the lower nodes of the stem must remain covered to encourage tuberisation (tuber initiation) and to avoid greening of tubers and tuber moth damage. Earthing up or hilling is carried out to control weeds and to avoid greening of the tubers. Potatoes are normally planted by hand in developing countries, but mechanical planters are available.

Plough-under or incorporate available organic manures in the soil before planting to enhance the water-holding capacity and texture of the soil as well as to provide enough nutrients for a healthy crop. A high yielding potato crop under conventional farming removes 95 to 140 kg N/ha, 35 kg P/ha, 125 to 170 kg K (Potassium)/ha and has relatively high needs for Mg (Magnesium) and Mn (Manganese). Organic farmers will need to identify organic sources for similar amounts of nutrients. Potatoes respond well to large amounts of compost or well-rotted animal manures.
Fertiliser recommendations based on soil analysis offer the very best chance of getting the right amount of fertilizer without over or under fertilising. Ask for assistance from the local agriculturist office for soil sampling and soil analysis procedures.

Sources of seed potatoes
In Kenya certified healthy seed potatoes are available from KARI Research Station, Ol Joro Orok and Tigoni Research Station (CIP).

Varieties in Kenya and their characteristics
Variety Yield Storage Drought resistance Late blight Viruses Maturity Eco-zone
"Kenya Baraka" High Good Some resistance Some resistance Some resistance Medium Medium High
"Roslin Eburu" Medium High Very good Resistant Some resistance Some resistance Medium Medium High
"Feldelslohn" High Fairly good Some resistance Very susceptlible Some resistance Medium late High
"Annet" High Good Some resistance Some resistance Some resistance Early High Medium Low
"Dutch Robjn" High Very good Some resistance Susceptible Some resistance Medium High Medium
"Roslin Tana" High Fair Some tolerance - - Medium High Medium
"Roslin Gucha" Medium Good Tolerant - - Medium High Medium
"Desiree" Medium Fairly good Some tolerance - - Medium High Medium
"Roslin Ruaka" High Good Some tolerance - - Medium High Medium
"Cardinal" Medium Good Some tolerance - - Medium High Medium
"Pimpernel" Medium Good Some tolerance - - Medium High
"Arka" High Good Tolerant - - Medium High Medium
"Kerr's Pink" Medium Good Tolerant - - Medium High Medium

Note:
High eco-zone = 2300m altitude
Medium = 1500-2300m altitude
Low = below 1500m altitude
High yield = 12-15 tons/ha
Medium yield = 8-10 tons/ha
Low yield = 4-6 tons/ha
(Source: Ministry of Agriculture & Rural Development and Japan International Development Agency (2000)).


Adoption of potato varieties (CIP Nairobi)
Total area harvested in hectares (Has) in 2005: 120,842

Variety Name Estimated area harvested (%) Trend in area* Strengths of variety Weakness of variety Main uses of variety
"Tigoni" 30 Increasing High yielding, resistant to late blight, big tubers Sensitive to bacteria wilt Market
"Nyayo" 25 Declining Early maturing, tasty Sensitive to late blight Market, home use
"Ngure" 8 Increasing High price, early maturing, tasty Sensitive to late blight Market and home use
"Tana Kimande" 7 Increasing Big tubers, good price Low yields, late maturing Market
"Asante" 6 Increasing High yielding, resistant to late blight, big tubers Not good for mashing Market
"Dutch Robijn" 5 Increasing Storage long, crisping Sensitive to late blight Market/ Crisps
"Kerr's Pink" 3 Declining High price, early maturing, tasty Sensitive to late blight Market, home use
"Desiree" 3 Constant Storage long, tasty Sprout very early Market
"Tigoni Red" 3 Increasing High yielding, resistant to late blight Sprout very early Market
"Komesha" 2 Constant High yield Sensitive to bacterial wilt Market
"Meru Mugaruro" 2 Increasing High yield, big tubers Sensitive to late blight and bacterial wilt Market
"Roslin Tana" 2 Declining Good for chips Low yields, sensitive to late blight Market
Others 4 Increasing - - Home, market
(Source of estimate: CIP)

Husbandry
Adequate control of weeds is required to ensure high yields. In the tropics, manual weeding is generally practised in small-scale production, but herbicides are sometimes used in large-scale production.

Potato responds well to high soil fertility. Manure or compost is needed if the land has been continuously cropped. Well-decomposed animal manure or compost is recommended.
Ridging soon after emergence helps control weeds, prevents greening of developing tubers and prevents spores of late blight fungus from reaching the tubers.

Intercropping
Wide ridges or mounds are required for intercropping. Potatoes can be intercropped with a wide range of annual crops such as sweet potato, maize or even pyrethrum. Potatoes planted in rotation or intercropped with barley, maize, peas, or wheat prevent soil exhaustion. In this case, intercrops are planted at the bottom or at the edge of the furrows and the potatoes in the ridge.

However in order to get full benefit from a potato crop such as high yields, weed suppression and ease of management, without building up high levels of soil borne diseases: it is recommended to grow potatoes in a separate field and rotate the crop with others. Interplanting with a short season legume such as beans can increase total crop yield and help prevent spread of diseases.

Crop rotation
Avoid planting potatoes in the same field for several consecutive seasons. Proper crop rotation enhances soil fertility, increases soil organic matter, conserves soil moisture and helps maintain soil structure. In addition, it avoids build-up of soil-borne pathogens affecting potato, and reduces the level of soil infestation once the soil has been contaminated. Rotations should not include crops that are common hosts for diseases and pests of potatoes (e.g. tomato, eggplant, pepper). Rice, maize and legumes are recommended for crop rotation practices. Planting brassicas such as broccoli, cabbage and mustard plants before the potato crop helps reducing incidence of bacterial wilt and nematodes. Control volunteer potatoes and weeds in the rotation crop.

Harvesting
Time of harvesting of potato varies with cultivar, cultural practices, climate and price. Tubers harvested while still immature tend to have low dry matter content and to suffer more skin damage, resulting in easier infection by fungal and bacterial pathogens. However, seed potatoes are often harvested early, to avoid virus infection that may occur during the latter part of the growing season. Late blight attack may also be a reason for early harvesting.
The harvesting operation involves destroying the aboveground parts (haulm), lifting and collecting the tubers. A general practice to avoid excess mechanical damage of tubers at harvesting is to cut the tops 10 to 14 days before lifting the potatoes to give them time to develop matured and hardened skins. The haulm is destroyed either by manual or mechanical cutting.

In small-scale farming in the tropics, lifting is done manually using simple implements such as sticks, hoes and spades. Mechanical harvesting is carried out only in large-scale farming areas using various types of potato diggers, for example, ploughs, spinners or elevator diggers. Semi-automatic diggers lift the tubers from the soil for hand-picking or collection. Harvesting should not be done during or immediately after rain.

Yield
In 1996, the average yield of storage potato tubers throughout the world was about 16 tonnes per hectare (t/ha). Average yields (t/ha) for different continents in 1996 were: Asia (14.5), Africa (11.3), North America (39.1), South America (12.6), Europe (16.2) and Oceania (28.8). In many tropical and subtropical regions potential yields are much higher than actual yields due to constraints (environmental, seasonal, propagation, crop protection, economic and social) that prevent the full expression of this potential, but individual farmers in Kenya have reported yields up to 35 t/ha.

Post harvest handling
Harvesting or any other handling to which potato tubers are subjected may cause damage ranging from external injury to internal bruising. After harvesting it is advantageous to allow the tubers to dry in heaps for about 1 to 2 weeks at 10 to 20°C (or in cold store) under high humidity before further handling. During this time the skin hardens, wounds heal, adhering soil dries and disease symptoms become more visible, which facilitates the removal of the infected tubers. Grading should not be started before the curing and hardening have taken place, otherwise further damage occurs. If the hardening has taken place in the soil before harvesting, grading for sale can be done immediately to avoid greening and sprouting.

Before the tubers go into storage, rotten and infected tubers, which may become sources of post-harvest disease infection, should be removed. Potato tubers are usually delivered into stores in bags, baskets or crates. To facilitate handling, containers should not be too large; if they are large they should not be filled completely. Storage of ware potatoes for the market is associated with undesirable quality changes (mainly sprouting, high sugar content, and weight loss due to evaporation and respiration). For short-term storage (1-2 weeks) in the tropics, ware potatoes may be stored at ambient temperatures in the dark, in well-ventilated buildings. Small-scale farmers can keep potatoes in on-farm storage using inexpensive, well-ventilated constructions.

Storing of seed potatoes
After cold storage, seed potatoes should be pre-sprouted in diffuse light to ensure optimal development of sprouts prior to planting. By storing seed tubers in diffused light at ambient temperatures, excessive sprouting is avoided and seed potatoes can be kept in good physiological condition for a long period of time. If potatoes are stored in bulk without cold storage in the tropics for more than a couple of weeks, they completely loose appeal and will start rotting.
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Fresh Quality Specifications for the Market in Kenya
The following specifications constitute raw material purchasing requirements

© S. Kahumbu, Kenya

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Information on Pests and Weeds

Root-knot nematodes (Meloidogyne spp.)

Potatoes are very susceptible to root-knot nematodes. Root-knot nematodes prefer warm temperatures and are likely to become established in potato crops grown in relatively warm areas. Generally, they are not a major problem in cool climate potato production areas, but can become a problem when potatoes are grown intensively or rotated with other susceptible crops. Infested potato plants may show varying degrees of stunting, yellowing of leaves and a tendency to wilt under moisture stress. Roots have swellings or galls. Affected tubers have blisters or swellings.

On potato tubers, galls may or may not be produced on the tuber surface, depending on cultivars. When galls are produced, they appear as small, raised lumps above giving the skin a rough appearance. Galls may be grouped in a single area or scattered near the tuber eyes. Infestations are difficult to detect in freshly harvested potato tubers.

Symptoms may develop when tubers are stored, particularly when exported to warmer climates where nematode numbers can rapidly increase. Symptoms are most severe when crops are grown on sandy soils and warm climates above 25°C. Nematode attack reduces the quality, size and number of tubers.

Infested potatoes can become more susceptible to bacterial wilt, and symptoms are more severe when plants are also infected with fungal pathogens such as Verticillium and Rhizoctonia.

Root-knot nematodes are mainly spread in potato tubers and in infested soil. Egg masses may be transported into clean fields via soil adhering to farm machinery. Spread within fields occurs during cultivation and in water, during irrigation or natural drainage.

Root-knot nematodes
Root-knot nematodes Meloidogyne incognita damage on potato

© DAFF Archives, www.insectimages.org. Courtesy of www.ecoport.org


More Information on Root-knot nematodes
What to do:
  • Practice proper crop rotation (e.g. potato - brassicas - cereals).
  • Use mixed cropping or grow marigolds (Tagetes spp.) or sunn hemp (Crotalaria juncea).
  • Maintain high levels of organic matter in the soil (manure and compost).
  • Bio-fumigation (incorporating fresh plant mass, especially mustard or radish plants, in large amounts into the soil before planting tomatoes or potatoes) helps against root knot nematodes. Decomposing plant parts release compounds, which kill nematodes. Two weeks after incorporating plant material into the soil a new crop can be planted (phytotoxic effects are usual if the crop is planted before two weeks). For more information on biofumigation click here

Aphids (Myzus persicae, Macrosiphum euphorbiae, Aulacorthum solani, Aphis gossypii)

Many aphid species attack potatoes. The most important are the green peach aphid (Myzus persicae) the potato aphids (Macrosiphum euphorbiae, Aulacorthum solani) and the cotton aphid (Aphis gossypii).
Aphids are mainly found on young shoots on the underside of leaves. Feeding by aphids causes irregular curling of young potato leaflets and hinders growth of the leaflet. Potato aphids can attack potato sprouts in stores.
Direct damage caused by aphids sucking sap from the plant is usually of little importance. Most damage is caused by honeydew production on foliage and virus transmission.

Aphids are important pests as vectors of potato viruses such as the Potato Leaf Roll Virus, a serious disease affecting potatoes. Seed potatoes are particularly susceptible to this virus and even low aphid populations can be very damaging.

Aphids
Green peach aphids (Myzus persicae) on pepper leaf. Adult wingless females are oval-bodied, 1-2 mm in body length, of very variable colour.

© Magnus Gammelgaard
More Information on Aphids
What to do:
  • Conserve natural enemies. They are important in natural control of aphids. (Link to natural enemies datasheet).
  • Control aphids in potato planted for seed production.
  • Site seed production areas in locations with low temperature, abundant rainfall and high wind velocity. Aphid populations are generally low under these conditions.
  • Within a potato growing area, locate seed potato fields upwind from commercial potato fields and alternative host crops to reduce dissemination of viruses through infected aphids.
  • Keep seed production areas separated from commercial potato production.
  • Check the field regularly. Monitoring of aphid build-up is important.
  • Protect young plants from aphid attack. Virus spread early in the season is more serious than later on, as young plants are generally more susceptible. Moreover, plants that are infected early become more efficient sources for further virus spread than plants infected later in the season.
  • Harvest seed potatoes no later than 8 to 10 days after a critical aphid build-up or increased virus infection rates are noted. This may help to avoid infection since the virus requires time to infect the tubers after a virus-carrying aphid has fed on potato foliage.
  • Remove yellow flowering weeds and any other host plants within and around the field. Aphids are attracted to yellow colour.
  • Protect potato tubers during storage by preventing access of aphids. Potato aphids readily colonise tuber sprouts. Seed potatoes are very susceptible to infection at this stage.
  • Neem products are useful for reducing aphid populations on potatoes. In Sudan, two applications of seed extracts at a rate of one kg seed kernels/40l water at a 14 days interval reduced aphid (A. gossypii) population to 60% compared to the control (Zebitz, 1995).
  • Extracts of the weed Artemisia vulgaris have also shown toxicity to potato aphids (Metspalu and Hiiesar, 1994).

Cutworms (Agrotis spp)

Cutworms are caterpillars of some moths. The caterpillars live in the soil and eat into tubers boring a wide shallow hole. They are also serious pests of newly sprouted potato plants, and can leave great empty patches in a potato field.

Cutworm
Cutworm (Agrotis sp.) Early instars are about 7-12 mm long. Fully grown caterpillars are 35-50 mm long.

© A.M. Varela, icipe
More Information on Cutworms
What to do:
  • Protect plants by wrapping them with collars. A simple collar can be made from cardboard tubes from paper towels or toilet paper (cut to size). This practice is time consuming, but it is effective and practicable in small fields.
  • If necessary spray neem extracts. Neem leaf extracts and neem seed extracts (1 kg/40 l water) have been effective against cutworms attacking potatoes reducing damage significantly in Sudan.

The potato tuber moth (Phthorimaea operculella)

This moth is the most serious pest of potatoes in the region. It occurs in Africa wherever potatoes are grown, and it also attacks tobacco, eggplants and tomatoes. The moth is small (measuring about one mm at rest and with 12 to 16 mm wingspan), brownish grey in colour with narrow fringed wings. The moths are active mainly at dusk, but occasionally they can be seen flying within potato plants. Female moths lay eggs singly or in small batches on sheltered places of the foliage (leaf and stems) and near the eye buds on exposed tubers through cracks in the soil or in the store.

The caterpillars are up to 12 mm long and whitish to pale greenish in colour. They feed as leafminers between the upper and the lower epidermis and bore into the petiole, or a young shoot or main leaf vein and later into the tuber. When eggs are laid on tubers, caterpillars begin feeding on the tubers immediately upon hatching. They pupate in a silken cocoon covered with soil particles and debris among dead potato leaves, soil litter, eyes of tubers, and storage walls and floors.

Caterpillars burrowing in the tubers cause major damage by making long irregular black tunnels filled with excreta, where disease-causing microorganisms grow. These tunnels provide an entry point for various plant pathogens and make the potatoes unfit for human consumption. The pest is transferred with the harvested tubers to the potato store, where it can reproduce and infest other tubers. This may lead to total destruction of the stored crop.

Potato tuber moth
Potato tuber moth adult (Phthorimaea operculella) is about 12-16mm long.

© J. Kroschel, CIP


What to do:
  • Conserve natural enemies. They are important for natural control of the potato tuber moth. Ladybird beetles prey on eggs and young caterpillars. Larvae of lacewings, big-eyed bugs, ground beetles, earwigs and rove beetles prey on all stages of the pest. Several native parasitic wasps attack this pest. A granulosis virus has also been found infecting caterpillars in the field (diseased caterpillars have a milky white colouration and are sluggish). However, in many cases control is not satisfactory, therefore several parasitic wasps, native from South America, the area of origin of the pest, have been introduced to several countries in Africa. The most important are Copidosoma koehleri and Apanteles subandinus. These wasps have provided effective control of the pests in several countries, particularly in Southern and Eastern Africa
  • Use healthy, clean seed, since infested seed tubers are the main cause of re-infestation in the field.
  • Avoid planting in rough soil. Plant as deeply as possible (10 cm deep) and ridge at least three times during the growing season. Experiments in Sudan showed that increasing the sowing depth from 2.5 cm practiced by farmers to 7.6 cm, significantly reduced damage by the cutworms and the potato tuber moth and resulted in an increase of 3.7 t/ha in marketable yield (Siddig, 1987).
  • Ensure compact hilling. This is very important to prevent moths reaching the tubers to lay eggs. It also makes it difficult for caterpillars to reach the tubers. In addition, emerging moths from infested tubers will not be able to emerge through deep soil.
  • Provide enough water to prevent soil cracks.
  • Mulch the plants with rice straw and/or with leaves. Mulching with neem leaves during the last four weeks before harvest significantly reduced insect damage in Sudan. (Ali, 1993).
  • Intercrop potatoes with hot pepper, onions or peas.
  • Harvest the crop immediately as it matures, as tubers left in fields for longer periods are highly infested.
  • At harvesting, ensure that the tubers are not exposed to moths before they are properly protected in the store. All harvested tubers have to be bagged and removed before late afternoon every day.
  • Destroy all infested potatoes immediately and remove all plant residues from the field. Caterpillars pupate in the tubers and dry stems left in the field.
  • Destroy all volunteer potato plants before planting new potato crops.
  • Use alternative pesticides to protect potatoes in store.
  • Neem can be applied to reduce damage by the potato tuber moth. For instance, in India a four months protection was achieved when harvested potatoes and the covering material were sprayed with five and 10% enriched neem seed extract (Saxena, 1995). In Sudan spraying neem seed and leaf extracts (1 kg/40 l water) and then placing tubers in jute sacks reduced post harvest losses by the potato tuber moth compared with traditional methods such as leaving the tuber unprotected or covering them with banana leaves only (Siddig, 1987). A neem seed extract was also effective for control of the potato tuber moth on potatoes in a store in Egypt (Salem, 1991) . Storage loss after 6 months in potatoes treated with 100ppm neem oil was 25% (compared to 10% with the insecticide carbaryl). Adults from larvae treated with neem oil were deformed. Work in Yemen confirmed the beneficial effect of neem; neem oil and sunflower oil halted the development of caterpillars of the potato tuber moth in storage. However, caution is needed since the oil seemed to interfere with potato respiration, leaving the potatoes very soft with dark tissue (Kroschel, 1995).
  • A Bt (Bacillus thuringiensis) preparation in powder form mixed with fine sand (1:25) dusted was very effective in controlling this pest in the store in Yemen and Kenya (Kroschel, 1995). Tuber infestation was also reduced by bedding the potatoes in the leaves of the Peruvian pepper tree (Schinus molle), also known as mpilipili in Swahili, and Eucalyptus sp. (Kroschel, 1995).
  • Storing potatoes in layers with branches of lantana is recommended by KIOF in areas where this pest is present Lantana is reported to repel tuber moths.
  • Application of plenty of wood ash or diatomite earth may also prevent rapid build up of tuber moth.

Epilachna beetles (Epilachna spp.)

Several species of Epilachna beetles feed on the leaf tissue in between the veins leaving a network of veins intact. The adult beetles are oval, about 6 mm in length and reddish brown to brownish yellow in colour with black spots on their backs. They look very similar to the beneficial ladybird beetles (predators), but the body of this pest ladybird beetle is covered with short, light coloured hairs, which give them a non-glossy or matt appearance.

They lay eggs in clusters (20 to 50 eggs), usually on the underside of the leaves and placed vertically. The larvae (grubs) are pale yellow and easily recognisable by the strong branched spines covering their body. Generally, these beetles are minor pests of potatoes, but occasionally the infestation is so severe that control measures are needed.

Epilachna beetle
Epilachna beetle (Epilachna spp.) and damage caused on water melon

© A. M. Varela, icipe
What to do:
  • Handpick and destroy adults and larvae of Epilachna beetles. This is feasible in small plots.
  • Spray neem extracts. Simple neem-based pesticides have been reported to control Epilachna beetles on several crops. Thus, sprays with an aqueous neem seed extract (10g/l) at 10 days intervals showed repellent effect on these beetles in India. In Togo, feeding by Epilachna beetles in squash and cucumber could be reduced significantly by weekly applications of aqueous neem kernel extracts at concentrations of 25, 50 and 100 g/l and neem oil applied with an ultra-low-volume (ULV) sprayer at 10 and 20 l/ha (Ostermann and Dreyer, 1995).

Millipedes or "thousand-legged worms"

Millipedes are not insects, but are related to them. They have many legs (30 to 400) with a hard-shelled, round segmented body. They are brown to blackish brown in colour. They move slowly and curl up when disturbed. Millipedes lay eggs singly or in clusters of 20 to 100 in the soil. They live in moist soil and congregate around the plants in soil that is rich in organic content. They dry out easily and die. Thus, they seek wet places, such as compost piles, leaves and other plant debris, to hide under during the day. They tunnel into potato tubers.

Millipedes
Potato tubers damaged by millipedes.

© A. M. Varela, icipe
What to do:
  • Clear hiding places. Remove volunteer plants, crop residues, decaying vegetation, dead leaves, grass, compost piles, excess mulch or other similar debris. Litter under trees, abandoned termite hills, and neglected home nurseries can also harbour large populations of millipedes.
  • Eliminate wet areas
  • Trap millipedes. They like hiding during daytime. therefore they can be attracted by placing flat objects (such as pieces of plywood) on the ground collecting them subsequently.

Weeds

The major weeds in potato crops are annuals. Weeds can reduce yields through direct competition for light, moisture and nutrients. They may harbour pests and diseases that attack potatoes. Early season competition of weeds is very critical. When properly grown, the crop normally covers the ground and smothers any weed competition. Weeds present at harvest increase mechanical damage to the tubers, and reduce harvesting efficiency by slowing down harvesting operations and leaving undug tubers in the ground. The most important weed in potatoes worldwide is pigweed or fat hen (Chenopodium album).

Pigweed
Pigweed (Chenopodium album)

© Photography courtesy of Western Weeds CD-ROM. Web version by R. Randall. www.ecoport.org
More Information on Weeds
What to do:
  • Practice crop rotation. Rotation of two or three years is an important strategy to control perennial weeds. Weeds tend to thrive with crops of similar growth requirements as their own and may benefit from practices directed to the crop. When diverse crops are used in a rotation, weed germination and growth cycles are disrupted by variation in cultural practices associated with each crop.
  • Control weeds early in the season. It is important to stop broadleaved weeds or annual grasses from appearing above the crop and competing strongly for nutrients and moisture when tubers are enlarging.
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Information on Diseases

Bacterial wilt (Ralstonia solanacearum)

Bacterial wilt can be very destructive at the lower altitude, warmer extreme of the potato's range in Kenya. This disease causes rapid wilting and death of the entire plant without any yellowing or spotting of leaves. All branches wilt at about the same time. The pathogen is transmitted through tuber seed into the soil. Also infested soil can be important source of disease inoculum (infection).

Bacterial wilt
Bacterial wilt of potato tuber

© Courtesy of EcoPort, www.ecoport.org


More Information on Bacterial wilt
What to do:
  • Use clean certified disease-free seed.
  • Plant resistant varieties where available.
  • Remove wilted plants to reduce spread of the disease from plant to plant.
  • Bio-fumigation (incorporating especially mustard or radish plants in large amounts into the soil immediately before planting tomatoes or potatoes) helps in reducing and the long-term elimination of bacterial diseases from the soil. This practice is reported to reduce incidence of bacterial wilt by 50 to 70% in the Philippines (ACIAR 2005/6). For more information on biofumigation click here
  • Do not grow crops belonging to the same family as potatoes (e.g. tomatoes; peppers; or eggplant) in succession in the same land. Rotation is not effective against bacterial wilt because the pathogen can survive for several years in the soil and also can infect a wide range of crops and weeds. However, the disease incidence can be reduced if crop rotation with non-susceptible crops is combined with the other above-mentioned control components.

Bacterial soft rot (Erwinia carotovora pv. carotovora / E.c. pv. atroseptica)

The bacteria enters through wounds and cause extensive rotting of potatoes due to degradation of tuber cell walls, often reducing tubers to a smelly pulp. They may also be carried over on tubers, and shoots (stems) emerging from infected tubers. These are blackened and commonly referred as blackleg, and the affected stems subsequently die.

Soft rot on carrot
Bacterial soft rot caused by (Erwinia carotovora var. carotovora) (here on carrot)

© Oregon State University
What to do:
  • Use resistant varieties where available. This constitutes the best management strategy.
  • Use healthy seed tubers and avoid injury to the tubers.
  • Avoid excess watering.
  • Store and transport tubers in dry, well ventilated conditions.
  • Practice field hygiene.

Late blight (Phytophthora infestans)

This disease is favoured by cool, cloudy, wet conditions. Symptoms of late blight are irregular, greenish-black, water soaked patches, which appear on the leaves. The spots soon turn brown and many of the affected leaves wither, yet frequently remain attached to the stem.

Late blight
Symptoms of late blight (Phytophthora infestans) on potato stem.

© Thorsten Kraska, University of Bonn, Germany. Reproduced from the Crop Protection Compendium, 2004 Edition. © CAB International, Wallingford.


More Information on Late blight
What to do:
  • Plant resistant varieties where available. In Kenya, varieties "Tigoni", "Kenya Baraka", "Roslin Eburu", "Annet" and "Asante" are claimed to have some resistance to late blight.
  • Practice rotation with non-solanaceaous crops (do not rotate with tomatoes and eggplants).
  • Practice good field hygiene. Pull up and discard infected plants.
  • Select only, certified, disease-free seed potatoes and never plant table-stock potatoes
  • Keep foliage dry; avoid overhead irrigation.
  • Plant potatoes in sunny, well-drained locations.
  • KARI has also conducted studies to evaluate lower cost measures used by farmers to control Late blight, including the application of a mixture made of stinging nettle (possibly Urtica massaica, though not indicated) and Omo (presumably the commercial brand of laundry detergent). Although this treatment was not as effective as a commercial fungicide, Ridomil, blight scores were nevertheless lower and yields higher than observed for the control. On a benefit to cost basis, the stinging nettle treatment was impressive, at over two to one (KARI 2000, p. 83). This treatment is apparently not a common practice in Kenya, at least not yet, but an example of using stinging nettle (Urticaria dioica) as a treatment against late blight in Sweden is reported in Ecology and Society.

Early blight (Alternaria solani)

Leaf spots of early blight are circular, up to 12 mm in diameter, brown, and often show a circular pattern.

On the potato tuber early blight results in surface lesions that appear a little darker than adjacent healthy skin. Lesions are usually slightly sunken, circular or irregular, brown and vary in size up to 1-2 cm in diameter. There is usually a well defined and sometimes slightly raised margin between healthy and diseased tissue. Internally, the tissue shows a brown to black corky, dry rot, usually not more than 6 mm. Deep cracks may form in older lesions.

Early blight thrives best under warm wet conditions.

Early blight on potato tubers
Early blight results in surface lesions that appear a little darker than adjacent healthy skin. Lesions are usually slightly sunken, circular or irregular, and vary in size up to 2 cm in diameter. There is usually a well defined and sometimes slightly raised margin between healthy and diseased tissue. Internally, the tissue shows a brown to black corky, dry rot, usually not more than 6 mm. Deep cracks may form in older lesions.

© Chad Behrendt. Reproduced from University of Minnesota Extension.
More Information on Early blight
What to do:
  • Use certified disease-free seeds
  • When using own seeds, hot water treat the seeds. For more information on hot water treatment click here
  • Practice rotation with non-solanaceaous crops.
  • Practice good field hygiene. Remove infected leaves during the growing season discard all badly infected potato plant debris at the end of each season.
  • Avoid overhead irrigation and lay down a thick organic mulch to prevent soil splashing onto lower leaves.

Fungal diseases and Scab

Black scurf (Rhizoctonia solani), powdery scab (Spongospora subterranea) and common scab caused by the bacterium (Streptomyces scabies).

These diseases may cause similar symptoms. Black scurf and scab cause skin blemishes (russeting; rough corky tissue) on tubers.

These lesions may be so numerous as to involve the entire surface of affected tubers. Such lesions spoil the appearance of the tubers and cause waste in peeling and reduction in grade. These fungi live in the soil and survive in infected tubers. In most cases infection occurs whilst the tubers are still in the ground.

Scab
Scab symptoms (here on citrus leaf)

© www.ecoport.org
What to do:
  • Practice crop rotation.
  • In case of scab use healthy certified seed tubers.
  • Disinfect seed tubers from infected field through heat-treatment (10 min in water at 55°C). The same treatment of naturally or artificially contaminated seed tubers gave complete absence of blackleg infection in the field and decreased the amounts of powdery scab (Spongospora subterranea) and black scurf (Rhizoctonia solani) on progeny tubers. For more information on heat treatment click here
  • Avoid excessive liming and continuous cropping with potatoes.
  • Maintain soil pH at about 4.8 if continuous cropping cannot be avoided.

Viral diseases

Viral diseases of importance include:

  • Potato Leaf Roll Virus (PLRV)
  • Potato X Potexvirus (PVX)
  • Potato Virus Y Potyvirus (PVY)
  • Potato Spindle Tuber Viroid (PSTVd)

Under field conditions, there is often a composite infection with the three viruses (PLRV; PVX; PVY) and it becomes very difficult to distinguish the three on the basis of symptoms.
These viruses are transmitted by aphids. PVX causes distinct leaf mottling and crinkling. PVY causes dwarfing of plants, with a rough, mosaic appearance to the leaves and affected plants give a poor crop of small tubers. PVY is also tuber-borne. Potatoes infected with PLRV show an upward and inward rolling of leaflet margins and plants are dwarfed. Affected leaflets become thick and dry, and the lower leaves may become completely brown. Infected plants produce tubers smaller in size and numbers. PLRV also infects other solanaceous crops and weeds (e.g. tomato, tobacco, jimson weed).




What to do:
  • Use virus-free seed tubers.
  • Plant resistant varieties where available. In Kenya, the following potato varieties are claimed to possess some resistance to viral diseases: "Kenya Baraka", "Roslin Eburu", "Feldelslohn", "Annet" and "Dutch Robjn".
  • Uproot infected plants plants to reduce the incidence of infection and spread of the disease within a field. For maximum effectiveness remove the diseased plant, the three plants on each side of the diseased plant in the same row, and the three closest plants in adjacent rows. This is most important in seed fields.
  • Control insect vectors. This may reduce virus spread.
  • Control of insect vectors may reduce virus spread.
  • Do not overlap potato crops.
  • Practice good field sanitation.
  • Control nightshades and volunteer potatoes because these plants are reservoirs for viruses

Potato Spindle Tuber Viroid (PSTVd)

It is particularly destructive for seed production. Potato plants severely infected are upright, stunted and much thinner than normal plants. Leaves of infected plants are smaller and may be grey or distorted. The affected stems are often more branched and branches are at very sharp angles to the stem. Symptoms are more obvious on tubers. Affected tubers are small, narrow and spindle shaped (oblong).
In some varieties tubers develop knobs and swellings. In other varieties eyes on tubers are numerous, shallow and more prominent, and affected tubers are often cracked. This viroid is easily mechanically transmitted. An infection can be introduced by sowing infected seed tubers, by insects such as aphids, grasshoppers and flea beetles, and through pollen. Tomato and capsicum are additional hosts for PSTVd.




What to do:
  • Plant certified disease-free seed tubers.
  • Plant whole seed tubers instead of cut pieces.
  • Remove infected plants from the field.
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Information Source Links
  • Acland, J.D. (1980). East African Crops. FAO / Longman. ISBN: 0 582 60301 3
  • Ali, M.A (1993). Effects of cultural practices on reducing field infestation of potato tuber moth (Phthorimaea operculella) and greening of tubers in Sudan. Journal of Agricultural Science, 121(2): 187-192; 19 ref.
  • Berg, G. (2006). Agriculture notes. Root-knot nematode on potatoes. AG0574. ISSN 1329-8062. State of Victoria, Department of Primary Industries.
  • Bohlen, E. (1973). Crop pests in Tanzania and their control. Federal Agency for Economic Cooperation (bfe). Verlag Paul Parey. ISBN: 3-489-64826-9.
  • CAB International (2005). Crop Protection Compendium, 2005 edition. Wallingford, UK www.cabi.org
  • CIP Nairobi (2005). Estimates of Currently grown potato cultivars.
  • Centipedes and millipedes. Later's Pest Info Bulletin. www.laters.com
  • Department for Environment, Food and Rural Affairs (DEFRA) (2002). Meloidogyne chitwoodi (the Columbia root-knot nematode) and Meloidogyne fallax www.defra.gov.uk
  • Godfrey,L. D., Davis, U.C., Haviland, D. R.(2003). UC Pest Management Guidelines. How to Manage Pests. Potato Aphids, green peach aphid (Myzus persicae), potato aphid (Macrosiphum euphorbiae)]. UC IPM Pest Management Guidelines: Potato. UC ANR Publication 3463. Insects. UC Cooperative Extension, Kern Co. (Reviewed 6/03, updated 6/03). Statewide IPM Program, Agriculture and Natural Resources, University of California.
  • International Year of the potato www.potato2008.org
  • Karren, J. B. Millipedes. Fact sheet No. 21. Revised April 2000. extension.usu.edu
  • Kfir, R. (2003). Biological control of the potato tuber moth Phthorimaea opercullela in Africa. In: Neuenschwander, P. - Biological Control in IPM Systems in Africa.
  • Kroschel, J. (1995). Integrated pest management in potato production in the Republic of Yemen- with special reference to the integrated biological control of the potato tuber moth (Phthorimaea operculella Zeller). Tropical Agriculture 8.GTZ. Margraf Verlag. ISBN: 3-8236-1242-5.
  • Ministry of Agriculture and Rural Development (Kenya) & Japan International Cooperation Agency (2000). Local and Export Vegetables Growing Manual. Reprinted by Agricultural Information Resource Centre, Nairobi, Kenya. 274 pp.
  • Nutrition Data www.nutritiondata.com.
  • Oisat. Organisation for Non-Chemical Pest Management in the Tropics. www.oisat.org
  • Ostermann, H. and Dreyer, M. (1995). Neem Products for Pest management. Vegetables and grain legumes. In: The Neem tree Azadirachta indica A. Juss. and other meliaceous plants sources of unique natural products for integrated pest management, industry and other purposes? Edited by H. Schmutterer in collaboration with K. R. S. Ascher, M. B. Isman, M. Jacobson, C. M. Ketkar, W. Kraus, H. Rembolt, and R.C. Saxena. VCH. pp. 392-403. ISBN: 3-527-30054-6.
  • Potatoes. Kenya Overview research.cip.cgiar.org
  • Saxena, R. C. (1995). Neem Products for Pest management. Pest of stored products. In: The Neem tree Azadirachta indica A. Juss. and other meliaceous plants sources of unique natural products for integrated pest management
  • Zebitz, C. P. W. (1995). Neem Products for Pest management. Root and Tuber Crops. In "The Neem tree Azadirachta indica A. Juss. and other meliaceous plants sources of unique natural products for integrated pest management, industry and other purposes". (1995). Edited by H. Schmutterer in collaboration with K. R. S. Ascher, M. B. Isman, M. Jacobson, C. M. Ketkar, W. Kraus, H. Rembolt, and R.C. Saxena. VCH. pp. 403-407. ISBN: 3-527-30054-6.
  • Zitter, T.A., Gallenberg, D.J. (2002). Virus and viroid diseases of potato. Department of Plant Pathology, Cornell University. www.vegetablemdonline.ppath.cornell.edu
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Contact Information
  • Corner Shop cls@mitsuminet.com
  • Food Network East Africa Ltd info@organic.co.ke 0721 100 001
  • Green Dreams admin@organic.co.ke 0721 100 001
  • Kalimoni Greens kalimonigreens@gmail,com 0722 509 829
  • Karen Provision Stores karenstoresltd@yahoo.com 020885552
  • Muthaiga Green Grocers
  • Nakumatt Supermarket info@nakumatt.net 020551809
  • Uchumi Supermarket
  • Zuchinni Green Grocers 0204448240
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Potato Solanum tuberosum - Tuberous roots and leaves.
© Arnoldo Mondadori Editore SpA (www.ecoport.org)
Transplanting
Transplanting is the planting of uprooted seedlings grown in seedbeds or in nurseries, in a permanent location where they will continue to grow
Crop rotation
Crop rotation is the practice of growing different crops in succession on the same land.
Diameter
Thickness or width.
Mulch
Plant material such as straw, leaves, crop residues, green manure crops, saw-dust etc. that is spread upon the surface of the soil. A mulch cover helps protect the soil from erosion and evaporation, nourishes soil life, increases soil organic matter content and provides nutrients to the crop.
Herbicide
Herbicide is a material used specifically to manage and prevent damage caused by weeds.
Brassicaceae
Brassicaceae or Cruciferae, also known as the crucifers, the mustard family or cabbage family is a family of flowering plants. The name Brassicaceae is derived from the included genus Brassica. The family contains well-known species such as Brassica oleracea (cabbage, cauliflower...), Brassica rapa (turnip, Chinese cabbage...), Brassica napus (rapeseed...) and many more.
Organic manures
Manures derived from animal products or plant residues. They usually have considerable nitrogen content, and contain most other nutrients essential for plant growth.
Soil organic matter
Organic substances in the soil originating from animal and plant residues in various stages of decomposition and re-formation. Also referred to as humus
Fungi
Occurring worldwide, most fungi are largely invisible to the naked eye, living for the most part in soil, dead matter, and as symbionts of plants, animals, or other fungi. They perform an essential role in all ecosystems in decomposing organic matter and are indispensable in nutrient cycling and exchange. Some fungi become noticeable when fruiting, either as mushrooms or molds.

Fungi are responsible for a range of serious plant diseases such as blight, grey mould, bunts, powdery mildew, and downy mildew. Crops of all kinds often suffer heavy losses.

Fungal plant diseases are usually managed with applications of chemical fungicides or heavy metals. In some cases, conventional breeding has provided fungus resistantcultivars.

Besides combatting yield losses, preventing fungal infection keeps crops free of toxic compounds produced by some pathogenic fungi. These compounds, often referred to as mycotoxins, can affect affect the immune system and disrupt hormone balances. Some mycotoxins are carcinogenic.
IPM
A combination of chemical and biological control methods, based on the concept of economic tresholds. Pest management in organic farming uses many biological control methods developed as par of IPM.
Soil sampling
Soil sampling is the taking of small amounts of soil (5-15 cm below the topsoil) from several locations of a field. To prepare the soil samples for soil analysis, pulverize the big clumps and mix the soil thoroughly. About 2 cups of fine soil is needed for soil analysis
Fungi
Occurring worldwide, most fungi are largely invisible to the naked eye, living for the most part in soil, dead matter, and as symbionts of plants, animals, or other fungi. They perform an essential role in all ecosystems in decomposing organic matter and are indispensable in nutrient cycling and exchange. Some fungi become noticeable when fruiting, either as mushrooms or molds.

Fungi are responsible for a range of serious plant diseases such as blight, grey mould, bunts, powdery mildew, and downy mildew. Crops of all kinds often suffer heavy losses.

Fungal plant diseases are usually managed with applications of chemical fungicides or heavy metals. In some cases, conventional breeding has provided fungus resistantcultivars.

Besides combatting yield losses, preventing fungal infection keeps crops free of toxic compounds produced by some pathogenic fungi. These compounds, often referred to as mycotoxins, can affect affect the immune system and disrupt hormone balances. Some mycotoxins are carcinogenic.
Predator
Animal that attacks and feeds on other animals, such as an insect (e.g. ladybird beetle), bird or spider feeding on pest insects.
Resistance
Ability of a living organism not to get affected by a disease or pest; or of a pest not to be affected by a pesticide.

Pesticide Resistance is the ability of a life form to develop a tolerance to a pesticide. Pests (weeds, insects, mites, diseases, etc.) that become resistant to a pesticide will not be affected by the pesticide. When pests are resistant, it is more difficult to control the pest. Therefore, it is important to try to prevent pesticide resistance.
Resistance
Ability of a living organism not to get affected by a disease or pest; or of a pest not to be affected by a pesticide.

Pesticide Resistance is the ability of a life form to develop a tolerance to a pesticide. Pests (weeds, insects, mites, diseases, etc.) that become resistant to a pesticide will not be affected by the pesticide. When pests are resistant, it is more difficult to control the pest. Therefore, it is important to try to prevent pesticide resistance.
Cultivar
Cultivar is a plant variety. It is a group of similar plants which through their structural features and performance can be identified from other varieties within the same species.
Intercropping
Intercropping is the planting of two or more crops in the same field, usually planted in alternating rows or sections.
Cultivar
Cultivar is a plant variety. It is a group of similar plants which through their structural features and performance can be identified from other varieties within the same species.
Instar
Growth stages.
IPM
A combination of chemical and biological control methods, based on the concept of economic tresholds. Pest management in organic farming uses many biological control methods developed as par of IPM.
Symptom
Symptom - the plant's response to the disease causing organism, examples are; changes in plant color, death of infected tissues, and wilting. It is the external or internal physical characteristic of a disease as expressed by the host plant.
Microorganism
A microorganism is an organism that is microscopic (usually too small to be seen by the naked human eye). Microorganisms are very diverse. They include bacteria, fungi, archaea, and protists; microscopic plants (called green algae); and animals such as plankton, the planarian and the amoeba. Some also include viruses, but others consider these as non-living.