Harvesting and Post Harvest Practises

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5 Harvesting and post -harvest practices

5.1 Harvesting

5.1.1 Determining the time of harvestIn order to determine the optimum time of harvest, the following factors could be considered:

• Variety’s growth duration and its capacity to be prolonged• Environmental conditions (water supply, soil condition, weather, etc)• Pest and disease incidence• Market demand• Market price• Need of land to plant the consecutive crop• Economic value of the consecutive crop

Sweetpotato roots are ready for harvesting between three to eight months after planting, oftenmuch sooner than other root and tuber crops. Most sweetpotato varieties are normallyharvested at five months after planting. Harvesting too early or too late can result in lowyields. If the crop is harvested too early the roots will not had enough time to develop to theirmaximum size. If the crop is harvested too late the storage roots may have become fibrous,and the chances of the roots having been attacked by sweetpotato weevils or diseases(particularly root rots) increases. In order to determine the optimum harvest time, farmersshould weigh the various factors listed above in the context of the prevailing conditions, andfind a balance between advantageous and disadvantageous factors, in relation to thepotential and needs of each individual farm enterprise.

5.1.2 Harvest ing methodsIn several places where sweetpotato is mainly grown basically for home consumption,staggered/ piecemeal harvesting is practiced, whereby a few large roots are dug up and takenback to the home for cooking while the other roots are left on the plants in the field, and willbe gradually be removed depending on the pattern of the households consumption. In East

Africa, women typically do the piecemeal harvesting, and they move around the field lookingfor cracks on the mounds or ridges, which they perceive as being indicative of a sizeable root.Mature roots are selected carefully during the harvesting and the earth is heaped up over theremaining ones to allow them to continue bulking, the heaping up of earth will also protect theroots from sun damage and reduce the chances of weevil access to them. Harvesting isusually done carefully with locally made sharp sticks, rods or machetes in order to avoidinjuring the remaining roots. Other farmers harvest all the roots from one area of the field atonce using a hand hoe. Some farmers use both methods. Farmers usually harvest enoughsweetpotato for one or more meals for one or two days. Piecemeal harvesting can start asearly as two/ three months after planting for some varieties. Farmers do not usually harvestlarge quantities at once, in order to avoid the roots rotting and being wasted. Harvesting alarge field all at once is usually only done when sweetpotato is destined for the market.

Different varieties respond differently to piecemeal harvesting; some produce larger or smallerroots as a result of it, some have a longer time period over which piecemeal harvesting canoccur. Varieties with longer maturity periods are usually more suitable for piecemealharvesting than varieties with short maturity periods where all the storage roots tend tomature at the same time.

The duration of piecemeal harvest varies by location and agro-ecology, harvesting can startfrom three to eight months after planting and might go on for a period of one to nine monthsdepending on the variety. Harvest duration is a function of different factors such as variety,soil type, availability of other foods, household size, disease and pest infestation, and weatherconditions. Under high sweetpotato weevil population pressure and during times of water

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stress, piecemeal harvesting could last only a month or less (as plants tend to dry up due todisturbance of the root system, weevils infest any exposed roots and necks through the soilcracks and multiply rapidly). At high altitudes with very low weevil population pressure,piecemeal harvesting can last for six to nine months.

In some areas where commercial sweetpotato growing is common, market competition results

in some sweetpotato roots being harvested before they are mature. In the humid tropical partsof East and Central Africa, it is possible to grow two crops of sweetpotato per year.

Harvesting of sweetpotato is mainly done manually and care needs to be taken to avoidwounding the roots during harvesting. After harvest the roots are usually sorted manually.Sorting involves the selection of roots into different lots based on shape, colour and otherphysical parameters. Sorting can take place at different levels (field, roadside, market,consumer, catering etc) depending on the intended use of the roots. The sweetpotato rootsare then usually covered with plant materials to protect them against direct sunshine whichcan cause shrinkage and shrivelling.

In some parts of the world such as Japan and China where sweetpotato commercialisation isadvanced, mechanical harvesters are used. In this case, vines are removed before

harvesting, then the roots are dug out by machine. The roots are sorted and loaded ontotrucks. In many cases, sorting is done by hand. The vines are cut off prior to harvesting theroots as this process allows the skin of the roots to become firmer making them lessvulnerable to bruising during harvesting.

Since the yields increase rapidly right up to the time the plant matures, harvesting beforematurity means a loss of market quality as well as yields.

5.1.3 Assessment of yield and crop valueIf farmers are able to assess the sweetpotato yield in their field and are informed about themarket price at harvest time, they will be in a stronger bargaining position with the traders. Anexperienced trader can estimate the number of roots in the soil by looking at just a few plants.Farmers need to be able to do the same in order to calculate the value of their crop and toensure they don’t sell it either directly from the field at a low value, or harvest it only todiscover the deal they agreed on is a poor one.

The quantity of storage roots in field can most easily be assessed by estimating the averageroot weight per plant and multiplying this by the number of plants in the field. Another way isto assess the average root weight per square meter and multiply this by the field area (in m2).The average root weight per plant or per square meter should be assessed by observing (andweighing if possible) a representative sample across the field. The second method usingweight per square meter is more difficult than the first one using weight per plant, particularlywhen the field has an irregular shape and the exact area is difficult to measure. Therefore,only the first method is discussed in detail here.

The weight of the roots sweetpotato plants produce can vary widely. Therefore it is necessaryto estimate the average weight of roots per plant. In order to do this we need to observe asample of at least 10 plants per 1,000-2,000 m 2 to represent the whole crop, this exampleassumes that the whole field is planted with the same variety of sweetpotato. These tenplants must be selected randomly across the field. Digging up and weighing the roots is themost reliable way to determine the weight per plant, but this is time consuming and might notbe acceptable to potential buyers. In that case, the soil covering the roots is partly removed toobserve the storage roots and estimate their total weight. Estimating the weight of roots in thesoil is a skill that can only be developed with practice. After having assessed the total sample,the average weight per plant is calculated by totalling the weight of the individual plants anddividing this by the total number of plants observed.

The plant population in the whole field can be determined by counting all productive plants,which is the most accurate way, but very time consuming. A simpler slightly less accurate wayis to determine the average number of plants per step along a ridge, hence to count the total

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number of steps across all ridges or mounds in the field. If the shape of the field is regular andallows easy division into equal parts, we only need to count the number of steps along theridges of half or quarter of the field, and then multiply that by two or four respectively and thenby the number of plants per step along the ridge to get a good estimate of the number ofplants in the whole field.

Example: A. Weight of roots per plantPlant 1 – 0.35 kgPlant 2 – 0.50 kgPlant 3 – 0.40 kgPlant 4 – 0.75 kgPlant 5 – 0.50 kgPlant 6 – 0.55 kgPlant 7 – 0.60 kgPlant 8 – 0.20 kgPlant 9 – 0.65 kgPlant 10 – 0.40 kg

If we work out the average weight of roots per plant, we add up the totalweight of the roots of the 10 plants, then divide the total by 10Total weight of roots of the ten plants = 4.9 kg

Divided by 10 = (4.9 ÷ 10) = 0.49 kg

So the average weight of roots per plant is 0.49kg

B. One step along a ridge contains 5 plants.C. The field can be divided into four equal parts; a quarter of the field contains 125 steps

along the ridges, which means the whole field contains 125 * 4 = 500 steps.D. If there are 5 plants per step, and there are 500 steps in the whole field there are 5 *

500 = 2,500 plants in the whole field. Each of these plants has an average rootweight of 0.49 kg, so the root weight of the whole field is 0.49 * 2,500 = 1,225 kg.

E. The total (underground) crop value can be calculated by multiplying the total harvest(kg) by the prevailing market price per kg of storage roots.

5.1.4 Packing and transport ing of freshly harvested sweetpotato rootsPacking of the roots is usually done in the field. Farmers commonly pack the roots andstrategically place the large roots at the top on the bag to quickly attract the buyer on firstsight. Packing should minimize deterioration of the roots within the container and cushionagainst impact and compression. During packing in the field care must be taken to minimisephysical damage that results from impact bruises due to stacking and overfilling of bags,abrasion or vibration bruises due to root movement against each other. Therefore packagesshould be neither loose (to avoid vibration bruising during transport) nor overfilled, and shouldprovide good aeration.

Sweetpotato does not require specialized transportation, and many options exist for movingroots from the field to market e.g. by head; bicycles, oxen. Some physical damage is likely tooccur with all these transportation methods, but in order to ensure quality care must be taken.

5.2 Post-harvest storage A major challenge to sweetpotato production is post-harvest handling. The crop is bulky andonce harvested has a short shelf life. The various storage techniques are presented below:

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5.3 Fresh storageMany farmers do not routinely store fresh sweetpotato roots, but leave them in the grounduntil required, where they are prone to attack by insect pests, disease and vertebrate pestssuch as rodents. It is possible to store fresh roots successfully in specially constructed pits orin mounds, or clamp stores. Losses can be kept to a minimum and roots can remain in arelatively ‘fresh’ state for three – five months.

Pit storage of sweetpotato Clamp storage of sweetpotato

5.3.1 Why sto re roots?Storing fresh sweetpotato roots in specially designed structures enables the farmer to benefitin a number of ways:

• roots can be harvested as soon as they mature so that the land can be madeavailable for other crops;

• storing good quality roots enables the family to eat fresh sweetpotato for a longerperiod after harvest than would normally be the case;

•

the stored ‘fresh’ roots can be sold for a high price in the off-season;• increased household food security;• the incidence of pest attack can be significantly reduced by harvesting the roots

before the build up of pests during the dry season ; and• good quality stored roots act as an emergency source of income during the dry

season when fresh roots are no longer available in the field.

5.3.2 Problems of sweetpotato sto rageSweetpotato roots are tender and decline rapidly in quality after harvest because:

• they can lose water and weight during storage, which adversely affects their textureand taste;

• diseases can cause losses in storage, for example, rotting and off-flavours;• pest attacks, especially from sweetpotato weevils, can cause serious damage;

Sweetpotato roots are low value and bulky so storage structures for fresh roots have to berelatively large and therefore may not be economical.

5.3.3 Good storage techniquesThere are three things that must be done to ensure successful storage of fresh sweetpotatoroots:

• carefully select only top quality roots without any signs of handling or pest or diseasedamage for storage

• keep them in specially designed stores• check the stores at regular intervals

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5.3.4 Root selectionCareful and strict selection of roots intended for storage is very important. Only completelyundamaged roots should be put into store, as damaged roots are more susceptible todisease. Roots should always be handled carefully to avoid damage and stored as soon aspossible after harvesting. Those that show signs of physical damage, weevil infestation ordisease should not be stored.

5.3.5 Storage struc tures for fresh sweetpotato rootsTwo types of sweetpotato store, the pit and the clamp, are recommended. They have beenshown to work equally well in field trials. Farmers should choose the structure that best suitstheir individual situation e.g. construction materials and local construction expertise that areavailable locally.

5.3.6 Pit sto ragePit stores are holes dug in the ground. The size and shape of the hole is not critical; thequality of the roots selected for storage is more important. Pits should be dug in dry groundaway from areas prone to flooding. The pits are then lined with very dry grass for tworeasons. Firstly, it helps to protect the roots from damage while in the store by acting as acushion. Secondly, it absorbs a certain amount of moisture, stopping the pit from becomingtoo damp and thus preventing the roots from rotting. Sweetpotato roots are placed carefullyinto the pit, which is then sealed with more dry grass and then soil up to normal ground level.This prevents the roots from drying out and stops weevils entering the store. Finally, the pit iscovered with a sloping thatched roof to keep it cool by shading it from the sun, and to preventrain getting into the pit, which could cause rotting. A gap is left between the base of the roofand the ground to allow for ventilation. Locally available materials are recommended to keepcosts down.

5.3.7 Clamp sto rageClamp stores are structures made on a raised flat mound of earth above ground level. Thesize and shape of the clamps are not critical; they depend on the quantity of roots to be storedand local practice. The base of the clamp is covered in dry grass for cushioning and to absorbexcess moisture. Sweetpotato roots are carefully piled on top and then covered with more drygrass and soil to seal the clamp. As with pit storage, this prevents the roots from drying outand the weevils from entering. The mound is then covered with a separate thatched roof toprotect it from the sun and rain, allowing a gap all the way round between the roof and themound for ventilation.

Loading sweetpotato roots carefully into the pit store Shading the pit store with a roof

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Constructing the mound for the clamp store Loading roots carefully into the clamp store

Sealing the clamp store with dry grassand dry soil

Shading the clamp store with a roof

5.3.8 Routine maintenance of pit and clamp storesIt is possible to keep roots in good condition for periods as long as five months during the dryseason. In order to achieve this, it is very important to inspect the stores regularly (every 1 –2weeks) and check for the following potential problems:

• Root rotting• Rodent damage• Insect damage

Root rotting Rodent damage Cylas weevil damage

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If you find any of these problems clear the whole store and discard the affected roots. It is notadvisable to re-store unaffected roots from the same store as they might harbour diseases,but use them quickly to avoid further losses. If the roots are still in good condition reseal thepit or clamp and re-shade it. It is also important to check the soundness of the roof structureand make any repairs at the same time.

5.3.9 Subsequent seasonsPits and clamps can be re-used the following season. Discard all remains of the old grass andsoil covering. Sterilize pits as a precaution especially if you have had any rotting or insectproblems by lighting a fire in them prior to use. Use new dry grass and fresh soil for lining andcovering. If you have encountered problems with mould and rotting try the alternative type ofstore. Also try building the store in a drier position in the next season or altering thedepth/height/size that you build it. Likewise, with insect and rodent pest problems try somealternatives, for example, covering the store with a thicker layer of soil. Some varieties ofsweetpotato store better than others. You may also find that some varieties of sweetpotatokeep better in one type of store than the other.

5.4 Dry storageSweetpotato is mainly consumed as fresh boiled roots. In some parts of East Africa,sweetpotato is traditionally processed into dried chips and flour to preserve the roots forhousehold food security and to a lesser extent for sale in rural markets. Besides permittingbetter preservation, the drying and processing of sweetpotato into dried chips and flour offersother advantages such as:

• facilitating transport and increased shelf life• creating new opportunities for the farmer such as new markets and new sources of

income.

5.4.1 Steps in processing quality dried chips and flourThe steps followed to obtain quality-dried chips and flour are as follows:

• Select only healthy roots for drying• Clean, peel and trim the roots• Wash the roots in clean water. For large scale production a drum washer consisting

of a 200 litre oil drum mounted on a horizontal axle is recommended. The drum canbe cut lengthwise to provide a door that can be opened and closed during loadingand washing of sweetpotato roots, respectively. A handle is fixed on the axle and isrotated during washing. At the end of the drum is an opening for emptying dirty water.The drum can wash 40 kg of sweetpotato roots in 10 minutes using about 30 litres ofwater.

• After washing, pre-dry the roots in the sun for about 10 minutes, then cut the roots

into slices about 5mm thick using a clean sharp knife. For large-scale production amanually operated slicer may be used for this stage.• Soak the slices in clean water for 90 minutes. The recommended volume of water to

be used is twice the weight of slices which is enough to cover all the slices in order toavoid oxidation. In many areas of East Africa the slices are soaked in either saltedwater or in tamarind extract to help protect them against storage pest damage.Salting can also be done after soaking by applying 20-30g of salt per kg of freshlysliced sweetpotato chips.

• After soaking, the slices are either sun dried on a raised tray or in conventional dryersusing firewood or charcoal as fuel sources, depending on suitability of weatherconditions.

• The dried sweetpotato chips are then ready to be milled or ground into flour if that isrequired.

• Sweetpotato flour can be packaged and stored in polythene bags.

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Sun drying of orange fleshed sweetpotatochips on a raised tray for improved quality

Traditional sun drying of sweetpotato chipson ground plastered with cow dung

5.4.2 Storage technologiesTraditional methods of on-farm storage that have evolved over long periods of time are

generally suited to agro-climatic regions and social needs. However there may be a need oropportunity to improve existing storage practices. Features of the most common types ofstorage structures are discussed below.

BasketsClosely woven baskets, or baskets with mudded walls are commonly used for storing driedsweetpotato products. Mudded walls provide protection from rain, strengthen the structure

and prevent uptake of moisture by dry products. Traditional basket stores are built in a widevariety of different shapes and sizes. Baskets often have tight fitting lids and some may haveadditional loading or unloading hatches, which helps to facilitate stock turn-around andmonitoring of the product at the base of the basket. Basket stores can be kept inside thehouse or outside in the open. They should be raised off the ground, placed on stones or brickfoundations or on a wooden platform to prevent uptake of ground moisture. If they are keptoutside they should have a thatched roof or be kept under a shelter to provide protectionagainst rain and shade from the sun.

Mud plastering and sealing woven baskets helps to reduce insect entry, damage by livestockand human theft. Baskets kept inside houses are more secure. Baskets that are well mademay have a life of up to 15 years. Maintenance will include: mending holes or splits in thebasket weaving, repairing cracks in plastered walls and repairing or replacing thatched roofs.

A mudded basket kept outside will need replastering annually. A cement plaster may last forseveral seasons. Before loading baskets should be cleaned thoroughly.

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Solid wall binsSolid wall bins may be round, cylindrical or rectangular in shape. The bins may be made ofclay (sometimes strengthened by mixing with straw or twigs) or from clay blocks or burntbricks. Bins are usually raised off the ground or isolated from it by means of wooden poles,clay pedestals or large stones. Packed earth should not be used as the base because it maypermit termites and rodents to enter the store. Improved solid wall bins made of stones or

bricks and mortar may have a concrete pedestal or foundation. A plastic sheet or tar papermay be used in the base to prevent uptake of moisture.

Some bins have internal dividing walls to make several compartments. This gives someflexibility in the different quantities or products that can be stored. However care must betaken to prevent freshly harvested clean products being placed next to older infested productsas cross infestation can easily occur as insects and rodents move from one food source toanother. Separate openings for filling and emptying are often included at the top and bottomof the storage structure. Covers for these openings can be secured with padlocks.

The life of solid wall bins will depend on construction and local climatic conditions. With goodroutine maintenance and careful use a bin may last for more than 20 years. Solid wall binsare strong and their contents are not displayed to prospective thieves.

The quality of the product stored in solid bin walls may be affected by climate, risk of insectpest infestation and the quality of the design and construction. All bins using mud in theirconstruction are susceptible to termite attack. The area around the bin must be kept cleanand the bin should be thoroughly swept clean at the end of each storage season. Smoke froma small grass fire lit inside the empty bin will kill insects. Cracks in plaster should be repairedquickly.

Metal storage binsIn some areas of Africa, metal storage bins or water tanks made from smooth or corrugatedgalvanised metal sheets are used for storing dried products. They are usually cylindrical in

shape with flat tops and bottoms. There is normally a hatch at the top for loading and a spoutat the side of the base for emptying. Metal bins can provide maximum protection and securitywhen padlocks are fitted to the filling hatch. Metal bins should be placed on platforms or legs

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to allow air to circulate around the base to prevent corrosion from ground moisture. Theyshould be placed under a roof to provide shade and to help reduce moisture migration andheating of the product inside. The cost of bins varies with the size, construction and transportcharges. Although bins can be constructed with different capacities the cost per tonne ofsmall units may be prohibitive. Sweetpotato products are not commonly stored in metal bins,but the adoption of metal storage bins may be something more affluent farmers might be

interested in trying. Adoption of metal storage bins is more likely in those areas where metalcontainers are already used for holding water and they can be made locally by sheet metalworkers.

For storage in metal bins the product must be drier than that stored in traditional bins or bags,this makes the metal bin storage system more suited to areas where the crop is harvested ina distinct dry season followed by storage through a rainy season where good protection isdesirable.

With routine maintenance (including cleaning out residues at the beginning of each season,protecting the structure against corrosion and ensuring that the roof shelter is kept in goodrepair) and careful use, metal grain bins can remain serviceable for more than 20 years.

A well made and well sealed metal bin will provide good protection against insects, mould,rodents and birds. The gas-tightness of metal bins makes them suitable for the use offumigants against insect pests. Baskets and mud walled structures are not suitable forfumigation as the gas escapes through the structure before all the insect stages are killed.Fumigation should only be carried out by specially trained individuals and should never bedone inside a house where people and/or livestock are living.

Bag storageBag storage is a convenient way of keeping dried sweetpotato products. Bags are usuallymade from jute or woven polypropylene, but hemp, sisal, grass and polythene sacks are alsoavailable. Durability of bags will depend on their quality and how they are handled. Jute sacksare more expensive but last longer than woven polypropylene ones. With careful use andrepair bags should last for several seasons. Bags provide the flexibility to store differentproducts and quantities. The storage capacity is limited only by the number of bags availableand the size of the storeroom.

It is important that bags are never placed directly on the floor. They should be stored on smallstorage platforms made from wooden poles. This will allow air to flow under the stacks andwill stop the bags getting wet from uptake of moisture from the ground. If no wood is availablethe bags should be stacked on a plastic sheet. The area around the stack should be keptclear of household items that might provide hiding places for insect and rodents. The stackshould be well constructed to prevent collapse and kept away from the walls of the store ifpossible. In the house the stack should also be kept away from the kitchen and fireplace.

Bag storage is a convenient way of handling and storing dried products. The product can beeasily removed for consumption, inspection or sun-drying, and is immediately available forsale. However bags can also be easily carried away by thieves, but if stored in a house orshed with locked doors and barred windows, they should be fairly secure.

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Successful bag storage depends on adoption of good storage management practice ratherthan construction and operation of a special storage structure. Bags provide little protectionagainst insects, rodents and moisture. Bags should be brushed clean and dipped in boilingwater to kill any insects present at the start of each season. Bags must also be storedcarefully between use to prevent rodents gnawing holes in them. Damage by moisture can beprevented by keeping bags off the floor and by maintaining a sound roof over the stored bags.

5.5 Storage pest and disease management

5.5.1 PreventionTo prevent losses from pests and disease good storage practices must be followed, thismeans:

• making sure that the product is in good condition for storage• keeping the store in good condition• practising good storage hygiene

Making sure that the product is i n good condi tion for s torageGood quality dried sweetpotato products are less likely to suffer insect attack than poorquality products. Before storage carefully inspect the product for insects and any signs ofdisease. If some of the product is infested, make sure this infested portion is used first and donot store it in contact with the good quality product as it will lead to cross infestation. If insectsare present, winnow the product to remove them and then sweep the insects up and burnthem. Winnowing will only remove the adult insects, and although some of the developingeggs and larvae may be killed during sun-drying others may still be developing inside theproduct. Remove any straw, dirt, weed seed, stones or other foreign matter from the productas these materials will hold water and a damp product will become mouldy.

Keeping the store in good condi tion A good store should keep the product cool and dry. It should also protect it from rodents,birds, farm animals and thieves. Most stores (except some solid wall stores that can besealed) do not prevent insects entering.

The store should be built in a well-drained location, away from branches of trees otherwiserats may jump from the branches onto the store. The store should be kept under a roof thatkeeps the rainwater out and provides shade. The store should be raised off the ground toprevent water soaking into it and to prevent rodents and farm animals reaching the storedproduct. If wooden posts are used to raise the storage structure, they may need to beprotected against termite attack, used car-oil is often applied for this purpose or the centralparts of mopane trunks (or other tree species) which are resistant to termite attack can beused.

Rat guards should be fixed to the legs of the store to stop rats from climbing into the store.Rat guards will only work if the store is raised at least 1 m off the ground and there are noplants or poles close to the store up which the rats and mice can climb. The store should bebuilt at least 1m away from buildings and trees. Cats and dogs help to frighten rats away. Ifthe product is stored in a storeroom or house, traps can be used to help catch rats. Rodentsusually move around the base of the walls of a room so traps should be placed on the floor bythe walls or in the corners. Rodents can transmit many human diseases and should not behandled with bare hands if possible, dead rodents should be buried in pits to reduce the riskof disease transmission. As rodents are mammals (like humans), poisons that are sold to killthem are also highly toxic to humans. It is therefore very dangerous to use rodent poisonsnear food and in areas where children and livestock might interfere with them. Rodentpoisons should only be used by people who are specially trained in rodent control.

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Examples of home made rat guards

Practisi ng good storage hygieneThe storage site and the area around it must be kept clean and free of breeding sites forpests. Rats and mice will breed in rubbish heaps. Insects will breed in old stocks ofsweetpotato, cassava and grains. All residues from previous harvests should be removedfrom and around the store and burnt. If the product is to be stored in containers, these mustalso be cleaned, sacks should be turned inside out and brushed to remove crop residues, thesacks can then be dipped in boiling water to kill any insects present and then dried in the sun.

Any holes should be repaired. If the storage structure has mud walls these should be re-plastered each season to destroy any insects or disease spores remaining from the previousseasons in the cracks. Insects that hide in the timbers, basketwork or thatch of stores aredifficult to kill and can lead to rapid infestation of the new crop. Empty stores can be treatedwith pesticides to reduce insect infestations. However the Larger Grain Borer (LGB)Prostephanus truncatus (see section 5.5.4) can bore deep into timber, and if the store hasbeen infested by LGB in the previous season, the risk of damage to the new crop may bereduced by changing any wood that shows signs of LGB damage. The discarded woodshould be burnt quickly, and not kept as firewood otherwise LGB may come out of the timberand infest the newly stored product and other structures.

5.5.2 MonitoringTo make sure that the crop and the store remain in good condition throughout the season thestore and the stored product must be inspected regularly for signs of damage by birds, mice,rats, and insects. Signs of insect damage can include: small feeding holes in the product;large amounts of dust in the product, sacks or storage structure; presence of insects; anddistinctive smells. If signs of pest attack are spotted early, action can be taken before thedamage becomes too severe.

5.5.3 Management of storage insect pests in dried sweetpotatoTo date surveys have found that in East Africa the main insect pests of dried sweetpotatoproducts are similar to those of dried cassava products. These dried products suffer damagefrom a wide range of stored product insect pests, the adult stage of many of them are shownin the diagrams below. Stored product pests tend to be small, usually less than 1 cm inlength. As with field insect pests, the adult stages often bore holes and lay the eggs and thenthe developing larvae feed inside the dried product producing feeding tunnels in the product,which can reduce both the quality and quantity of the product. Pupation usually occurs withinthe product and the adult insects then emerge, mate and lay the next generation of eggswithin the product. During feeding the insects often cause a lot of dust to be produced, alongwith the appearance of holes in the product the dust acts as a sign that insects are infestingthe stored product and action should be taken.

Many of the traditional processing practices used for dry storage of sweetpotato products canhelp reduce insect damage during storage, several of the practices which can be integratedwith each other are discussed:

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Harvesting and Post Harvest Practises

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