Tidskrift/serie: Examensarbeten - Sveriges lantbruksuniversitet, Institutionen för växt- och skogsskydd
Utgivare: SLU, Institutionen för växt- och skogsskydd
Författare: Päts P.
Titel: A survey on maize and potato storage in Kenya, with particular reference to post-harvest losses caused by insects
Nummer (ISBN, ISSN): ISSN 0348-5625
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Detta arbete genomfördes i samarbete med ett FAO/SIDA projekt i Kenya gällande små lagerhus lämpade för gårdslagring. En tidigarelagd skörd är möjlig med dessa lagerhus då de även möjliggör torkning av majs med hög vattenhalt.
Förutom en beskrivning av FAO/SIDA's projekt beskrivs alla andra projekt, institutioner, myndigheter och den pågående forskningen som berör lagringsproblematiken.
Skadegörare på lagrade produkter är ett stort problem i de flesta utvecklingsländer. Att uppskatta förlusternas storlek är svårt. Källor nämner förluster i storleksordningen mellan 4 och 40% efter 12 månaders lagring.
Majs är en basföda i Kenya och odlas av i stort sett alla småbrukare. Karaktäriserande för Kenyas jordbruk är det stora antalet småbrukare. 59% av alla jordbruk är mindre än 2 ha och endast 3% överstiger en storlek på 8 ha. Detta beror mycket på den stora befolkningstillväxten som för närvarande är 4% årligen. Potatis är en gröda som börjar odlas mer och mer.
Bekämpning av förrådsskadedjuren är föga omfattande. Den förekommande bekämpningen baseras i stort på kemiska medel. Det rapporteras att insekticider som DDT, aldrin och klordan har använts och kanske används för detta ändamål, vilket de ej är registrerade för.
Efter en genomgång av de viktigare skadeinsekterna på lagrad majs och potatis, lägger författaren fram olika förslag på fortsatt arbete för att minska lagringsförlusterna och användandet av insekticider. Bland annat nämns feromoner, patogener (Bacillus thuringiensis), tidigarelagd skörd och integrerad bekämpning. Det senare är utarbetat i Peru för bekämpning av potatismalen (Phthorimaea operculella).
Arbetet avslutas med en lista på de publikationer som rör de arbeten som genomförts angående lagringsproblematiken i Kenya.
The field work for the present report was undertaken as a part of a Minor Research Task (MRT) conducted in Kenya during February and March 1984.
The MRT, a SIDA financed activity, is a smaller study or research project that should not take longer than three months to complete. Two of these three months are expected to include field work in the receiving country. The purpose of this report was to review today's knowledge concerning storage and stored product protection in Kenya. The review was made on behalf of the Swedish University of Agricultural Sciences, Department of Plant and Forest Protection. It is to function as an introduction and aid for people who intend working with crop storage in Kenya.
Before the field studies were carried out, I conducted a literature survey to familiarise myself with control strategies used against insects attacking stored products. Relevant literature was located with the help of a computer, and is partly quoted in this report. The actual field studies in Kenya were conducted to investigate present and planned research, and to find out which control methods are applicable.
The task was carried out in cooperation with current Swedish aid performed by FAO/SIDA Cooperation Programme, Rural Structures.
Uppsala, April 1985
I am very grateful to all those who have helped me in any way to make this report possible. Besides my thanks to all persons visited, I particularly want to thank SIDA who sponsored the MRT, and the Kenyan farmers involved for the help and hospitality.
Special thanks are also due to all the staff of FAO's Regional Office, Rural Structures in Nairobi, who helped me in every way, and my two supervisors, Mr. Leif Eriksson and Professor Jan Pettersson.
Mr. Leif Eriksson is a Farm Building Engineer working as an Associate Expert for PAO/SIDA Cooperative Programme, Rural Structures in Kenya.
Dr. Jan Pettersson is professor at the Research and Training Division of Entomology, Department of Plant and Forest Protection at the Swedish University of Agricultural Sciences in Uppsala, Sweden.
CIP - Centro International de la Papa (International Potato Centre)
DPRA - Development Planning and Research Associates, Inc.
FAO - Food and Agriculture Organization of the United Nations
GAT - German Agricultural Team in Kenya
GTZ - Deutsche Gesellschaft für Technische Zusammen- arbeit (German Agency for Technichal Cooperation)
ICIPE - The International Centre of Insect Physiology and Ecology
MOALD - Ministry of Agriculture and Livestock Development
MRT - Minor Research Task
NAL - National Agricultural Laboratories
NCPB - National Cereals and Produce Board
RSU - Rural Structures Unit
SIDA - Swedish International Development Authority
USAID - United States Agency for International Development
16,50 KSh = US$ 1,00
1,76 KSh = SEK 1,00
1 bag = 90 kg
From the time that man settled down and started with agriculture, storage of foodstuff s and seeds has been a natural and integral part of his strategy for survival. Food has to be stored from one growing season to the next, and a reserve has to be kept in the case of a bad harvest. Stored foodstuffs are a concentrated source of nutrition for various organisms such as insects, acari, rodents and fungi which can cause both quantitative and qualitative losses. The kinds of organisms causing serious losses vary seasonally, mostly due to climatic factors. There is, however, general agreement that insects are, by far, the most important of the biological agents responsible for postharvest losses. Table 1 shows estimations of average post-harvest losses.
Table 1. Estimated average post-harvest losses of cereal grains
|Area||Average loss, %||Storage time||Cause||Source|
|The world||10%||12 months||insects, mould||Prevett,1975|
|Zambia||2-6%||12 months||insects||Adams, 1977|
|Malawi||1-2% (sorghum)||6-10 months||insects||Golob, 1981|
|Kenya||4,5%||12 months||insects||De Lima, 1979|
|10%||12 months||insects, mould||DPRA, 1980|
|40%||12 months||all||Anon., 1984|
The importance of saving the harvested crop is well illustrated by the following example. Every percent of harvested maize saved is equivalent to 23 400 tons in Kenya alone, which is food for about 180 000 people for one year.
Its importance is amplified when one takes into account Kenya's 4% annual population increase.
Maize is the most important food crop in Kenya. About 70 - 80% of the total maize production is kept on the farm for home consumption. Potatoes (Solanum tuberosum) are a smaller crop but are increasing in popularity. Since potato marketing is free, it is important for the farmer to be able to store potato tubers for up to several months in order to even out the market supply and reduce price fluctuations. About 70-80% of the potatoes are not marketed and therefore kept on the farm. The lack of suitable potato storage facilities leads to considerable losses.
Kenya is an equatorial country with extreme variations in altitude and climate.
About 12% of Kenya's land is considered arable, i.e. land which receives an average of 857.5 mm rain or more annually. In most of the eastern two-thirds of the country, there are two rain periods a year. One in April-May termed "long rains" and one in October-December termed "short rains". Farther west in the Highlands there is only one rainy season. Over half the annual precipitation occurs between April and June along the coast. Around Lake Victoria there is a large area with a rainfall of 1250 mm of more fairly evenly distributed throughout the year. In the areas with distinct rainy seasons, rainfall is not considered to be very reliable.
Altitude and soil quality are also primary determinants of land use in Kenya. Low temperatures limit cultivation at about 2750 m above sea level. Crops such as potatoes, wheat, coffee and tea can only be grown at altitudes above ca. 1800 m. Coconut trees and tropical fruits can only be grown along the humid and warm coastal area.
Soil types range from Laterites to Lithosols and desert soils. The Laterite soils are among the most productive soils in Kenya and occur on the level and undulating areas of the highlands. Lithosols and desert soils have no agricultural value in Kenya except for some grazing.
About 80% of Kenya's population of 19 million people are agricultural. Smallholders are the predominate source of food, including the marketed produce. Not less than 59% of the holdings are of less than two hectares (Table 2).
Table 2. Distribution of holdings by size
Size of holding
|0,5 - 0,9||267||18|
|1,0 - 1,9||400||27|
|2,0 - 2,9||222||15|
|3,0 - 3,9||133||9|
|4,0 - 4,9||104||7|
|5,9 - 7,9||104||7|
Source: CBS. 1977,
Cash crops such as coffee and tea are not grown over a large area but are Kenya's greatest source of export income. Sorghum and millet were the basic food crop in Kenya before Europeans introduced maize. Maize and beans are now the most important food crops in Kenya. The former is a staple food and the average consumption is about 131 kg per person and year (FAO 1983b). Figure 1 shows the amount of area used for cultivating some of Kenya's most important crops.
Figure 1. Most common crops grown in Kenya (FAO, 1983b)
Maize is harvested once a year in some areas and throughout the year in others. Average yield varies from 0.7 tons per hectare in the lower parts of Eastern Province to 4.1 tons per hectare in the higher parts of Nyanza and the Western Provinces. The national average yield is 1.2 tons per hectare (FAO 1983b).
Potato (Solanum tuberosum) is a crop grown at altitudes higher than 1800 m above sea level and can be to harvested twice a year. The average yield is 6.5 tons per hectare which gives an average consumption of 14,6 kg of potatoes per person and year (FAO 1983b). The distribution and marketing of potatoes is controlled by the farmers themselves and by various organisations. There is no state controlled marketing board for potatoes.
The traditional method of maize storage is to leave the maize in the field until the moisture content is reduced to about 18%. Further reduction of the moisture content is achieved by "stocking" in the field or drying on the cobs on the ground if harvested directly.
Maize is then stored on cobs in granaries with or without husks, depending on traditions. Some hang the cobs on racks inside dwellings or in trees.
The granaries or cribs vary in size and configuration from area to area. The most abundant storage structures are circular woven basket types, sometimes plastered with mud or cowdung, and rectangular cribs made of split wood poles, sisal stems etc.
Figure 2. Different types of traditional storage structures (photo, author)
Some insect species attack cereals in the field prior to storage, e.g. the maize weevil (Sitophilus zeamais), the rice weevil (S. oryzae) and the angoumois grain moth (Sitotroga cerealella). These insects are then carried into the store in connection with harvest. Cereals left from one storage season to the next and poorly cleaned storage structures are other very serious sources of insect infestation.
Insect control is traditionally not very common. In some areas, however, ashes are mixed with shelled grain or the cobs are smoked with or without husks in attempts to control pests. It has also been reported (DPRA 1980) that fresh, wild marigold (Tagetes minuta) is sometimes put in cribs as an insect repellant, though this was never observed by the author.
Ashes have been proven effective in high concentrations. 30% ashes by weight are required to give the level of protection against insect attack equivalent to the recommended dose of Actellic dust, 40 g of 2% pirimiphos-methyl to 90 kg maize in Malawi (Golob et a1. 1982). Smoking has not been proven effective in reducing insect attack.
Chemical protection is not widely practised at present.
About 40% of the farmers treat their maize with a protectant, including ash. 57% of these individuals did not know what they had used (DPRA 1980). Insecticides such as DDT, aldrin and chlordane have not been approved for protecting grain used for human consumption, but they are reportedly being used.
All maize (and wheat) that is not to be stored for consumption by farmers and their families has to be sold to the National Cereals and Produce Board. NCPB is a parastatal organisation whose main purpose is to buy, store and distribute cereals, and has exclusive permission to handle maize and wheat.
The latter is mainly grown by large-scale farmers, whose produce is transported, directly after harvest, to large silos located in Eldoret, Kitale and Nakuru. Maize, on the other hand, is mainly grown by small-scale farmers who have difficulties with transportation. Excess maize is therefore sold to the NCPB at buying centres usually located within a short distance from the small-scale farming areas.
The storage capacity at the buying centres is about 5000 bags. Before transport to depots, insecticides are admixed to maize if it is expected to be stored for a longer period of time (maximum 120 days). Conversely, if maize is in short supply and is going to be transported to the depot quickly, it is left untreated.
There are around 40 depots in Kenya and bagged maize is stacked in large stores, each with an approximate capacity of 100 000 bags. The stacks are then covered with tarpaulins and fumigated with methyl-bromide.
Some maize and wheat is kept for long-term storage as a strategical reserve for famine relief in so called "Cyprus Bins". The bins, 40 at Kitale and 30 at Nakuru, were constructed in 1967-68. They have a total storage capacity of about one million bags of grain (90 000 tons).
The Cyprus Bins are sufficiently air-tight to enable long-term storage of grain without the use of insecticides or fumigants. Losses are small and have been estimated to be only one percent after 3 years storage (Baker, 1974).
The NCPB lack stores during years of good harvest. It is of great importance to be able to store grain for about 3 years in order to be independent of fluctuations in yield.
One cheap way of improving the national storage capacity is to improve the on-farm storage capacity. During years with exceptionally high yields, the NCPB cannot accept all maize that the farmers want to sell, and poor on-farm storage methods undoubtedly lead to high losses.
Rural structures are defined as structures for the storage and processing of crops, and structures for sheltering domestic animals (SIDA, 1983).
The countries involved in the Rural Structures Programme are Kenya, Zambia, Lesotho, Malawi, Swaziland and Tanzania. The work is coordinated by a Regional Coordinator based in Nairobi, Kenya.
The objective of the project is to provide assistance to the participating countries in the development and extension of low cost, rural structures. The project is aimed at small-scale farmers since about 70-80% of the population in the region live on farms smaller than 8.0 hectares. Besides storage structures for maize and potatoes, structures for water tanks, chicken houses and zero-grazing units are evaluated by the project. Special training courses for young officers from the participating countries have also been conducted in order to assist the respective ministries in developing the necessary local expertise.
The participating countries have also established specific Rural Structures Units with the objective of developing national expertise in the field of rural structures. The Rural Structures Unit in Kenya is located within the Ministry of Agriculture and Livestock Development, Land Development Division.
FAO's interim report for 1983 gives full information on phase I of the project. Phase II started on January 1, 1984 and is to continue for 3 years.
This unit was established in early 1979 to service the relevant ministries and divisions in the field of rural structures. The unit provides assistance in the development and extension of functional, low cost structures, utilizing locally availale materials and skills. The unit, which is located in Nakuru, is staffed with eight Technical Officers and two Technical Assistants. A FAO Associate Expert is provided for technical in-service training. The operational costs for the unit have been exclusively sponsored by the Swedish Government through the FAO/SIDA Cooperative Programme.
From 1979 to the end of 1981, a series of development and test programmes concerning different harvesting, drying and storage systems were carried out at five different locations with different climatic conditions. The main result from this work was the development of a grain drying and storage crib (see Figure 3) for small-scale farmers as well as the development of appropriate methods of grain handling.
Figure 3. The improved maize crib (from RSU, 1984a)
About 300 cribs have been erected in Central, Eastern and in the Rift Valley Provinces. Most cribs are located at Farmers Training Centres and at certain leading farms for demonstration purposes and further monitoring work. The maize crib is made of locally available materials; the roof can either be of thatch or corrugated iron sheets. Although corrugated iron is more expensive, a thatch roof can be difficult to make due to lack of grass and skilled labour. The "standard" size for a crib is 3.20 m long and 1.50 m wide. The length can vary, depending upon the storage capacity which the farmer wishes to have. The width should not exceed 1,50 m since it prolongs drying time. This crib can hold about 20 bags of shelled maize, equivalent to 34-40 bags of cob maize. Using this crib it is now possible to harvest at 25-30% w.c., that is 3-4 weeks earlier than traditional harvest time (17-18% w.c.). It is also rat-proof. Up to 50% of the wall area consist of openings that allow air to pass through quite freely. It takes an average of 45 days of drying before the maize reaches 13% w.c. and is then safe for storage.
Harvesting at maturity, i.e. about 30% w.c., has many advantages. The fact that the crop leaves the field 3-4 weeks earlier means:
The Rural Structures Unit gives the following recommendations for post-maturity handling.
These recommendations are similar to those by DPRA (1980), which estimated that losses were reduced to 4,6% from 16.9% when this harvest and drying method was used in place of traditional methods. The pre-harvest losses were reduced from 6,1% to 2.0% and insecticide treatment saved 2,2% of the grain. Losses due to mould were reduced by almost 6%. These latter figures refer to 12 months of storage. Shelling and bagging enables the even application of insecticides, requires less storage space and facilitates inspection of the produce during storage. A lower cost alternative to the crib is a raised platform (Figure 4).
Figure 4. Raised platform for drying (from Owende, 1984).
This platform also allows early harvest, and is suitable for farmers who cannot afford a large investment. The platform is more labour intensive and must be protected from rain but provides very fast drying (Jacobsson, 1983 and Owende, 1984). See Figure 5.
Figure 5. A comparison of the number of times it is possible to dry maize down to 13% w.c. on a platform within the same time it takes the maize to reach 13% w.c. in a 1.5 m wide crib (after Pepke, 1981).
A separate storage structure is necessary when using a platform. An improved "FAO" crib, however, is intended for both drying and storage.
The platform can also be used for other purposes, e.g. for drying coffee beans and pyrethrum flowers. RSU wants to start trials in cooperation with the Pyrethrum Bureau to examine the suitability of these platforms for drying pyrethrum flowers.
Besides the work on maize drying and storage structures for smallholder farmers, the RSU has been assisting work with ferrocement stores (made of reinforced steel, chicken wire and covered with cement mortar, also described on page 25) suitable for cooperative societies at village level.
RSU has also, in cooperation with the crop storage engineer within MOALD's Crop Protection Branch, carried out trails on potato storage. A special ware potato storage structure is now in the RSU's programme to provide the farmers with storage recommendations and help with construction work. Another part of RSU's work is to train local craftsmen and advisory personnel in the construction of stores and in the handling and storage of maize and potatoes, respectively.
Water tanks and zero-grazing units for demonstration purposes have also been built by RSU together with FAO/SIDA Re- gional Offices.
The function of this Division is to promote agricultural crop production in the country in collaboration with other related agencies. The Division achieves this by providing technical and policy guidelines on horticultural, industrial and food crops as well as post-harvest management of crops. There are four branches in the division:
The Crop Storage Engineer is the ministries representative in storage and has three main tasks. These are to (a) coordinate the storage work between different branches within the division, (b) train extension staff at the districts and (c) develop storage structures and storage methodologies. Examples of above-mentioned tasks are the evaluation and construction of potato stores. A handbook on Potato Storage has also been written. The potato storage work has continued in cooperation with the Rural Structures Unit, funded by FAO/SIDA.
Post-harvest technology for maize has been evaluated together with the Rural Structures Unit. Courses have been held in potato, grain and vegetable post-harvest technology. Inspection of constructed storage buildings is also carried out.
This branch, with staff in four provinces and 14 districts, has the following tasks:
The branch is divided into four units according to the pests that are to be controlled:
Birds and armyworms have been omitted here since they are beyond the scope of this report.
The rodents of interest for The Crop Protection Branch are:
Of the above-mentioned rodents, the multimammate rat and the striped rat are also pests in small-farm grain stores. The black rat (Rattus rattus) and brown rat (Rattus norvegicus) are the more serious rodent pests at large central stores.
The unit monitors outbreaks of rodents, which follow an approximate 7-year cycle. The cycle depends on rain, and the rats usually cause problems during the dry years following wet years. Baiting campaigns with Zinkphosphine are executed when necessary, i.e. about every seventh year.
This is a specific unit which serves the farmers with storage recommendations evaluated by the National Agricultural Laboratories. A large part of the service is extension work. It is this unit that is also responsible for the recommendations and supply of insecticides for the control of the greater grain borer (Prostephanus truncatus) in the Taveta region. This unit will probably be the Kenyan Government's representative in the GTZ's Greater Grain Borer Project that will be set up during 1985.
The unit is the Kenyan Government's representative in the DPRI "On Farm Grain Storage Project" in Maseno which is sponsored by MOALD/USAID (described on page 28).
No research is undertaken by Crop Protection Branch. The recommendations given by the branch and the control measures conducted by them are based on results gained from other organisations.
Crop storage work at NAL began before the second World War. Its main objective is to provide technical services and undertake research in the fields of agricultural chemistry, agricultural entomology, plant pathology and soils. NAL has functioned as a coordinator for storage research in Kenya. The work that has been carried out has dealt with both large and small holder farmers. A summary of NAL's Crop Storage Research Programme is presented below.
Besides the ongoing research there are a number of proposals for further work. NAL plans to do post-harvest loss assessments in "lesser" stored cereals and, if losses are considerable, evaluate control and storage methods for these grains together with studies of insect-caused food and storage losses in beans and other pulses. Storage losses and their control in dried and smoked fish is another subject not extensively studied but suggested for future studies. Except for the studies on the use of edible oils for the control of bruchid beetles most of the research is concentrated on studies of insecticide control methods. There are, however, proposals for research on alternative control methods such as the use of inert materials (e.g. woodcuts and diatomite dust) in the control of storage pests, and the possible usefulness of neem tree (Azadiracta indica) leaves and fruits against various storage pests.
An investigation of varietal resistance and susceptibility of Kenyan maize to insect attack is likely to be conducted in the future.
A comparative evaluation between traditional and improved storage structures in terms of drying efficiency and storage ability under various agroclimatic zones in Kenya is also in the program for coming work.
The National Agricultural Research Station in Kitale screens insecticides for use against storage pests.
The National Plant Breeding Station in Njoro conducts research with Triticale and is trying to improve its storage facilities since it is very susceptible to storage pests.
The National Dryland Farming Research Station in Katumani screens cowpea and pigeonpea for resistance to bruchids.
The National Coast Agricultural Research Station in Mtwapa tests new storage structures. The station also estimates the level of field infestation, especially of maize, at the time of harvest.
Pyrethrum is a cash crop grown in the highlands of Kenya and was first introduced in 1931 (Acland, 1971). Kenya is the world's largest producer of pyrethrum and accounts for 95% of the world's production.
Pyrethrins are natural insecticides prepared from the flowers of the pyrethrum plant (Chrysanthemum cinerariaefolium) and contain six distinct but related insecticidal ingredients.
The Pyrethrum Board of Kenya is a partially state-run organisation with its headquarters in Nakuru. The Pyrethrum Board is responsible for regulating the quantity of pyrethrum flowers produced each year and for developing measures for improving the quality and efficiency of production. The Pyrethrum Board also undertakes the processing, sales and marketing of pyrethrins and its by-products. The actual research concerning breeding, vegetative propagation, pest and disease control, and advisory services to farmers are conducted by the National Agricultural Research Station in Molo.
The Pyrethrum Bureau is the technical service organisation attached to the Pyrethrum Board. The Bureau provides advice and information on the formulation of pyrethrin-based insecticides. To give advice on formulation the Bureau has had to carry out extensive research on a wide variety of insecticides.
The present research conducted by the Bureau includes the above-mentioned comparisons of different insecticides, application of pyrethrins to stored foodstuffs, and also, application of pyrethrins to field crops and reevaluation of the LD50-value (in cooperation with the University of Nairobi).
Future research projects include more extensive dose/mortality bioassays to find out if it is worthwhile spraying pyrethrins on cereals while loading them into central storage areas, e.g., silos. At present, either methyl-bromide or malathion is used.
An extensive stock of various insect species is kept in culture for the insecticidal research. See Table 3.
Table 3. Stored product insect stock cultures in Kenya
|Species||Pyrethrum||National Agricultural Laboratories|
Source: Personal communication from Pyrethrum Bureau and NAL.
Information about the research concerning pyrethrum in Kenya as well as in other countries is published in the Pyrethrum Post, the official publication of the Pyrethrum Board. The Pyrethrum Post, with four publications annually, is distributed free of charge to users of pyrethrum and to scientific and educational organisations.
The recommended dose of pyrethrins for stored products is 3 ppm, i.e. 125 g, 0.2% dust to 90 kg of, for example, maize. Pyrethrins are the only approved insecticides for admixture in many industrial countries, e.g. USA and Australia. The high cost of pyrethrin applications is one of the most serious disadvantages of the chemical, see Table 4.
If the use of pyrethrins as a storage insecticide is to increase in Kenya and replace organic phosphorous compounds, the price must be lowered. For the moment, the manufacturing cost of pyrethrum dust is 9.70 KSh/kg. However, the consumer must pay 41.75 KSh for the same amount of pyrethrum.
Table 4. A comparison between approved insecticides for admixture in grain and other foodstuffs
Cost per treated
|Pirimiphos-methyl||1% dust||50 g (5ppm)||12.35/400g||1,54|
|Bromophos||2% dust||50g (10ppm)||5,20/200g||1,30|
|Malathion||2% dust||50g (10 ppm)||7,25/400g||0,90|
|0,2% dust||125g (3 ppm)||8,35/200g||5,22|
*) DDT not approved for admixing in foodstuff but reported being used.
Source: Pyrethrum Bureau, 1985 and author.
This department has carried out research concerning the technical aspects of storage.
Trials with various storage containers for maize (improved maize crib) and potatoes (ware potato store) have been conducted to study the effects of container width and wall openings on drying rate. In 1983 this department and the De- partment of Farm Buildings at the Swedish University of Agricultural Sciences cooperated in the construction of two socalled "ferrocement" stores (Nilsson, 1982 ; Påhlstorp and Henriksson, 1984).
These stores (see Figure 6) have been placed at the University's Kabete campus.
Figure 6. The ferrocement store (from Nilsson, 1982).
The storage facility is constructed of a reinforced steel frame and three layers of chicken wire covered with cement, and can store about 250 bags. If made larger, with a capacity of 2500-3000 bags, it might be suitable for buying centres. Unfortunately, since there was a shortage of maize in 1984, a full-scale storage trial has been postponed indefinately. The trial was meant to test the general storage capability of the facility and to determine the ease with which it can be effectively fumigated.
At the time of this writing, no storage research is being carried out at the University of Nairobi. However, there is a proposal for further research that includes a comparison between early harvested maize and artificial drying versus late harvest and field drying, in terms of losses. Additionally, comparisons of various harvest systems and dryingstorage structures have been proposed. Forthcoming research will also attempt to evaluate the use of artificial drying in large scale farming.
The department has had problems with the continuity of its research programs since many of its staff have moved on for further education; some of them have studied abroad for long periods.
GAT is the working name for the agricultural projects carried out in Kenya by GTZ.
GAT has not been involved in specific post-harvest research and development since its involvement with potato storage in 1977. However, it is now setting up a project to study the greater grain borer, Prostephanus truncatus (Coleoptera; Bostrichidae).
P. truncatus is a new stored products pest in Tanzania and Kenya. It was first found in Tanzania in 1980 and is spreading rapidly. It is now established in the Taveta region in Kenya. In the Tabora region in Tanzania the normal losses due to insects did not exceed 1-2 percent after 6 months storage. However, P. truncatus presently causes an average of 9% weight loss in maize and some losses exceeding 30% after 3-6 months storage (Golob, 1983). What makes P. truncatus so serious a pest is its ability to develop rapidly on cob maize which is commonly stored in East Africa and its ability to develop in very dry grain (less than 10% w.c.). Moreover, the presence of P. truncatus leads to increased infestation by Tribolium spp., no natural enemies have yet been recognised in East Africa, and the beetle can damage various roots and tubers, cereals, pulses, cocoa, coffee beans, groundnuts, wooden structures and utensils. P. truncatus requires maize, soft wheat or dried cassava to be able to reproduce rapidly.
P. truncatus does not develop as well in shelled maize as it does on cob maize (Hodges, 1982). Hodges also recommended shelling, since it allows more effective treatment of the grains. Presently, 2.5 ppm permethrin (0.5% applied at 50 g per 90 kg bag of maize) is recommended for admixing to control P. truncatus. If permethrin is not available, Actellic dust (1% pirimiphos-methyl) should be applied at the same rate although it is less effective. Pre-harvest infestation is apparently high (Hodges et a1, 1983); thus, an earlier harvest should lower post-harvest losses. Shelling, itself, lowers the developmental rate of P. truncatus while also making insecticide admixing more efficient.
If P. truncatus spreads all over Kenya, then FAO/SIDA's and RSU's general recommendations for maize storage (early harvest, shelling, chemical treatment) also apply for the control of P. truncatus.
The GAT project that is planned to start May 1, 1985 and continue to April 30, 1989 has the following objectives:
The DPRA, a private US Consulting Firm, carries out an "On Farm Grain Storage Project". The project is sponsored by MOALD and USAID. USAID and a section within MOALD will support and coordinate the activities aimed at reducing smallholder grain losses.
The project resulted from the Kenya National Crop Storage Study that DPRA prepared for USAID in 1980. It was estimated in the study that total post-maturity (except handling) maize losses exceeded 16%. Of the losses, about 6% occurred between maturity and harvest and 10% between harvest and time of consumption (12-months storage). The report recommends harvesting maize at physiological maturity (about 30% w.c.) to reduce field losses and pre-harvest infestation.
That means harvesting about 4-8 weeks earlier than usual. The cobs should be dried down to about 13% w.c., which is a safe storage moisture content, on platforms or in ventilated cribs. The maize to be stored for a period of more than 3 months should then be shelled and treated with an insecticide.
The project started in 1984 with its centre in Maseno, Western Kenya, where a laboratory was set up. Extension staff are also located at Kakamega. Besides the reserach carried out at the station in Maseno, a number of grants for M.Sc. studies in the USA are also included in the project. These M.Sc. students will act as counterparts and will later replace the international staff.
The extension staff collect stored maize samples from farmers using different storage methods. Insect and mould damage are then evaluated in the laboratory.
In the future, research will be expanded to include other crops such as beans and sorghum. Further investigations of pre-harvest losses and loss assessments may also be conducted.
|Species:||Sitophilus zeamais||Maize weevil (Eng.)|
|Sitophilus oryzae||Rice weevil (Eng.)|
Figure 7. A. Adult Sitophilus oryzae (from Freeman, 1960). B and C. Y-shaped 8th sternum from female S. oryzae (B) and from S. zemais (C). D and E. male copulation organs from S. oryzae (D) and S. zemais (E) (from Weidner, 1982).
Adults 2.5-4.5 mm long. The snout is welldefined. Antenna elbowed and clubbed. Punctures on prothorax round and very dense. Elytra usually with four reddish spots. S. oryzae, in general, smaller than S. zeamais. Separation of the two species can be achieved with certainty by examination of the genitalia (Kuschel, 1961; Halstead, 1964). However, it has been reported, that there are also reliable external characters that make it possible to distinguish between the two species (Boudreaux, 1969).
S. zeamais: Maize. Sorghum, rice and other cereals are alternative hosts. S. oryzae: Rice. Maize and other cereals are alternative hosts.
Primary pests hollowing out grain. Both adult and larvae cause feeding damage.
The female chews a minute hole in the grain where a white, oval egg is deposited. The hole is then sealed with a gelatinous secretion. The apodous larva remains inside the grain where it feeds and eventually pupates. The adult bites its way out of the grain when development is complete. Each female is capable of laying 300-400 eggs. The adults can live for up to 5 months. The weevils are capable fliers, but flight activity is more pronounced in S. zeamais. Pre-harvest infestation occurs. The life cycle is about 40 days at 30°C and 70% r.h. S. oryzae is more common on small cereal grains and has a higher temperature tolerance than S. zeamais.
Longstaff, B.C. 1981. Biology of the grain pest species of the genus Sitophilus (Coleoptera; Curculionidae): A critical review. Prot. Ecol.,2, 83-130.
|Species:||Tribolium castaneum||Rust red flour beetle (Eng.)|
|Kastanjebrun mjölbagge (Swe.)|
|Tribolium confusum||Confused flour beetle (Eng.)|
Figure 8. A. Adult Tribolium castaneum and B. T. confusum. C. Head from T. castaneum (above) and T. confusum (below). D. Shows antennae from T. castaneum (lett) and T. confusum (right). E. Tribolium larvae (A, B from Hallas & Mourier, 1984; C-E from Weidner, 1982).
Flat, 3-4 nun long beetles with elongate, reddish-brown bodies. T. castaneum: antennae with distinctly three-segmented club. T. confusum: antennae gradually thickened towards apex.
Maize, wheat and other stored grain and milled cereal products.
A serious secondary pest throughout the warmer parts of the world in food stores. Preference shown for the embryo of cereal grains.
Each female is capable of laying 400-500 eggs. The small, cylindrical eggs are laid in a scattered fashion directly in the produce. The larvae are yellowish-white, cylindrical and about 6mm long when fully grown. Pupation takes place in the food and emerged adults can live for more than one year. Both adults and larvae cause feeding damage. The time from egg to adult is about 20 days under optimal conditions, but the developmental time is markedly affected by the quality of their food source. Optimal temperature is about 35°C for T. castaneum and 33°C for T. confusum. Optimal r.h. is 70%.
|Species:||Rhizopertha dominica||Lesser grain borer (Eng.)|
|Prostephanus truncatus||Greater grain borer (Eng.)|
Figure 9. A. Rhizopertha dominica (from Freeman, 1980) and B. Prostephanus truncatus and its antennae (C) (from Lepesme, 1944). D. Dorsal view of R. dominica and E. P. stephanus. F. Posterior view of P. truncatus. Arrows indicate the pronounced lateral ridges. (D-F from Hodges, 1982).
About 3-4 mm long beetles, P. truncatus often slightly larger. Body browndark brown and cylindrical in shape. Head not visible from above. Antennae 10 segmented with a large, loose three-segmented club. P. truncatus is distinguished from R. dominica by its elytra which are flattened posteriorly and incline quite steeply, and by its sloping region which has two pronounced lateral ridges.
R. dominica: Stored cereals. Other foodstuffs, including cassava, cereal products etc. can also be attacked. P. truncatus: Stored maize and wheat. Cowpeas, cocoa, coffee, groundnuts, cassava are also subject to attack, as are wooden storage structures and utensils.
Serious primary pests of cereals, parti- culary maize. P. truncatus infests both before and after harvest. P. truncatus is able to develop under drier conditions than R. dominica. Cob maize is more heavily attacked than shelled maize.
Up to 550 eggs (R. dominica) are laid per female on the surface of or among the cereal grains. The larva has legs and eats its way into the grain where it usually pupates. Both larvae and adults are voracious feeders. Under optimal conditions, with a r.h. of 50-60% and a temperature of 34°C, the life cycle takes about 25 days for R. dominica and 27 days for P. truncatus. There have been relatively few studies on the biology of P. truncatus which is a new pest in Kenya, thus far, only established in the Taveta region.
Hodges, R.J. 1982. A review of the biology and control of the greater grain borer Prostephanus truncatus (Horn): (Coleoptera;Bostrichidae). Trop. stored Prod. Inf., 43, 3-9. (A key to the bostrichids commonly associated with stored products is appended. Wright, V.F. 1983. An annotated bibliography on Prostephanus truncatus (Horn), (Coleoptera; Bostrichidae): A pest of stored grain. Trop. stored Prod. Inf. 46, 25-30.
|Species:||Sitotroga cerealella||Angoumois grain moth (Eng.)|
|Majsmal, sädesmal (Swe.)|
Figure 10. Sitotroga cerealella A. adult (from Prevett, 1971) and B. wings (from Weidner, 1982).
Small, straw-coloured moth. Forewing with one or two small black dots. Hindwing with obvious fringe of long hairs, apex sharply pointed. Labial palps curved.
Maize and wheat. Other stored grains and dried fruit can also be attacked.
A primary pest. Only the larva causes damage by hollowing out grain, leaving it with a very small "window". During emergence the adult pushes its way through this small circular window and a "trap door" is left hinged to the grain.
The infestation starts in the field. In store this pest is abundant only on the surface layer of the produce where the larvae bore their way into the grain and feed. Be- fore pupation, they form a channel to the surface of the grain, leaving the seedcoat intact. One female can lay about 100 eggs. The adult are short-lived. The life cycle from egg to adult moth takes about five weeks at 30°c.
|Species:||Ephestia cautella||Tropical warehouse moth or almond moth (Eng.)|
Figure 11. Ephestia cautella A. adult and B. larvae (from Hill, 1983).
The moth is greyish with rather indistinct markings on the wings. Forewing with an outer pale band and an inner broad, dark band with a broad band on its inner edge. When at rest the wings are folded lenghtwise along the abdomen. It averages about 13mm long.
Maize, wheat and other grains in store. Can also attack dried fruit, beans, nuts, banana, groundnut.
A serious intermediate pest. Webbing and frass produced in the infested product are nuisance factors.
The eggs, up to 300 per female, are laid on the produce which the larvae contaminates with webbing and frass as it moves around freely. It feeds, in the case of cereals, largely on the embryo. The pupa is enclosed in a cocoon. The adult moth, which does not feed, lives for less than 14 days. Under optimal conditions, 28°C and 70% r.h., the life cycle is about 4 weeks.
|Species:||Plodia interpunctella||Indian meal moth (Eng.)|
Figure 12. Plodia interpunctella, A. adult and B. larvae (from Hill, 1963)
Outer half of the forewing coppery-red, separated from the creamy inner half by dark grey bands. Body length 6-7 mm, wingspan 14-16 mm.
Mainly meals, flours and farinaceous products. Dried fruit, nuts and some pulses and cereals are also attacked.
Intermediate pest. Damaged caused by consumption of the produce, especially the germinal part of grain followed by contamination of the foodstuff s with silk webbing.
Each female can lay up to 500 eggs which are attached to the substrate. Larvae live and feed in the stored foodstuffs, producing webbing and f rass. Under optimum conditions, 29°C and 75% r.h., the life cycle is about 26 days. Diapause can exist under certain temperature conditions which can render chemical control ineffective.
The traditional way for post-maturity handling of maize: i.e., field-drying, stooking and storage on cobs in structures that do not allow optimal free ventilation, has many disadvantages.
Leaving the maize in the field for 4-8 weeks after maturity exposes it to insects, rodents, birds and rain. The risk of theft is also a concern. Mould will develop on the maize if the cobs are put in granaries while their moisture content is still high; an early rain can also initiate mould problems.
An early harvest followed by quick, proper drying will reduce the above-mentioned disadvantages, and shelling the harvest facilitates insecticide application.
Chemical treatment, on the other hand, may solve some problems but can also cause new ones. Besides the hazards during application and the risk of consuming erroneously treated grain, there are obvious environmental hazards and the insects may also develop insecticide resistance. Farmers have difficulty using correct application rates and spreading the insecticide uniformly. It has also been reported that chemicals other than those approved for admixture in foodstuffs are used such as DDT, aldrin and chlordane (DPRA, 1980). These problems are mostly due to lack of knowledge and information.
Storage at buying centres is only temporary and after purchase, the maize is transported to one of the 40 depots in Kenya where fumigation takes place. Unfortunately, the maize is occasionally left at the buying centres for longer periods and since fumigation is often difficult to conduct at buying centres, significant losses can occur. Present research at NAL emphasizes insecticides; however, there are also ongoing biological studies on the bean weevil, Acanthoscelides obtectus, and ecological studies on Ephestia cautella and Blattisocius tarsalis. The use of edible oils as insect control agents is also being evaluated.
In addition to insecticides, the research at DPRA's On Farm Grain Storage Project also covers storage structure, design, insect-repellent plant materials, inert materals as control agents and the influence of harvest time on post-harvest losses.
The units within the Ministry of Agriculture and Livestock Development and the University of Nairobi emphasise the technical side of storage, i.e. storage structures and the post-maturity handling of maize.
The Pyrethrum Bureau covers the area of pyrethrins as insect control agents.
Cereals and particularly maize, are the main target crops in storage research activities in Kenya. Storage and the control of storage losses of pulses and other crops have not been widely studied thus far.
The high water content (around 80%) in potato tubers makes their storage quite different from that of cereals. For instance, it is important not to lose water if the potato tubers are going to be sold by weight. The high temperatures in the tropics do make storage difficult since they increase respiration, rotting, sprouting and insect damage. During on-farm storage of potatoes in the tropics, losses can occur from the following:
Figure 13. A guide chart to potato store management (from Hunt, 1980)
Durr and Lorentz (1980) estimated losses to be 6-19% over the entire storage period or about 3-10% per month. The ideal storage temperature for ware potatoes is +4°C; however, it is impossible to reach in Kenya without air coolers. But since potatoes are only grown at altitudes above 1800 m, where nights can be quite cool (mean temperatures between 11°C and 12,5°C), they can be stored for up to 3 months at this temperature (Hunt, 1982).
Ventilation decreases respiration, rotting and sprout growth. Cool night air with a high relative humidity can be used as a good compromise between moisture loss due to ventilation and lowered temperature.
The potato market is characterised by large price fluctuations that occur from the time of production to the time of consumption. Although there may be a surplus of potatoes during and just after harvest, scarcity may later result due to the high perishability of the potato combined with inadequate storage facilities.
Storing potatoes in underground pits or delaying harvest are not recommended because of the high risk of rotting and attack by insects and rodents. Neither is sack storage recommended because of high losses due to the lack of ventilation, high temperatures and sprouting.
Clamps: This is the simplest form of acceptable storage, suitable for 1-2 months storage in cooler areas.The pile should be covered with a 15-20 cm layer of straw or grass and 5-10 cm soil. A cover with wire mesh keeps rodents away. One disadvantage is that this form of storage is susceptible to theft.
Heap on the floor: This technique is based on the same principle as the clamp. The heap should not be placed in a corner (bad ventilation). It can be improved by placing an air ventilation duct under the middle of the heap. The risk of theft is minimised.
Slatted box or bin: This form of indoor storage is cheap and effective. The box should be about one metre square and one metre deep and raised about 30 cm above the floor. Planks should all be placed one centimetre apart to facilitate ventilation (Figure 14).
Figure 14. Slatted box or bin (from Hunt. 1982).
Naturally ventilated potato store: This structure is specially made for potatoes. It is expensive but offers a large capacity (about 2100 kg) and satisfactory storage. The structure allows free ventilation, and the walls are isolated with grass or something similar. A naturally ventilated store is shown in Figure 15.
Figure 15. Naturally ventilated ware potato store (from RSL), 1984b).
The International Potato Centre (CIP) is an autonomous, nonprofit, scientific institution, established through an agreement with the government of Peru. Its purpose is to develop and disseminate knowledge leading to greater utilization of the potato as a basic food. International funding sources for technical assistance in agriculture are financing the Centre.
The aim of CIP in the tropical African region is to improve the potato varieties, potato agronomy and the storage of potato tubers.
CIP's potato storage research in Kenya started in 1977 in cooperation with the German Agricultural Team by studying the relationship between night temperature and storage time. Presently, new varieties are being evaluated with respect to their tolerance. Containers for storing ware potatoes are also being evaluated. The aim is to store ware potatoes 3-4 months without the application of chemical sprout suppressants and to store seed potatoes for up to six months. CIP also cooperates with the Rural Structures Unit in their work with the ware potato store and has sponsored parts of the evaluation and construction trials.
Future research will continue on post-harvest technology and associated insects. A dose/mortality bioassay concerning Ac- tellic dust, pyrethrum dust and other admixable insecticides is also planned.
Only a brief description of the organisations and their work is needed since they all cooperate very closely and most of them have already been mentioned in previous chapters.
MOALD-Rural Structures Unit: has carried out trials with various ware potato storage structures. The structure shown in Figure 15 is soon to be used in RSU's extension programme. The manuals have already been compiled but not published.
University of Nairobi, Department of Agricultural Engineering: has tested ware potatoes storage structures in their storage trials. For the moment, there are no such trials in progress.
National Agricultural Laboratories: has ongoing research on residue levels after treating potatoes with insecticides to control the potato tuber moth (Phthorimaea operculella). The following insecticides will be investigated: permethrin, etrimfos, malathion, pirimiphos-methyl, quinalphos, cypermethrin, fenvalerate.
MOALD-Crop Production Division: is responsible for the trials and the Crop Storage Engineer at the division coordinates the work within the ministry and other organisations.
Among the insects attacking stored potatoes is the potato tuber moth, PTM (Phthorimaea operculella) by far the most important (Raman and Booth, 1983). A serious pest in stored seed potatoes is the green peach aphid (Myzus persicae) since it attacks the sprouts and vectors potato leafroll virus (Parker et al. 1983).
The potato tuber moth
The potato tuber moth (P. operculella) can cause extensive damage to both growing and stored potatoes. During growth the larvae live as miners in the foliage and stems. The infestation can continue in storage since larvae attack tubers prior to harvest and adults lay eggs on exposed tubers. Infestation caused by adults entering the store can also occur.
Infestation rates in stored potato tubers by PTM have been reported to reach 90% following 2 months storage (CIP, 1981).
Besides the direct losses caused by larvae, infested tubers are very susceptible to rotting after larval penetration. The sprouts can also be damaged, which is a serious problem in seed potatoes.
Environmental hazards and pestcide resistance problems (Haines, 1977) could be decreased using an integrated pest control approach to the problem.
The following techniques can be used (Raman and Booth, 1983):
Figures 16 to 19 are the results from trials conducted in Peru and show numbers of sprouts damaged and numbers of tubers rotting due to larval penetration followed by decay after 120 days of storage.
1. Repellent plant material: A weed, Lantana sp., that occurs commonly in the tropics has proved very effective in repelling PTM (see Figure 16). The dried and chopped leaves can either be spread on top of the tubers or mixed with them.
Figure 16. Comparison of some traditional practices for control of p. operculella (from Raman and Booth, 1984).
2. Biological insecticides: "Dipel", commercially marketed active spores of Bacillus thuringiensis, has been shown to reduce both sprout damage and rotting (Figure 17). The material was supplied as a single spray prior to storage.
Figure 17. Effect of Bacillus thuringiensis (Dipel) in controlling P. operculella (from Raman and Booth, 1984).
3. Sex pheromones: The sex pheromones of PTM can be obtained commercially at a cost of about 24 KSh per capsule (Hunt, 1984). One trap per 10 m2 storage area is placed inside the store. The attracted males either drown in the trap or get stuck on a sticky paper depending on the trap design. The damage caused by PTM was reduced by more than 80% (Figure 18). Pheromone traps also have potential as a monitoring tools in larger stores where fumigation can take place.
4. Water cooling: Water trickling down the screen walls of the store causes evaporative cooling. This reduces PTM damage since the moth is sensitive to low temperatures. PTM does not remain seriously active below an average temperature of 16°C (Figure 18).
Figure 18. Use of synthetic sex pheromone and water (humidification) for control of P. operculella (from Raman and Booth, 1984).
5. Admixing residual insecticides: The possibility of PTM (like all other insects) developing resistance to insecticides makes it advisable to limit their use. The insecticide used in the trial was Fenvalerate, a synthetic pyrethroid. Spraying with 0.2% Fenvalerate, eight times during the 120- day storage period (every 15 days) controlled PTM to the same extent as did the single spray with active spores of B. thuringiensis.
Figure 19. Effect of synthetic pyrethroid (Fenvalerate) applications at different spray intervals on P. operculella (from Raman and Booth. 1984).
Potato tuber resistance to PTM attack is also under evaluation in Kenya. Immunity to PTM damage has not been reported but different levels of tuber damage have been found which were associated with certain potato races.
The green peach ahpid, GPA (Myzus persicae)
Although not important in ware potato stores, it can cause serious damage in seed potato stores since it vectors potato virus Y. The most effective way to reduce viral transmission by GPA is to spray with a systemic insecticide when tubers start to sprout.
Lantana sp. repels GPA but this plant's effectiveness has not yet been evaluated.
Potato storage for cooperatives and other organisations is not a major problem where they can afford a cooling system that makes storage easier. It is generally the smallholder farmer that has to face the problems of severe sprouting and moisture loss. If they want to keep ware potatoes after the dormant period (on average, 2 months) they usually are forced to use chemical sprout suppressants to prevent heavy sprouting or, they are forced to sell the potatoes shortly after harvest for a low price, since the market is flooded by that time. Thus, potato storage research is aimed at developing methods that would allow smallholder farmers the possibility of storing potatoes for 3-4 months, hopefully without the use of chemical sprout suppressants. It is also advantageous for consumers to have a steady, even supply of high quality potatoes.
The present potato storage research concerns the storage ability of the potato tubers and different kinds of storage structures have, for that reason, been evaluated. NAL is currently studying the residue levels arising from treatment of potatoes with insecticides to control the potato tuber moth, PTM, (Phthorimaea operculella). Other than the research reported on here, little has been done to evaluate methods for controlling PTM in stored ware potatoes. Presently, potato tuber moth control in stores is not widely practised. Integrated pest control has been tested in Peru (Raman and Palacios, 1982; Raman and Booth, 1983) and probably holds promise in Kenya, as well.
During the course of my field studies, about 25 smallholder farmers were visited. Most of them have had an improved maize crib constructed on their farm by the Rural Structures Unit. Some of these farmers had both an improved crib and a traditional one.
All farmers interviewed had very positive attitudes toward early harvesting and crib drying, but not all were keen on the idea of shelling all of their maize at once after the drying period. In areas with a short supply of maize, many preferred to keep their maize in dwellings instead of cribs to protect against theft.
The methods of protecting grain during storage have thus far been limited to pesticide applications except for the limited use of ashes and smoking. Pesticides have the benefits of being very cheap, fast acting, relatively easy to apply and effective as long as resistance has not developed. However, there are also a multitude of problems connected with the use of pesticides, and their use should be limited to curative actions in "emergency" situations. Presently, chemical control trials take a major part of the research resources.
Although there are other alternative control methods, the inexpensiveness and efficiency of insecticides has encouraged departure from the use of and research on these other methods. This has often led to reliance on insecticide applications, since it is usually the only method available. Other possible methods of stored product pest control for the smallholder farmer are discussed below.
Alternative control strategies of potential use in the future include the introduction of natural enemies or sterilised male insects, treatment with insect growth regulators and modification of the physical environment through temperature regulation, microwave transmission, atmoshpere modification etc. However, these and other methods have yet to be proven efficacious and are prohibitively expensive for use by Kenyan smallholder farmers.
There are some practical, cultural methods, however, that can reduce insect attack and the use of insecticides. Early harvesting, which can reduce the initial field infestation, has already been mentioned but is not widely practised. Sanitation is another simple but effective prevention method which does not receive the appreciation that it should from farmers.
Groundnut oil has been proven effective against Sitophilus zeamais (Ivbijaro, 1984). 20 ml per kg maize caused 100% mortality of adult weevils within 24 h. Kenya is not a producer of groundnut oil but produces large quantities of maize oil and sunflower oil. These oils might be as effective as groundnut oil,
To find locally available materials that work as effective control agents would be very beneficial. Trials in Poland have shown tricalciumphosphate to be effective against Tribolium castaneum and Rhizopertha dominica (Boczek, 1980). DPRA has conducted some research on the potential use of repellent materials and inert materials such as diatomite and blue pumice. NAL has a proposal for similar research. These materials have good potential as control methods for smallholder farmers.
Pheromones offer other control and monitoring methods that could be useful in Kenya. In Great Britain, a pheromone has already been used for monitoring Ephestia kühniella (Anon. 1980). Pheromones have also been identified for Plodia interpunctella, Ephestia cautella (Kuwahara et a1., 1971) Sitotroga cerealella (Vick et. a1., 1974) and Tribolium castaneum (Suzuki and Muri, 1983). It has been proved that Rhizopertha dominica (Khorromshahi and Burkholder, 1981) and Sitophilus spp. (Burkholder and Phillips, 1982; Faustini et al., 1982) communicate with the help of pheromones but they have not yet been identified. Until they are mass-produced and marketed at low cost, pheromones probably will be limited to control/monitoring in commercial storage areas. The same thing can be said about other semiochemicals.
An insect pathogen. Bacillus thuringiensis, is already available commercially in the US for admixing in stored grain for protection against lepidopterous larvae. It would certainly be advantageous for Kenya to try out this method.
In countries such as Malawi (Schulten, 1969) and Belize (Fortier et al, 1982) it has been reported that hybrid maize does not have the same storage capability as the local varieties. Higher yields of hybrid maize may compensate for the higher losses in Kenya. Plant breeders should work more closely with entomologists to produce varieties that have desirable agronomic characteristics combined with resistance to storage pests.
Integrated pest management (IPM) is a management strategy, incorporating all possible preventive and suppressive strategies which are only used after a thorough decision-making process based on both biological and economic evaluations. Thus far, no well-developed IPM program is available for storage pests.
Integrated pest management is not yet widely practiced. To use an integrated pest management appraoch to the storage insect pest problem as many control methods as possible should be used side by side so as to to achieve optimal protection. Pesticides are only one part of IPM and relying on a single method will not solve any problems in the long run since resistance will likely develop.
In the case of the potato tuber moth (P. operculella), an integrated system of control methods has been found effective in Peru and may work as well in Kenya. This might be a part of a complete IPM program in the future.
An interesting alternative for buying centres might be the ferrocement store if its size was increased from the present capacity of 250 bags to about 2500 bags. Fumigation in the ferrocement store has not been tested but if it works, then maize could be left at the buying centre until transported to a deficit area without passing a depot. This would save time and transport costs. It is also a good strategy to have stored food decentralised. If the store is sufficiently air- tight, then it might even be possible to use carbon dioxide as a fumigant - a less hazardous compound that could be applied by the staff at the buying centre.
GAT/GTZ is looking for a suitable village storehouse that could be fumigated. The ferrocement storehouse could be a good structure for that purpose at relatively low cost.
A simple structure for storing occasional surplus grain at buying centres and depots could be a concrete platform, raised above the ground and provided with rat guards. After stacking the bags, the piles could then be covered with tarpaulins and fumigated. The tarpaulins could be left covering the pile until the bags are removed. A trial carried out in Australia (Annis, 1981) showed that it was possible to use carbon dioxide for fumigating bag stacks of rice sealed in flexible PVC-enclosures. 2.2 - 2.9 kg CO2 per ton rice was used and gave good protection against reinfestation for up to 133 days after treatment.
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